nehruelearning.innehruelearning.in/images/745/dot_net1.docx · Web viewTable of Contents. Unit I. Part. I-Introduction. Chapter1-Introductionto.NET. Chapter2-VB6andVB.NETDifferences

Table of ContentsUnit I

Part I-IntroductionChapter 1 -Introductionto.NETChapter 2 -VB6andVB.NETDifferencesPart I I -The VB.NET Programming LanguageChapter 3 -Object-OrientedProgramming and VB.NETChapter 4 -HelloWorldChapter 5 -DataTypes, Variables and OperatorsChapter 6 -ArraysChapter 7 -ConditionalLogic

Unit IIChapter 8 -ProceduresChapter 9 -DialogBoxesChapter1 0 -FileIOandSystemObjectsChapter1 2 -ErrorHandlingChapter1 3 –NamespacesChapter 1 4 -ClassesandObjectsChapter1 5 -MultithreadingChapter1 6 -COMInteropandMSMQ

Unit IIIPart II I -VisualStudio.NET:TheIDEforVB.NETChapter1 7 -VisualBasic.NETIDEChapter1 8 -Compiling and DebuggingChapter1 9 -CustomizingPart I V -Data AccessChapter2 1 -Introduction to Data Accessin.NET Chapter2 2 -ADO.NETPart V -Windows FormsChapter2 5 -Introduction to System.Windows.FormsChapter2 6 -ControlsChapter2 7 -SpecificControlsChapter2 9 -IrregularForms

Unit IVPart V I - VB.NET and the WebChapter3 1 -Introduction to WebDevelopmentChapter3 2 -Introduction to ASP.NETChapter3 3 -Page FrameworkChapter3 4 -HTML Server ControlsChapter3 5 -WebControlsChapter3 6 -Validation ControlsChapter3 8 -EventsChapter3 9 -Cascading Style SheetsChapter4 0 -State ManagementChapter4 2 -TracingChapter4 3 -Security

Unit VPartVI I -WebServicesChapter4 4 -Introduction to WebServicesChapter4 5 -WebServices InfrastructureChapter4 6 -SOAPChapter4 7 -Building a WebServiceChapter4 8 -Deploying and Publishing WebServicesChapter4 9 -Finding WebServicesChapter5 0 -Consuming Web Services

PartI:Introduction

Chapter 1 :Introduction to .NETChapter 2 :VB6 and VB.NET Differences

Chapter1:Introduction to .NETWhat is.NETThe.NET FrameworkCommon Language RuntimeBase Class LibrariesVB.NET

.NET Defined

.NETisMicrosoft'splatformforbuildingXMLWebServices.

Moreimportant,however,iswhat.NETdoesforyou.Nomatterwhatyourdefinitionof.NETmightbe,orwhatyoureadaboutinmagazinesandontheWeb,theendgoalisto provideaplatformfordevelopinganddeployingWeb-basedservices,orWebServices, inasimple,secure,andconsistentmanner.Thisdoesnotmean,however,thatyouwill onlybewritingwebservicesforallofyournew.NETcoding.Therearegreat technologicalachievementsin.NETthatgofarbeyondtheabilitytocreateandconsumewebservices,andthroughoutthischapterandthroughoutthisbookthiswillbecomeveryclear.

EnterSOAP.TheSimpleObjectAccessProtocol,orSOAP,wasthefirsteffortin enablingacommonandconsistentmechanismformovingdataoverHTTPtoanytype ofcomputer.SOAPisasetofXMLspecificationsthatdescribeshowdatacanbesent andreceivedovertheInternet.ASOAPmessagecontainsinformationaboutitself. Thereare"parts"toaSOAPmessagethatdefinethemessagecontent,theintentofthe message,andhowtosenddatabacktothesenderoftheSOAPrequest.

InordertohaveaconsistentandcommonplatformforbuildingWebServices,there neededtobeaconsistentandcommonwayofcommunicatingovertheInternet.With SOAP,XMLcanbeusedtohandleanyrequest,andbecauseXMLisjustaself- describingtextfile,anytypeofoperatingsystemorbrowsercanconsumeSOAP-based WebServices.

ThesoftwareasaserviceparadigmcanbeaccomplishedbyusingSOAPasthe commonprotocol.AnyWebsitecanofferaservice,andtheserveronthebackendcan accepttherequestforthatservicethroughthestandardport80thatHTTPuses.Itcan thensendtheresultsbackdowntotheclientasXML,andtheclientcanmanipulatethe dataisitseesfit.

The.NETexperience

Figure1-1: The.NETexperience

WithVisualStudio.NET,youhavethetoolsyouneedtoleverageyourexisting knowledgetocreateapplicationsfor.NET.VisualBasichasalwaysbeenknownfor providingthedeveloperwiththemostefficientIDEfordevelopingWindows-based applications.WiththeintroductionofVisualInterDev,Microsofttriedtocreatethesame ease-of-useGUIforcreatingWeb-basedapplications.IfyouhaveeverusedInterDev, youknowthatitfellshortinbeingtheRapidApplicationDevelopment(RAD)toolforthe Internetitwaspromisedtobe.VisualStudio.NETistrulyRADfortheInternet.Withthe bestofallworlds,fromVisualBasictoInterDevtoFrontPagetoanyotherGUItoolyou haveeverused,VisualStudio.NETisacombinationofeverythinggreatMicrosofthas everproducedinadevelopmentenvironment.

Ifyouarelikeme,youdonothavetimetolearnbrandnewstuff.Youhaveenoughtodo atworkasitis,letalonelearnaboutSOAPandhowtomakeitworkwith.NET.With VisualStudio.NET,XMLis"baked"in;itiseverywhere,andyoudonothavetoknow whereorhow.Everythingtothedeveloperistransparent;allyouneedtoworryaboutis coding.TheplumbingthatgoesintomarshallingXMLfromclienttoserverisnotanissue.ImentionedRADfortheInternet,butVS.NETisalsoRADfortheserver.Itisaunifiedenvironmentfordevelopingclient-andserver-basedapplicationsandservices,in justaboutanylanguageyouchoosetouse,fasterandeasierthanever.Andbestofall,itisbasedonstandardsthatareinplacetoday,suchasXML,SOAP,HTTP,andHTML.

The .NET FrameworkThe.NETFrameworkistheplumbingof.NET.Theframeworkprovidestheservices necessarytodevelopanddeployapplicationsforthelooselycoupled,disconnected Internetenvironment.Figure 1 - 2showsthekeycomponentsoftheframework.

Figure1-2: The.NETFramework

ThetwomaincomponentsthatmakeuptheframeworkaretheCommonLanguage Runtime(CLR)andtheBaseClassLibraries(BCL).Everythinginthisbookrelatestothe BCL.Asadeveloper,youarecodingagainstclasslibraries,whichareallderivedfrom theBCL.Inthefuture,youmaybeusingthird-partyclasslibrariesthatarenotpartofthe baseclasses,buttheymuststillbebasedontheCLRspecifications.

Othercoreservicesincludecross-languageinteroperability,security,managed execution,andtheCommonTypeSystem(CTS).Together,theseservicesmakeupthe.NETFramework.

Common Language Runtime

TheCLRisthefoundationoftheframework.ThegoalsoftheCLRareasfollows: Secure and robust execution environment Simplified development process Multilanguage support Simplified management and simplified deployment

AsImentionedearlier,IalwaysthoughtWindowsDNAwastheend-alltoprogramming concepts.InmyworldofWindowsonly,Ineverranintoanyinteroperabilityissues,butin reality,thatwasamajordrawbackoftheCOMtechnology.COMprovidedagreatwayforapplicationstointegrate,buteachapplicationhadtosupplytheunderlyinginfrastructure,andtheobjectshadnodirectinteraction.Thisdoesnotmakeforavery globalconcept.Inorderforanyapplicationtoconsumeanytypeofservice,thereneeded tobeabetterwaytohandlecross-processandcross-platformcommunication.

SecureandrobustexecutionenvironmentTheCLRprovidestheenvironmentthatmanagescodewhenitisexecuted.Codethat runsinsidetheframeworkisknownasmanagedcode,whichrunsundercertainrules providedbytheCLR.ManagedcodesuppliestheMetadata(dataaboutdata)necessary fortheCLRtoprovideservicessuchasmemorymanagement,cross-language integration,codeaccesssecurity,andautomaticlifetimecontrolofobjects.Codebased onMicrosoftIntermediateLanguage(MSIL)executesasmanagedcode.Managedcode isthecoreconceptoftheframework.Withmanagedcode,CPU-specificcompilerscan bebuilttohandletheintermediatelanguage'srequest.Inthistypeofscenario,theCOM modelisoutdated.

TheMSIListheoutputproducedwhen.NETapplicationsarecompiled.Thisisasemi- newconceptforVBdevelopers.Inthepast,youcouldeithercompileto"native"code (whichwasn'treallynativeatall),oryoucouldcompiletoP-Code,whichwasinterpreted bytheVBruntimewhenyourapplicationexecuted.TheMSIListhelanguagethatallof the.NETlanguagescompiledownto.Aftertheyareinthisintermediatelanguage,a processcalledJust-In-Time(JIT)compilationoccurswhenresourcesareusedfromyour applicationatruntime.JITallows"parts"ofyourapplicationtoexecutewhentheyare needed,whichmeansthatifsomethingisneverneeded,itwillnevercompiledowntothePE(portableexecutable)filethatisthenativecode.ByusingJIT,theCLRcancache thecodethatisusedmorethanonceandreuseitforsubsequentcalls,withoutgoing throughthecompilationprocessagain.Figure 1 - 3 describestheJITprocess.

Figure1-3: JITcompilationprocess

TheJITprocessenablesasecureenvironmentbymakingcertainassumptions: Typereferencesarecompatiblewiththetypebeingreferenced. Operationsareinvokedonanobjectonlyiftheyarewithinthe

executionparametersforthatobject. Identitieswithintheapplicationareaccurate.

Byfollowingtheserules,themanagedexecutioncanguaranteethatcodebeing executedistypesafe;theexecutionwillonlytakeplaceinmemorythatitisallowedto access.ThisispossiblebytheverificationprocessthatoccurswhentheMSILis convertedintoCPU-specificcode.Duringthisverification,thecodeisexaminedto ensureitisnotcorrupt,itistypesafe,andthecodedoesnotinterferewithexisting securitypoliciesthatareinplaceonthesystem.

Exceptionhandling

TheframeworksupportsStructuredExceptionHandling(SEH)acrosslanguagesand processes.Whenyoucompileyouapplications,tablesarecreatedbasedonthe methodsintheclassesandtheerrorsthatcanoccuraremappedtohandlersinyour methodcalls.Inanunmanagedenvironment,errorswerepassedthroughHRESULTs andBooleanreturnvalues,andtherewasnocommonwaytohandleanerrorifitdid occur.In.NET,errorhandingisintegratedwiththeframework;itisnotanafterthought.

Garbagecollection

Objectlifetimeismanagedthroughaprocesscalledgarbagecollection(GC).Through GC,releasedobjectreferencesareautomaticallyreclaimedbytheoperatingsystem.In VB6,youhadtoexplicitlysetobjectsequaltonothingtoensurethatmemorywas regained,andinC++,overlookingthereleaseofobjectscausednastymemoryleaks.In.NET,memorymanagementisautomatic,andmemoryisreclaimedwhentheruntimedecidesthattheobjectreferencesarenolongerinuse.

SimplifieddevelopmentSimplifieddevelopmentcouldmeanalotofdifferentthingstoalotofdifferentpeople.In somecases,itcouldmeanthecomputerreadingyourmind,savingyoualotoftyping.In othercases,itcouldmeanwinningthelotteryandretiringtoabeachsomewhereinthe SouthPacific,ormaybeevena20-million-dollar(586,440,010.07Russianrubles)rideto Alpha,thatcoolspacestationcirclingtheearth.In.NET,simplifieddevelopmentmeans morethananyofthat.

Oneofthebiggestchangesintheframeworkistheeliminationoftheregistry.Theregistryistheenemyofalldevelopers.GUIDs,IDLfiles,HRESULTs,andallotherCOM- relatednightmaresgoawayin.NET.

ThegoodnewsisthatyoucanstilluseyourCOMcomponentsin.NET.

JustlikeaddingareferencetoaDLLinVB6,youcanaddareferencetoaCOMDLLin.NET,anditwillcreateawrapperfortheDLLthat.NETcanusetoaccessthemembers intheDLLinamanagedenvironment.Youcanalsocall.NETassembliesfroman unmanagedenvironment,suchasVB6.Bothofthesefeaturesrequirenoadditionalwork onyourpart,soyouhaveaveryflexibleenvironmenttouseyourexistingcodeina.NET application,ortouse.NETassembliesinaVB6environment.

Object-orientedfeatures

AnewconcepttoVBdevelopersisobject-orientedOOprogramming.OOsimplifiesthe reuseandinteroperabilitybetweencomponents.Theclassesintheframeworkareall100%object-oriented.ThenicethingabouttheBCLbeing100%OOisthatyoucan implementOOfeaturesacrosslanguages,suchasinheritanceandpolymorphism.This isakeyfactortosimplifieddevelopmentinlargeshopswheresomeprogrammersmight beusingVB.NET,whereasotherdeveloperscouldbeusingCOBOL.NETorC#.No matterwhatyourlanguagechoice,thesamefeaturesareavailabletoeveryone.

VisualStudio.NETTheVisualStudio.NETIDEisthebestpartofsimplifieddevelopment.Thetools availableinVS.NETallowyoutoquicklyandeasilydeveloplarge-scale,distributed applications.Chapter1 7 delvesintothefeaturesoftheVS.NETIDE,andIamsureyou willbeveryimpressedasyoustarttouseitintherealworldtodevelopapplications.

MultilanguagesupportAsoftoday,thereareroughly18languagesthattheframeworksupports.FromPascalto COBOLtoJScript,youhavecompletefreedomoverthetoolyouusetodevelopyour applications.AstheCLRgainsmoreacceptance,therearesuretobeadditional languagesaddedbyothercompaniesbesidesMicrosoft.

OutoftheVS.NETbox,MicrosoftshipswithcompilersforJScript.NET,VisualBasic.NET,C#,andManagedC++..AlloftheselanguagesarefullysupportedintheVS.NET IDE,andtherearecommand-linecompilersforeachoftheselanguages.Theother15or solanguagesarecomingfromthirdparties,andtheywilleitherhavetheirownIDEor theywillhookintotheVS.NETIDE.

Howisthispossible?The.NETFrameworkdefinesasubsetofrulesthatdefineshowa languagecanbeconsumedbytheCLR.ThesetofrulesiscalledtheCommon LanguageSpecification(CLS).TheCLSallowsanythirdpartytocreatealanguagethat cantargetthe.NETFramework,aslongasthespecificationslaidoutintheCLSare followed.

BecauseoftheCLS,languageinteroperabilityispossible.ComponentswritteninVB.NETcanbeconsumedfromC#orManagedC++,noextracoderequired.Passing stringsfromManagedC++toVB.NETdoesnotrequirestrangeconversionfunctionsthatwillallowVB.NETtousethedata.In.NET,astringisastring,thesameinall languages.ThisispossiblebytheCommonTypeSystememployedbytheframework, definedintheCLS.TheCTSdefineswhattypesareallowedtoruninsidetheframework.Atypecanbedefinedasavaluetypeorareferencetype.Valuetypesarestoredasarepresentation oftheirvalue,suchasdatatypes.Referencetypesarestoredasareferencetoatype, suchasanobject.Referencetypesin.NETarebasedontheSystem.Objecttype, andtheycanbefurtherbrokendownintoclassesthatderivefromtheSystem.Object type.Figure 1 - 4describestheCTSasimplementedinthe.NETFramework.

Figure1-4: CommonTypeSystem

Debugging,tracing,andprofilingareavailableacrosslanguagesandacrossmachines. Sincetheseprocessesarebasedonwhatoccursatruntime,asingledebuggercanbe usedacrossalllanguagesbecauseitisinteractingwiththeMSIL,notthespecificsofa particularlanguage.

Alllanguages,nomatterwhatdeveloper-specificfeaturesthelanguageoffers,stillhave tocompiledowntotheMSIL,andthengetinterpretedbytheCPU-specificexecution engine.Thismeansthatalllanguagesareonalevelplayingfield.Alllanguagessupport thefeaturesofthe.NETFramework,orelsetheywouldnotbeconsidereda.NET language.

Therearelanguage-specificfeaturesbasedonyourlanguagechoice,whichcouldincludebuilt-infunctions,keywords,orlanguagesemantics,butwhenthefileisbuilt,itis builttotheMSIL.Thelanguage-specificcompilerwillensurethatthecodeistypesafe andwillpasstheMSILverificationprocess.Thisisnottosaythatcertainrulescannotbe broken,soyoushouldinvestigatetheCLSandCTStomakesureyouareusingCLS- complianttypes.VB.NETisanexampleofalanguagethathasspecialfeaturesthatotherlanguagesdonot.Becausethereareroughly12millionVBdeveloperswhohave10,000timesthatin linesofcodewritten,Microsofthasincludedanupgradepathforexistingapplications. Thisupgradepathusesacompatibilitylibrarythatcontainsmanyofthesamekeywords andfunctionsyouareusedtousinginVB6.WhenyouarecodinginVB.NET,functions suchasMsgBoxarestillvalid,eventhoughtheBCLhasaMessageBoxclassthatis morerobustandshouldbeused.Essentially,theMsgboxfunctionhasacompatibility wrapperthatactuallycallsthenativeBCLMessageBoxclassmembers.

SimplifieddeploymentandmanagementThemainunitofdeploymentin.NETisanassembly.Althoughassembliescanhavea.dllextension(theycanalsohavethe.exeextension),theyarenottraditionalCOM DLLs.Assembliescontainamanifest,whichisMetadatathatis"emitted"tothecallersof theassembly.TheMetadatacontainsthenameoftheassembly,theversion,theculture,andoptionally thepublickeyfortheassembly.Otherinformationintheassemblyincludeswhattypes areexported,whattypesarereferenced,andthesecuritypermissionsforeachtype. Assembliescomeintwoflavors:privateorshared.

Privateassembliesaredeployedthrougha"zeroimpactinstall"process.Zeroimpact installmeansthatyounolongerhavetocrossyourfingerswhenyoudeployan application,becausetheapplicationinstallationisnotaffectingthestateofthemachine. Becausetheregistryisnotinvolved,yousimplycopythefilesthatyourapplicationneeds toexecutetothedirectoryinwhichitwillrun.ThisprocessiscalledXCopydeployment. That'sright,XCopyfromthe oldDOSdays.Youarejustcopyingfiles,anditalljust works.SharedassembliesarecopiedtotheGlobalAssemblyCache(GAC).TheGACis arepositoryforfilesthatcanbesharedacrossmultipleprocesses.Whenassembliesare installedtotheGAC,theyareboundbyversionandpoliciesdefinedbythepublisherof theassembly.

.NET.Onthesamemachine,inthesameexactprocess,DLLswiththesamenamebut differentversionscanbeexecutingatthesametime.

BaseClassLibraries

The.NETFrameworkprovidesasetofhierarchicalobjects,brokendownby functionality,calledtheBaseClassLibraries(BCL).Theclassesprovideasetof common,object-orientedinterfacesthatcanbeaccessedfromany.NETlanguage.

TheBCLisdividedintonamespaces,whichdefineanamingschemeforclasses,such aswebclasses,Dataclasses,WindowsForms,XMLclasses,Enterpriseservices,and Systemclasses.Byimplementinganamingscheme,itiseasytocategorizewhat functionalitytheclassesareactuallygoingtoprovide.Forexample,theDataclasses providethefollowingtop-levelnamespaces:

System.Data System.Data.Common System.Data.OLEDB System.Data.SQLClient System.Data.SQLTypes

Eachoneofthedatanamespacesisbrokendownfurtherintomoregranularclasses, whichdefinethemethods,fields,structures,enumerations,andinterfacesthatare providedbyeachtype.

TheSystemclassprovidesthebaseservicesthatalllanguageswouldinclude,suchasIO,arrays,collections,security,andglobalization.Becausetheclasssystemisunifiedforalllanguages,itisnotimportantwhatlanguageis attemptingtoaccessthebaseclasses,allofthefeaturesareavailabletoalllanguages, andthewayinwhichthecodeisimplementedisthesame.Thisactuallymakesitvery easytounderstandcodewritteninotherlanguages.Becausetheclasslibrariesinusearethesame,theonlydifferenceinthecodeisthesemanticsofeachspecificlanguage.

Visual Basic .NETLanguage innovations

VB.NETisfinallyafirst-classlanguage.Everyfeaturethatisprovidedbytheframework isavailableinVB.NET.VB.NETisafullyobject-orientedlanguage,providinginheritance,polymorphism,encapsulation,overloading,andoverriding.Withstructured exceptionhandling,thereisacleanandconsistentmethodofhandlingerrorsnotonly withinamethod,butalsoinacallingchainofmultiplemethods,andevenacross componentswritteninotherlanguages.

RADfeatures

TheVS.NETtoolprovidesthemostRADtooleverdevelopedtoassistyouinevery possiblewaywhilewritingcode.Withimproveddesigners,serverexplorers,data designers,andXMLdesigners,youhavealltheexternaltoolsatyourfingertipstowrite client-andserver-basedapplications.Allofthiswithouthavingtolearnanythingnew, becausetheVS.NETIDEwillbefamiliartoyouifyouhaveusedanyofthepreviousVB versions,orevenVisualInterDev.IDEfeaturessuchasautocompleteandauto-list membershavebeenimprovedtomakeiseasierthanevertoverifyyourcodeasyouare developing.

WebForms

WebFormsallowthedevelopmentofscalableWeb-basedapplicationsinafamiliarVB- likeIDE.FeaturessuchascodebehindminimizethespaghetticodeproducedbyVisual InterDev,andwithdown-levelbrowsersupport,nospecialcodeisneededtotarget specificbrowsertypesorversions.TheIDEisthesameforWindows-basedapplications, soallofthefeaturesavailabletodevelopingWindows-basedapplicationsareavailable whenbuildingWeb-basedapplications.

WebServicesByprefixingamethodwiththe<webmethod>identifier,whichisanexampleofattribute- basedprogramming,youhavejustcreatedaWebServicecallablemethod.The underlyingplumbingishandledbytheIDE,anddeploymentisaseasyascopyingafiletotheWebserver.CreatingaWebServiceisaseasyascreatinganyothertypeofapplication.

WindowsForms

WindowsFormsarearewrittenformsenginetargetedspecificallyforthe.NETplatform. ThesameclassesthatareusedinVB.NETaresharedacrossalllanguages,and WindowsFormscanevenrunasasemi-trustedorfullytrustedbrowsercomponent.

Chapter2:VB6andVB.NETDifferencesIn This Chapter

DatatypechangesArraychangesOperatorchangesVariablescopingandinitializationProceduresandpropertieschangesControlofflowFormschangesApplicationtypechanges

Data Type ChangesThe.NETFrameworkhasclassesthatdefinetheCommonTypeSystemthatallowfor datatypestobeconsistentacrossapplicationswrittenindifferent.NETlanguages. Becauseofthis,VisualBasicneededtochangethetypesofdataitsupportsandthe numericrangesofexistingdatatypes.Thefollowingsectioncoversthedifferences.

VariantnotsupportedInVB6,theVariantdatatypewasthedefaultuniversaldatatype;thiswasreplacedby theObjectdatatypeinVB.NET.ThedefaultvalueforObjectdatatypesisNothing, whereasthedefaultvalueforVariantdatatypeswasEmpty.

Dimvar1asVariant

Changesto:

Dimvar1asObject

IntegerandLongInVB6,theIntegerdatatypewasa16-bitnumber,ranginginvaluefrom–32,767to32,767.TheShortdatatypereplacesIntegerasa32-bitnumberinVB.NET,andthe Integerdatatypenowrangesfrom–2,147,483,648to2,147,483,647.TheLongdata typeisnowa64-bitnumber.UsingIntegerfor32-bitoperationsisthemostefficient datatype.

DimXasInteger

DimYasLong

Changesto:DimXasShort

DimYasInteger

CurrencynotsupportedTheCurrencydatatypeischangedtodecimalinVB.NET.Decimalismoreaccurate forroundingnumbers,sotheDecimaldatatypewascreatedtohandlecurrency operations.Currencywasa64-bitnumber,with4digitstotherightofthedecimal place.ThenewDecimaldatatypeisa96-bitsignedintegerandcanhaveupto28 digitstotherightofthedecimalplace.

DimXasCurrency

Changesto:

DimXasDecimal

DatechangesTheDatedatatypeisnowa64-bitinteger,whereasinVB6itwas64-bitdouble.To accommodatethecodeusedintheDatedatatype,youhavetheToOADateand

FromOADatefunctionstoconvertbetweenDoubleandDatedatatypes.

DimXasDouble

Changesto:

DimXasDouble,YasDate

Y=X.ToOADate

Strings

Fixed-lengthstringsarenolongersupported.SDKdocumentationstatesthatthis functionalitywillbeaddedinfutureversions.Thereisacompatibilitylayerthatallowsfor fixed-lengthstrings,buttheyarenotdirectlysupportedbytheCLR.

DefTypenotsupportedTheDefTypestatement,whichgivesadefaulttypeforallvariablesdeclaredwithouta type,isnolongersupported.DefInt,DefStr,DefBool,andDefLngarenolonger supported.

VarPtr,StrPtr,ObjPtrThesefunctions,whichreturntheintegeraddressesof variablesin APIcalls,areno longersupported.TheAddrOfPinnedHandlemethodoftheGCHandleclasscan providesimilarfunctionality.

ArraysOneofthebiggestissueswhenMicrosoftannouncedthelanguagechangesinVB.NET wasthelower-dimensionarrays.Fromthebeginning,VisualBasichasalwaysallowed thelowerboundofanarraytobeeither0or1.TheOptionBasestatement,whichis nolongersupported,dictatedwhetherallarraysshouldbetreatedas0-basedor1- based.Intheend,Microsoftdecidedthatallarrayswillhaveadefaultlowerboundof0, meaningthatexistingcodeusingtheOptionBase1statementwillneedtobe revisitedtoensurethatthereisnodatalossorcorruption,becausethesizeofthearray willbedifferent.

Arrayscannotbefixed

Arrayscannotbedeclaredasfixedsizesbyspecifyingthelowerandupperboundsat designtime.Younowdeclarejusttheupperboundtothearray,withzerobeingthe defaultlowerbound.

Dimx(0to5)asstring'6itemarray

Changesto:

Dimx(5)asstring'6itemarray

Or

DimXasString=newString(5)'6itemarray

OptionBasenotsupportedTheOptionBasestatementtospecifythelowerboundsforallarraysinamoduleor formisnolongersupported.Thedefaultlowerboundforallarraysiszero.

ReDimchangedTheReDimstatementcannotbeusedinthedeclarationofanarrayvariable.InVB.NET, youdeclareanarrayusingDim,andthenusetheReDimstatementtoaltertheboundsofthearray.

The Value of TrueInVB6,thevalueoftrueis–1.ThisisthesameinVB.NET,however,intheCommon LanguageRuntime;thevalueoftrueisequalto1.WhenpassingBooleanvariables betweenlanguagesinthe.NETFramework,–1willbetrueinVB,and1inallother languages.

OperatorsSomeofthemostexcitinglanguagechangesinVB.NEThavecomeinthecategoryof operators.Table2 - 1liststhenewassignmentoperators,whichwillmeanlesstypingfor youwhenyouareusingoperators.

Table2-1:NewAssignmentOperators

Operator Action

+= Additionand concatenation

-= Subtraction

*= Multiplication

/=and\= Division

=̂ Exponentiation

&= String concatenation

EQVTheEQVoperatorisreplacedwiththe"="assignmentoperator.

Short-circuitingTheAndAlsoandOrElseoperatorshavebeenaddedtohandleshort-circuiting.All otheroperatorswillremainthesame.Inshortcircuiting,ifthefirstpartofanexpression returnsfalse,thentheremainderoftheexpressionisignored,andfalseisreturned.

DimXasInteger=5

DimYasInteger=6

DimZasInteger=7ret=X>YAndAlsoZ>Y'ReturnFalse,5isnotgreaterthan6

Assignment

VB.NETofferssomecoolnewassignmentoperators. DimintXasInteger

intX=intX+1

Cannowbechangedto: DimintXasInteger

intX+=1

User Defined TypesUserdefinedtypesarenolongersupportedinVB.NET.Theyarereplacedwith structures,whichhavesimilarsyntaxbutmuchgreaterpowerandflexibility.

PublicTypeMyCust strNameasString

strEMailasstring

EndType

Changesto:

PublicStructMyCust

PrivatestrNameasString

PrivatestrEMailasString

EndStruct

Null ValuesNullpropagationisnotsupported.Valuetypesthatarenullarepassedtofunctionsas theDBNulldatatypes.Totestfornullvalues,theIsNullstatementisnolonger

supported.ItisreplacedwiththeDBNullstatement.

IfIsNull(field)then..

Changesto:

IfIsDBNull(field)then…TheIsEmptystatementisnotsupported.InVB6,thevaluesNULLandEmptycouldbe usedtocheckforavariablethathasnotbeeninitializedorforavariablethatcontainsno data.NULLandEmptyarenolongeravalidmeanstocheckforthisinformation,making IsEmptyobsolete.Thenothingkeywordshouldnowbeusedtocheckforthese conditions.

Variable ScopingVariablescanbedeclaredwithinstatementblocksandareonlyavailablewithinthat block.Inthisexample,thevariableintXisonlyavailablewithintheIf…EndIf statement,whereasthevariableintYisavailabletothewholeprocedure.

PrivateSubTest()

DimintYasIntegerIfintY>5then

DimintXasInteger

'DoSomething

Endif

IntX=5

'Causesanerror,intXcannotbeusedoutsideoftheIfblock. intY=10

'OK. intYisnotdecalredwithintheIfblock. EndSub

Variable InitializationVariablescannowbeinitializedto avalueonthesamelineinwhichtheyaredeclared. DimintXasinteger

intX=5

Canbechangedto: DimintXasInteger=5InstantiatingobjectscanalsobedonewiththeNewkeywordonthesamelineasthe objectdeclaration.ThisbehavesexactlyoppositeofVB6,whereitwasfrownedupon becauseofthewayinwhichCOMhadtoensurethatanobjectwascreatedbeforeit coulduseitspropertiesandmethods.

DimcnAsConnection

SetCn=NewConnection

Canbechangedto:

DimcnasSQLConnection=NewSQLConnection'moreefficient

Youcannowdeclaremultiplevariablesonthesameline,withasingletype.Consider thefollowingcode:

Dimstr1,str2,str3asStringInVB6,thevariablesstr1andstr2wouldbeVariantdatatypes,andstr3wouldbe aStringdatatype.InVB.NET,allofthevariableswillbeoftheStringdatatype.

ParmArray VariablesParmArrayvariablesarenotpassedByRefanymore.ParmArraysarepassedby value,andthereceivingfunctioncanmodifythevaluesoftheParmArrayasitwoulda regulararray.

IsMissingTheIsMissingfunctionisnolongersupportedandshouldbereplacedwiththeIsNothingstatement.

Date$andTime$TheDate$andTime$functionsinVB6toreturnastringrepresentationofthecurrent dateortimearereplacedbytheDateStringandTimeStringmethodsinVB.NET.

Atn,Sgn,andSqrTheAtn,Sgn,andSqrfunctionsarereplacedbytheSystem.MathmethodsAtan,Sign,andSqrt.

MsgBoxTheMsgBoxfunctionisreplacedwiththeShowmethod,theMessageBoxclass. MsgBox"VB6isGreat"

Changesto:

MessageBox.Show"VB.NETisGreater"AlthoughMsgBoxisstillsupportedthroughthecompatibilitylibrary,youshouldconsider usingthenewMessageBoxclassessincetheMsgBoxfunctionissimplyawrapper whichcallstheMessageBoxclasses.

ProceduresBecauseVB.NETfullysupportsobject-orientedfeatures,therehavebeencritical changesinprocedurescope,returningvalues,andthetypesofproceduresyoucanuse.

Callingprocedures

Callingprocedures,eithersubsorfunctions,nowrequireparenthesesfortheargument list,eveniftherearenoarguments.

SubTest()

'code EndSub CallTest

Changesto: CallTest()

StaticproceduresStaticproceduresarenolongersupported.Ifyouusestaticprocedures,youshould changethemtoregularsubproceduresanddefinethevariableswithinthestatic procedureasStatic.

StaticSubTest() DimXasinteger

EndSub

Changesto: SubTest()

StaticXasInteger

EndSub

ByVal,ByRef,andAsAnyThedefaultbehaviorofByValandByRefhaschanged.InVB6,thedefaultforpassing parameterswasByRef.InVB.NET,ByValisthedefaultmechanismforpassingvariablestoprocedures.TheAsAnystatementintheDeclarestatementforAPIcalls isnotsupported.

PropertiesThesyntaxfordeclaringpropertyprocedureshasbeenchangedtoaccommodatethe object-orientedfeaturesinVB.NET.Chapter1 4 hasreal-worldexamplesofusing propertiesanddefinesthespecificsyntaxthatyouwillneedtoimplement.

Let,Get,andSetTheLetkeywordisnolongersupported.WhenusingSetandGet,thescopeofthe propertymustbethesameinVB.NET.InVB6,theGetcouldhavebeenscopedas Private,whereastheSetcouldhavebeenscopedasPublic.Thisiseasilynoticed inthewaythatthepropertymustbedeclared.

FriendPropertystrName()AsString

Get

EndGet

Set(ByValValueAsString) EndSet

EndProperty

Defaultproperties

Defaultpropertiesforanyobjectarenolongersupported.InVB6,customclassescould havedefaultproperties,andvisualobjects,suchastextboxes,listboxes,andcombo boxescouldhavedefaultproperties.

strName=Text1'Text1isthenameofatextboxonaform

Me.Caption="HelloWorld"

Changesto:

strName=Text1.Text'mustusetheTextproperty

Me.Text="HelloWorld"Note Defaultpropertiescanstillbecreated.RefertoChapter1 4 for

informationonhowthiscanbeaccomplished.

Control FlowThechangesincontrolflowarenotthatdrastic.ThebiggestchangeistheGoSub keyword,butbecausemostdevelopershavenotusedthissinceVB2.0,itwillnotreally bemissedthatmuch.TheRetur n statementisthenewwaytoreturnvaluesfrom functionprocedures.

While…WendTheWhile…Wendconstructisnolongersupported.ItisreplacedwithWhile…EndWhile. WhileX<5

'CodeWend

Changesto: WhileX<5

'Code

EndWhile

GoSub…ReturnTheGoSubbranchingtoanothersubroutinewithinaprocedureisnolongersupported. Thefollowingcodewillnolongerbevalid.

SubTest

Return EndSub SubTest2

GoSubTest

EndSub

ReturnTheReturnstatementnowreturnscontrolbacktothecallerofthefunction.Ifthe functionisofacertaintype,itcanreturnthevaluebacktothecalleralso.

PrivateFunctionGetNames()asString

DimstrNameasstring strName="SevenOfNine"

GetNames=strName

EndFunction

Changesto:

PrivateFunctionGetNames()asString

DimstrNameasstring strName="SevenOfNine"

ReturnstrName

EndFunction

Forms-based Application ChangesWindowsFormsapplicationshaveacompletelydifferentsubsysteminwhichformsare drawnonthepage,makingitnecessarytoremovesomeofthefunctionalityyoumight beusedtoforpaintinginformationonaform.OneifthebestnewfeaturesinVB.NETis theIDEforaddingmenustoforms,andtheprintingcontrolsthatallowfullprintpreviewinWindowsFormsapplications.

PrintFormThePrintFormmethodisnolongersupported.The.NETFrameworkhasanew printingsubsystem,withfeaturessuchasPrintPreview,whichallowamorerobust handlingofscreenshotsandformsprinting.Circle,Cls,PSet,Line,andPoint

ThesemethodsarenolongersupportedinVB.NET.ThegraphicsmethodsofVB6are replacedwiththeSystem.Drawingnamespace,whichusesthenewGDI+classesfor drawing.

CaptionpropertyTheCaptionpropertyoflabelcontrolsandformsisnolongersupported.TheTextpropertyreplacestheCaptionproperty. Label1.Caption="VB.NET"

Form1.Caption="MyForm"

Changesto:

Label1.Text="VB.NET" Form1.Text="MyForm"

Twipsonforms

Thetwipsmeasurementinformsisreplacedbypixels.

Fonts

FontsinVB6formscouldbeanyfontsupportedbyWindows.WindowsFormssupport onlyTrueTypeorOpenTypefonts.

ControlarraysMultiplecontrolswiththesamename,butadifferentIndexpropertycouldsharethe sameeventproceduresinVB6.InVB.NET,controlscannotbegroupedinarrays,but thesameprocedurecanbeusedformultiplecontrolswiththeHandleskeyword.

Contextmenusandmainmenus

InVB6,amenuaddedtoaformcouldbeusedforboththemainmenuonthetopofa formandacontextmenuthatappearedwiththeright-clickaction.InVB.NET,youcan haveamenubeamainmenuoracontextmenu,butnotboth.

DDE

DDEisnolongersupported.Othermeansofcommunicationbetweenapplicationscanbe accomplishedusingOLE,WebServices,orin-processcomponents.

ClipboardobjectTheClipboardclassreplacestheClipboardobject.

Controlschanges

WhenyoucreateanewWindowsFormsapplication,youwillnoticesomenewand excitingcontrolsintheToolbox.Thecontrolslistedinthissectionarenolonger supported,andtheywillnotappearintheToolbox.

OLEcontrolTheOLEContainercontrolthatallowedtheaddingofOLEobjectstoformsisnolonger supported.

ImagecontrolTheImagecontrolisreplacedwiththePictureBoxcontrolinVB.NET.

LinecontrolTheLinecontrolhasbeenreplacedbyGDI+Drawmethods.

ShapecontrolTheShapecontrolhasbeenreplacedbyGDI+Drawmethods.

Application TypesManyofthetemplatesthatyoumighthavebeenusedtoinpreviousVBversionsno longerexist,andsomeapplicationtypesdonotevenhaveanupgradepath.

Webclasses

Webclassapplicationsarenolongersupported.WebFormsapplicationsshouldbeused towriteWeb-basedapplications.ThepowerandfunctionalityprovidedinusingWeb ServicesandASP.NETapplicationswillgiveyoumuchmoreflexibilitythanprogramming Webclassesapplicationseverdid

ActiveXdocuments

ActiveXdocumentapplicationsarenolongersupported.Youcan,however,write WindowsFormsapplicationsthatrunthroughthebrowserassafecodeandmimic ActiveXdocuments,yetyouwillhavethefullWindowsFormsobjectmodelandcontrols support.

DHTMLapplications

DHTMLapplicationsarenolongersupported.WebFormsapplicationsshouldbeusedto writeWeb-basedapplications.

Usercontrols

UsercontrolscreatedinVB6areusableinVB.NET,butthereisnodesigntimesupport foreditingormodifyingthecontrols.

Propertypages

Propertypagesarenolongersupportedandthereisnoupgradepath.Thisisnotavery bigdeal,sincepropertypageswereusedinActiveXcontrolapplications,andin.NET, youwillbecreatingusercontrolsinsteadofActiveXcontrols.

Data AccessADO.NETisthenewlibraryforaccessingdatafromanysource.Morethanjustan upgrade,itisanactualrewritefromthepreviousversionofADOthatyoumighthave used.Abigissueforupgradingapplicationsistheeliminationofdatabinding.When performinganupgradeusingtheUpgradeWizard,youwillbenotifiedofcodethat cannotbemigratedifyouareusingdatabindingofanysort.

DataBinding,RDO,andADO

DataBindingtoanRDOorADOdatasourceisnolongersupported.Thefollowingcode isobsolete.

Text1.DataField="Customer_Name"

SetText1.Datasource=rs

ThereareextremelypowerfulandmoreadvanceddatabindingcapabilitiesinVB.NET, andtheyarejustimplementeddifferently.

DAO

DataAccessObjectsisnotsupportedinVB.NET.BecauseyoucanaccessdatathroughADO.NET,thelossofDAOisnotearthshattering.Itwilljustmeanthatyouneed toconvertDAOcodetoADO.NETcode.

DebuggingVisualBasichasalwaysbeenattheforefrontinsupportfordebugging.The Debug.Printmethodhasbeenreplaced,butthisisminorcomparedtoallofthenew featuresthatmakedebuggingeasierthanever.

Debug.PrintDebug.PrintisreplacedbytheDebug.WriteortheDebug.Writelinemethods. TheDebugclassprovidesacompletesetofmethodsandpropertiesthathelpdebug yourcode.

Debug.PrintErr.number

Changesto:

Debug.WritelineErr.Number'includesLineFeed

Or

Debug.WriteErr.Number'doesNOTincludeLineFeed

Debug.AssertTheDebug.Assertmethodisnolongersupported.ItisreplacedwiththeAssertandFailmethodsoftheDebugclass.

PartII:TheVB.NETProgrammingLanguageChapter 3 :Object-OrientedProgrammingandVB.NET Chapter 4 :HelloWorldChapter 5 :DataTypes,Variables,andOperatorsChapter 6 :ArraysChapter 7 :ConditionalLogic

Chapter3:Object-OrientedProgrammingandVB.NETIn This Chapter

EncapsulationInheritancePolymorphism

EncapsulationEncapsulationExamplePublicClassContact

Private_FirstNameAsStringPrivate_LastNameAsStringPrivate_EmailAsString

PublicPropertyFirstName() Get

Return_FirstName

EndGetSet(ByValValue)

_FirstName=ValueEndSet

EndProperty

PublicPropertyEmail() GetReturn_Email

EndGetSet(ByValValue)

_Email=ValueEndSet

EndProperty

PublicPropertyLastName() Get

Return_LastNameEndGet

Set(ByValValue)_LastName=Value

EndSetEndProperty

PublicReadOnlyPropertyNameHi() Get

Return_FirstName.ToUpper&""&_LastName.ToUpper

EndGet

EndProperty

PublicReadOnlyPropertyNameLo() Get

Return_FirstName.ToLower&""&_LastName.ToLower

EndGet

EndProperty

PublicReadOnlyPropertyNameProper() Get

ReturnStrConv(_FirstName,VbStrConv.ProperCase)&""_

&StrConv(_LastName,VbStrConv.ProperCase) EndGet EndProperty

EndClass

InheritanceInheritanceistheabilitytocreatenewclassesbasedonanexistingclass.Thenewclass inheritsalltheproperties,methods,andeventsofthebaseclass,andcanbecustomized withadditionalpropertiesandmethods..Aderived classisaclassbasedonabaseclass.TheInheritskeywordusedinsideaclass derives,orinherits,thefunctionalityofthatclass.In.NET,allclassesareinheritablebydefaultunlesstheyaredefinedwiththeNotInheritablekeyword.IntheContactclassyoucreatedearlier,theclasswas definedas

PublicClassContact

Tomaketheclassnotinheritable,youwoulddefineitasfollows:

PublicNotInheritableClassContactBydefiningtheContactclassasNotInheritable,itdoesnotaffecttheclient-side declaration.Itdoes,however,affecthowtheclasscanbeusedinotherclasses.An instanceofContactcanbecreatedwiththeNewkeyword,butaclasscannotusethe InheritskeywordtoimplementtheContactclassfunctionality.

TheexactoppositeoftheNotInheritablekeywordistheMustInheritkeyword.IfyoudefineaclasswiththeMustInheritkeyword,itcannotbecreatedwiththeNew keyword.Thebaseclasscanonlybeinheritedfromotherclasses.IftheContactclass wasdefinedasMustInherit,asthefollowingcodedemonstrates:

PublicMustInheritClassContact

Thenthefollowingcodefromtheclientapplicationwouldbeinvalid:

DimcasNewCustomerThismeansthatinordertogettoanyofthemembersintheContactclass,youneedto createanotherclass,andusingtheInheritskeyword,inherittheContactclass.

PolymorphismPolymorphismisthecapabilitytohavemethodsandpropertiesinmultipleclassesthat havethesamenameandcanbeusedinterchangeably,eventhougheachclass implementsthesamepropertiesormethodsindifferentways.

Thefollowinglistgetsyouuptospeedonsomeofthesyntaxyoucanusewhen implementingpolymorphism:Overridable:Allowsapropertyormethodinaclasstobeoverriddenina derivedclass.Overrides:OverridesanOverridablepropertyormethoddefinedinthe baseclass.NotOverridable:Preventsapropertyormethodfrombeingoverriddenin

aninheritingclass.PublicmethodsareNotOverridablebydefault.MustOverride:Requiresthataderivedclassoverridethepropertyor

method.WhentheMustOverridekeywordisused,themethoddefinition consistsofjusttheSub,Function,orPropertystatement.Noother statementsareallowed,andspecificallythereisnoEndSuborEnd Functionstatement.MustOverridemethodsmustbedeclaredin MustInheritclasses.

Chapter4:HelloWorldIn This Chapter

AHelloWorldapplicationusingWindowsFormsAHelloWorldapplicationusingWebForms

Withthe.NETFramework,youcancreatethreetypesofapplications—Windows applications,Webapplications,andConsoleapplications.WindowsFormsprovideuserswithabasicsetofclassestocreateagraphicaluser interfaceforWin32desktopapplications.Theyusethesamedrag-and-droptechniqueto createarichuserinterface.Ontheotherhand,WebFormsprovideabrowser-based userinterface.WebFormsalsoallowyoutocreateauserinterfacebyusingthedrag- and-dropmethod.Inadditiontothegraphicaluserinterface(GUI)applications,the.NETFrameworkalso allowsdeveloperstocreatecharacteruserinterface(CUI)applications.CreatingCUI applicationsispossiblethroughConsoleapplications.

Creating a Windows Forms ApplicationWindowsForms,whicharebasedonthe.NETFramework,allowyoutodevelop Windowsapplications.YoucandevelopVisualBasic.NETWindowsapplicationsby usingtheWindowsFormsDesignerprovidedwithVisualStudio.NET.VisualStudio.NETprovidesacommonIntegratedDevelopmentEnvironment(IDE)fordevelopingapplicationsinall.NETprogramminglanguages.

CreatingaWindowsApplicationproject

ThefirststeptocreateaWindowsFormsapplicationistocreateaVisualBasicWindowsApplicationproject.Todoso,followthesesteps.

1. SelectFile New ProjecttoopentheNewProjectdialogbox.Tip Alternatively,youcanusehotkeystoaccessdifferentoptions.Inthe

precedingstep,pressAlt+FtoopentheFilemenu.Then,pressNto opentheNewsubmenu.Finally,toopentheNewProjectdialogbox, pressP.

YoucanalsoopentheNewProjectdialogboxbypressingCtrl+Shift+N.

2. FromtheProjectTypespane,selectVisualBasic.3. FromtheTemplatespane,selectWindowsApplicationtocreatea

VisualBasicWindowsApplicationproject.4. IntheNamebox,enterthenameoftheproject.IntheLocationbox,

specifythedirectorywhereyouwanttostoretheproject.Todoso, youcanusetheBrowsebutton.Inthiscase,specifythenameofthe projectasWinHelloWorldandthelocationasC:\VBProjects.Atthis stage,theNewProjectdialogboxappears,asshowninFigure4 - 1 .

Figure4-1: TheNewProjectdialogbox.AftertheVisualBasicWindowsApplicationprojectiscreated,VisualStudio.NETdisplaystheinterface,asshowninFigure 4 - 2 .

Figure4-2: AsampleWindowsApplicationproject.Asyoucanseeinthefigure,theSolutionExplorerwindowisdisplayedtotheextreme rightoftheVisualStudio.NETwindow.TheSolutionExplorerwindowcanconsistof multipleprojects,whichcouldbecreatedinmultiplelanguages.WhenaWindows Applicationprojectiscreated,theForm1.vbfileisselectedbydefault,andtheformis displayedinDesignmode.

UsingWindowscontrolsVisualStudio.NETprovidesaToolboxthatyoucanusetodesigntheuserinterfacefor yourapplications.YoucandisplaytheToolboxbyselectingToolboxfromtheView menu.Bydefault,theToolboxisplacedtotheextremeleftofthewindow.TheToolbox opensonlywhenyoumoveyourmouseoverit.Thisfeatureiscalledautohide.

TheToolboxcontainsdifferentcontrols,categorizedaccordingtotheirfunctionality.For example,thestandardWindowscontrols—suchasLabel,Button,andTextBox—are categorizedunderWindowscontrols.

Figure 4 - 3displaysthePropertieswindowwhenaLabelcontrolisselected.Asyoucanseeinthefigure,theDefaultpropertyoftheLabelcontrolishighlighted.

Figure4-3: ALabelcontrolisselectedinthePropertieswindow.

InthePropertieswindow,youcanviewthepropertiesofaselectedobjectina categorizedoranalphabeticalmanner.TocreateasimpleHelloWorldWindowsapplication,createaformthatcontainsaLabel andaButton.Specifytheproperties,asdescribedin Table4 - 1 .Table4-1:PropertiesofControlsintheSampleWindowsForm

Control Property Value

Label Text

Name

ForeColor

Font.Bold

TextAlign

Welcometo Windows Forms

MessageLabel

BlueTrue

TopCenter

Button Text

Name

Forecolor

Font.Bold

SayHello

HelloButton

Blue

TrueFigure 4 - 4 showsthesampleform.

Figure4-4: AsampleformfortheHelloWorldWindowsapplication.

UsingtheCodewindowAfteryoudesignaform,thenextstepiswritingthecodetoprovidethedesired functionalityforthecontrols.YouwritethecodeintheCodewindow,whichyoucan openbyselectingCodefromtheViewmenuorbypressingF7.YoucanalsoopentheCodewindowbydouble-clickingthebuttoncontrolorright-clickingtheformandselectingViewCode.TheCodewindowalreadycontainssomeVisualBasiccode,asshowninFigure 4 - 5 .

Figure4-5: TheCodewindowdisplayingtheVisualBasiccode.ThetopoftheCodewindowcontainstwodrop-downlists:ClassNameandMethod Name.TheClassNamelistcontainsthenamesofalltheclassesinthecurrentproject. Currently,theClassNamelistdisplaysForm1[WinHelloWorld].TheMethodNamelist containsthenamesofthemethodsoftheclassthatisselectedintheClassNamelist. Currently,theMethodNamelistdisplays[Declarations].

ThefirstlineoftheCodewindowdisplaysthefollowingcode: PublicClassForm1

InheritsSystem.Windows.Forms.FormTheprecedingcodeindicatesthatForm1isaclassthatisinheritedfromtheFormclass. TheFormclassisincludedintheSystemnamespaceofthe.NETFramework. System.Windows.Forms.FormindicatestheclasshierarchyintheSystemname- space.Namespacesareawaytogrouptherelatedclassestogether.Theyprovideproperorganizationofclasses,sothattheyareconvenienttouse.

Creating a Web Forms ApplicationWebFormsisafeatureofASP.NETthatcreatesrichWebapplications.ASP.NETisa programmingframeworkusedtodevelopWebapplications,andisapartofthe.NET Framework.WebFormsprovideRapidApplicationDevelopmenttechniquesthatenable youtocreatearichuserinterfaceforWebapplications.WebFormsconsistofapagethatisusedtodesigntheuserinterfaceandacodefile thatprovidesfunctionalitytotheuserinterface.Thepageconsistsofafilecontaininga markuplanguage,suchasHTMLorXML,andcontrols.Apagefilehas.aspxasits extension.

ThefunctionalitytorespondtouserinteractionswiththeWebFormspagesisimplementedbyusingprogramminglanguages,suchasVisualBasicandVisualC#.Youcanimplementthefunctionalityinthe.aspxfileorinaseparatefilewritteninVisualBasic.NETorC#.Thisseparatefile,calledtheCodeBehindclassfile,has.aspx.csor.aspx.vbasitsextension.Thus,aWebFormspageconsistsofapage(an.aspxfile)andacodebehindclassfile(an.aspx.vbfileoran.aspx.csfile).CreatingaWebApplicationproject

Note ThefirststeptocreateaVisualBasicWebFormsapplicationisto createaWebApplicationproject.Todoso,followthesesteps:

1. SelectFile New ProjecttoopentheNewProjectdialogbox.2. FromtheProjectTypespane,selectVisualBasic.3. FromtheTemplatespane,selectASP.NETWebApplicationtocreate

aVisualBasicWebApplicationproject.4. IntheNamebox,enterthenameoftheproject.IntheLocationbox,

specifythenameofaWebserverinwhichyouwanttostorethe project.Inthiscase,specifythenameoftheprojectas WebHelloWorldandthelocationashttp://<computername>/. Here,<computername>intheLocationboxrepresentsthenameof thecomputerthathoststheIISServer.

Note YoumusthaveanIISServerinstalledonthedevelopmentcomputer.Otherwise,youcannotcreateWebapplications.

AftertheVisualBasicWebApplicationprojectiscreated,VisualStudio.NETdisplays thenumberoffilesintheSolutionExplorerwindow.TheWebForm1.aspxisselected bydefaultandisdisplayedinthedesigner.

UsingtheWebFormsServercontrols

AfteryoucreateaWebApplicationproject,youcandesigntheuserinterfaceoftheWeb FormspagebyusingtheWebFormsdesignerprovidedbyVisualStudio.NET.The designerprovidesaToolboxthatcontainsvariousWebFormsServercontrolsthatcan beaddedonthepagetodesignarichuserinterface.TheseServercontrolsdifferfrom theusualWindowscontrols.UnliketheWindowscontrols,theWebFormsServercontrolsworkwithintheASP.NETFrameworkandareavailabletobeprogrammedatthe serverend.ThewaycontrolsareaddedtotheWebFormspagesissimilartothewayyouaddthem totheWindowsForms.Youcanaccessorassignthepropertiesofacontrolinthe PropertieswindowthesamewayasyoudowithWindowsForms.TocreateasimpleHelloWorldWebapplication,addaLabelandButtontothepage.Thensettheproperties,asshownin Table4 - 2 .Table4-2:PropertiesofControlsintheSampleWebForm

Control Property Value

Label TextID

ForeColor

Font.Bold

WelcometoWebForms

MessageLabel

Blue

True

Button TextID

Forecolor

Font.Bold

SayHello

HelloButton

Blue

True

TheformshouldappearasshowninFigure4 - 6 .

Figure4-6: AsampleWebFormspage.

UsingtheCodewindow

Afterthevisualcomponentisdesigned,youcanusetheCodeBehindfiletoimplement thedesiredfunctionalitywiththeuserinterface.YoucanviewtheCodeBehindfileby selectingCodefromtheViewmenuorbypressingF7.

Chapter5:DataTypes,Variables,andOperatorsIn This Chapter

DatatypesVariablesTypeconversionStructuresNumericparsingSystem.StringclassOperators

Data Types and VariablesAvariableisapointertoablockofmemorythatstoresinformation.Theinformationthat isstoredinavariableisofacertaindatatype.Inallprogramminglanguages,youdefine areal-worldobjectthatreferstosometypeofinformationthatyouneedtoworkwith. The.NETFrameworkusestheconceptofCommonLanguageSpecification(CLS)compliantdatatypes.Thismeansthatany.NETcompileryouareusingmustatleast allowforcertaindatatypes.Ifitdoesnot,thecompilerisnotCLScompliantand,inturn, thelanguagecannotbeconsideredaCLR-compliantlanguage.

VB.NETdatatypesInVB.NET,alldatatypesallowedareCLS-compliant.The.NETFramework,alldata typesarederivedfromtheSystemnamespace.Eachtypeisdefinedasastructure withintheSystemnamespace.Becauseallobjectsin.NETarederivedfromthebasetypeSystem.Object,thedatatypesyouareusingareactuallyclassesandstructures derivedfromtheSystem.Objecttype.Allclasseshavemembers,properties,and fields;thedatatypesdefinedintheSystemnamespacearenodifferent.Table5 - 1 lists thedatatypes,theCLStypeandtheallowablerangesforeachtypedefinedinthe Systemnamespace.

AnimportantthingtonoticeforVBdevelopersisthedifferencesbetween.NETdata typesandpre-.NETdatatypes.InVB6,theShortdatatypedidnotexist,andthe Integerdatatypehadarangeof–32,768to+32767.In.NET,theShortdatatypereplacestheIntegerdatatype,andtheIntegerdatatypereplacestheLongdata type.ThenewLongdatatypeisa64-bit,8-bytenumber,averylargenumber.Table 5 - 2summarizesthedatatypechangesinVB.NETfrompreviousVBversions.

Table5-1:VB.NETDataTypes

Type CLSType Bytes Value

Boolean System.Boolean 4 TrueorFalse

Byte System.Byte 1 0to255unsigned

Char System.Char 2 0to65,535unsigned

Date System.DateTime 8 January1,1toDecember31,9999

Decimal System.Decimal 12 +/–79,228,162,514,264,337,593,950,335withnodecimalpoint.

+/–7.9228162512264337593543950335with28placestotherightof thedecimalpoint.

Thesmallestnonzeronumber wouldbea1inthe28thposition totherightofthedecimalpoint.

Double System.Double 8 1.797693134862231E308to–4.94065645841247fornegative valuesto4.94065645841247to1.797693134862231E308for positivevalues

Integer System.Int32 4 –2,147,483,648to2,147,483,648

Long System.Int64 8 9,223,372,036,854,775,808to9,223,372,036,854,775,807

Short System.Int16 2 –32,768to32,767

Object System.Object 4 Anobjectcanholdanyvariable type

Single System.Single 4 3.402823E38to–1.401298E-45 fornegativevaluesto1.401298E-45to3.402823E38forpositive values

String System.String 10+ (2*Leng th)

0to2billionUnicodecharacters(approximately).

User Defined Type

(structure) System. ValueT ype

Sumofthesizeofitsmembers

Eachmemberofthestructure hasarangedeterminedbyits datatypeandindependentofthe rangesoftheothermembers

Table5-2:DataTypeChanges

DataType PreVB.NET

VB.NET

System.Int16 Integer Short

System.Int32 Long Integer

System.int64 Didnot exist

Long

Variant Variant Doesnotexist

Currency Currency Decimal

Date Date Long

VariabledefaultsWhenyoudeclareavariableofatypewithoutassigningavaluetoit,thevariablehasa defaultvaluebasedonthetypeofvariableyouhaveassignedasthetype.Thefollowing arethedefaultvaluesfordifferenttypes:

Numbers:0(zero) Boolean:False String:Nothing Object:Nothing Date:12:00:00AM

OptionExplicitstatementTheOptionExplicitstatementforcesyoutodeclarevariablesbeforeyoureference theminyourcode.ThisstatementworksthesamewayasitdidinpreviousVBversions. InVB.NET,youcansettheOptionExplicitstatementontheprojectlevel,inthe propertiesdialogbox,oryoucanusetheOptionExplicitstatementatthetopof yourclassfilesormodules.TheusagefortheOptionExplicitstatementisas follows:

OptionExplicit{On|Off}IfyouspecifyOptionExplicitOnandattempttoreferenceavariablethatisnot declared,theIDEnotifiesyouoftheerrorasyouarecoding.

ConstantsAconstantallowsyoutouseafriendlynameforavariablevaluethatdoesnotchange throughouttheexecutionofyourapplication.ConstantsinVisualBasic.NETactexactly astheydidinpreviousversions.Todeclareaconstant,youusetheConstkeyword withinaprocedureoratthedeclarationssectionofyourclassesormodules.Constants canbedeclaredwiththescopeofPrivate,Public,Friend,Protected,or ProtectedFriend.ThefollowingistheusageoftheConststatement.

[Public|Private|Friend|Protected|ProtectedFriend]

Constconstantname[Astype]=expressionWhenyoudeclareaconstant,youmustdeclareitasacertaintype.ConstantscanbedeclaredasBoolean,Byte,Char,DateTime,Decimal,Double,Integer,Long, Short,Single,orStringdatatypes.Inthefollowingcode,youaredeclaringseveral constantsandthenusingthemintheprocedurewithinthemodule.

ModuleModule1

PrivateConstBillsSalaryAsDouble=1000000000

PrivateConstMySalaryAsByte=100

PrivateConststrMsgAsString="TryAgainPlease"

PrivateFunctionTest_Salary()AsBoolean

IfMySalary>BillsSalaryThen

Console.WriteLine(strMsg) EndIf

EndFunction

EndModule

VariablescopeThescopeofavariablecanbedeclaredasPrivate,Public,Static,Shared, Protected,orFriend.Hereissomefamiliarlookingcode,declaringdifferentvariable typeswithdifferentscopes:

Publicv,basDouble

Statici,sasLongDimc,o,o,lasString

Privaten,e,a,t,oasInteger

PrivatevariablesPrivatevariablesareavailabletothemodule,class,orstructureinwhichtheyare declared.AswithpreviousVisualBasicversion,DimandPrivateactinthesame manner,withtheexceptionthatthePrivatekeywordcannotbeusedtodeclare variableswithinasubprocedureorfunction.HereisanexampleofhowyoucouldusePrivateandDimwithinaclass: PublicClassVar1

PrivateSharedintJasInteger

SharedSubMain()

DimintYasInteger=100

CallDoSomething

Console.Writeline(intJ)

'returns100

Console.Writeline(intY) EndSub

PrivateSharedSubDoSomething() IntJ=100

EndSub

EndClassInthisexample,intJissharedthroughoutallmembersoftheclass,sinceyouusedthe PrivateShareddeclaration.WhenyoudeclaredintYwithintheSubMain procedure,thescopeofthatvariableistheSubMainprocedureonly;anyattemptto useitoutsideofSubMainresultsinanerror.ThisbehaviorisidenticaltopreviousVB versions.Thefollowingcodeisinvalid:

SubEatDinner()asBoolean

PrivateintXasinteger=100

EndSub

Privateisnotallowedtodeclarelocalvariableswithinasubprocedure.

PublicvariablesPublicvariablesareavailabletoallproceduresinallclasses,modules,andstructuresin yourapplication.Itisimportanttonotethatinmostcases,methodandvariable declarationispublicbydefaultinVB.NET.InpreviousversionsofVisualBasic,the defaultwasprivate,soyoumaywanttoconsiderwhereyouneedtoaccessmethodsandvariablesbeforedeclaringeverythingaspublic.Thefollowingexampledemonstratestheuseofapublicvariableusedinmultipleclasses.NoticethatbothintXandintYare inthePublicscope,andareaccessibletotheclassesinthemodule.

ModuleModMain

'Thisisourpublicvariable,availabletoeverything

PublicintX,intYAsInteger

PublicClassDog

SubX()

intX=100

EndSub

SubY()

intY=300

EndSub

EndClass

PrivateClassAnimals

SubZ()

intX=500

EndSub

EndClass

EndModule

StaticvariablesStaticvariablesarespecialvariabletypesthatretaintheirvalueswithinthescopeofthe methodorclassinwhichtheyaredeclared.Astaticvariableretainsitsvalueuntilthe valueofthevariableisreset,oruntiltheapplicationends.

StaticintSAsInteger=100

SubTest()

intS=intS+1

IfintS=105Then intS=100

EndIf

EndSubInthisexample,eachtimethesubisexecuted,thevalueofintSisretaineduntilthe valuereaches105,thenthevalueofintXisresetto100,andthishappensforeveruntil theapplicationends.Staticvariablescanonlybedeclaredattheprocedurelevel.Ifyou attempttodeclareavariableattheclassormodulelevel,yougetacompilererror.

SharedvariablesSharedmembersareproperties,procedures,orfieldsthataresharedbyallinstancesof aclass.Thismakesiteasytodeclareanewinstanceofaclass,butmaintainashared, publicvariablethroughoutallinstancesoftheclass.Hereissomecodethatexplains this:

ModuleModMain

ClassAnimal

PublicSharedEyesAsBoolean

PrivatestrDescAsString

PropertyFriendly()AsString

Get

Friendly=strDesc

EndGet

Set(ByValValueAsString)

strDesc=Value

EndSet

EndProperty

EndClass

SubMain()

DimCatAsAnimal=NewAnimal()

DimRatAsAnimal=NewAnimal()

Cat.Friendly="Yes" Cat.Eyes=True

Rat.Friendly="No"

console.WriteLine(Rat.Eyes)

EndSub

EndModuleTheresultwrittentotheconsoleisTrue.BecauseyoudeclaredEyesasshared,you don'thavetosetitforeachinstanceoftheclasscreated.Thevariableisshared throughoutallinstancesoftheclass.Thiscouldalsocauseyouproblemsifyouareexpectingvariablestobeinitializedtoemptyornullwhenaclassisinstantiated,soyoushouldusecautionwhenimplementingsharedvariables.

ProtectedvariablesProtectedvariablesareonlyavailabletotheclassinwhichtheyaredeclared,orclasses thatderivefromthesameclass.Inthefollowingcode,thevariableXisavailableonlyto theclassinwhichitisdeclared.TheattempttoaccessitintheClassBresultsinan error.

ModuleModule1

ClassA

'Declareprotectedvariable

ProtectedXAsInteger

PrivateFunctionTestX()AsBoolean

'Setvalueofprotectedvariable

X=5

EndFunction

EndClass

ClassB


X=5

EndFunction

EndClass

EndModule

FriendvariablesFriendvariablesareaccessiblefromanyclassormodulewithintheassemblythatthey aredeclaredin.Inthefollowingcode,afriendvariableisdeclaredatthemodulelevel, andthevariableisavailabletoallclasseswithinthismodule.

ModuleModule1

'DeclareFriendvariable

FriendXAsInteger

ClassA


'Setvalueofprotectedvariable

X=5

EndFunction

EndClass

ClassB


X=5

EndFunction

EndClass

EndModule

Type ConversionDatatypeconversioninVB.NETisverysimilartoearlierVBversions.Whenyouconvert types,youcanusebuilt-infunctionstoconvertfromonetypetoanother.Therearetwo typesofdataconversion:wideningandnarrowing.

Widening:Conversionisabletomaintaintheoriginaldatavalue,withoutdataloss.

Narrowing:Conversionattemptstoconvertdatafromalargertypetoa smallertype(inbytesorprecision)thatmaynotbeabletomaintainthe originalvalue.

Anexampleofnarrowingconversionwouldbethefollowing: DimXasSingle=123.45

DimYasInteger

Y=X

Table5-5:AllowableTypeConversionRanges

DataType Allowable Conversi onRange

Byte Byte, Short, Integer, Long, Decimal, Single, Double, Object

Short Short, Integer, Long, Decimal, Single, Double, Object

Integer Integer, Long, Decimal, Single, Double, Object

Long Long, Decimal, Single, Double, Object

Decimal Decimal, Single, Double, Object

Single Single, Double, Object

Double Double, Object

Char Char, String, Object

DerivedTypes Any base type from whichit is derived

Inthiscase,thedecimalplacesarelost;anintegervaluedoesnothaveprecision,soit cannotholdnumberstotherightofthedecimalplace.InVS.NET,ifyouturnOption StricttoONtheapplicationdoesn'tcompileunlessyouperformanexplicitconversion betweenthedatatypes.Thisisagoodthing;thecompilerinallearlierVBversionsdid notofferthiscatch,andbugswereeasilyintroducedduetoconversionerrors.Table5 - 5liststheallowablerangesforwideningwhenconvertingdatatypes.

Table5-5:AllowableTypeConversionRanges

DataType Allowable Conversi onRange

AnyType Any Interface theType implement s

Built-intypeconversionfunctions

Thefollowingbuilt-inconversionkeywordsarestillavailableinVB.NET:

CBool,CByte,CChar,CDate,CDbl,CDec,CInt,CLng,CObj,

CShort,CSng,CStrandCType.

StructuresInpreviousVBversions,theUserDefinedType(UDT)wasanextremelyusefulwayof definingyourowntypes.Iuseditallthetimetostoreglobaldata,andtostorerowsfrom adatabasethatweremostlystatic.AnexampleofaUDTinVB6wouldbe:

PublicCustomerasType strNameasstring

strAddressasstring strEmailasstring

EndType

PublicCCustomer()asCustomerThevariableCCustomerwasdeclaredasanarrayoftypeCustomer.InVB.NET, StructuresreplaceUDTs.Thisisnotatrivialnamechange.Structuresofferincreased functionalityandobject-orientedfeatures.MyexampleoftheCustomertypewouldbe convertedtoastructureinVB.NETlikethis:

StructureCustomer

PublicstrNameasstring

PublicstrAddressasstring

PrivatestrTaxIDNumberasstring

EndStructure

PublicCCustomerasCustomerBothexampleslooksimilar,andtheyare.It'swhathappensunderthehoodthatgivesus theadvantagesofstructuresinVB.NET.Youcandefineastructureasawaytogrouplikedata.Structuresaredeclaredwiththe Structure…EndStructurestatement.Betweenthedeclarations,youlistyour variableswiththePublic,Private,Protected,orSharedscope.Insideofa structure,variablesdeclaredwithDimarePublicbydefault;thisistheexactopposite behaviorinclassesandmodules.Whenyoudeclareavariabletobeaninstanceofa structure,allofthestructure'smembersareinitializedautomatically,whichmeansyou donotneedtoinitializeindividualmembersofastructure.Whenyoudecidethatyou needtousethestructure,youdeclareavariableasthetypeofthatstructure.Youcan declarethevariableinoneoftwoways:

DimvarnameasStructureName

Dim varnameasStructureName=NewStructureName

Note Structuresarevaluetypes,notreferencetypes.

Afteryoudefineastructure,anddeclareavariabletoreferencethestructure,youcan usethefollowingsyntaxtoreferencethemembersofthestructure:

CCusotmer.strAddress="1234MainStreet"

CCustomer.strName="BillGates"

Table5-9:ArithmeticOperators

Operator Action

+ Addition

- Subtraction

* Multiplication

/ and\ Division

% Modulo

^ Exponentiation

OperatorsTheoperatorscanfallintoone ofthesecategories:arithmetic,assignment,bitwise,comparison,concatenation,and logical.Thebasicpurposeofanoperatoristoassignorretrievevaluesbasedonexpressionsor statements.Inthefollowingexample,youareassigningthevalueofthevariableXequaltowhatever thevalueofYmightbe.Thisisanexampleofanassignmentoperator;youareassigning thevalueofoneexpressiontothevalueofanother.

X=YThefollowingisanotherexampleofanassignmentoperator,exceptthatinthiscase, youareevaluatingthereturnvalueoftheSquareItfunction,whichisastatement,and assigningthevaluefromthefunctioncalltothevariableintX.

X=SquareIt(5)

Inthenextexampleyouarecombiningtwostringswiththeconcatenationoperator, settingthevalueofthevariableonthelefttotheevaluationofthestatementontheright sideoftheequals(=)sign.

TheCarIWishIHad="Mercedes"&"Benz500SL"

Arithmeticoperators

AdditionoperatorThe+,oradditionoperator,sumsorconcatenatestwoexpressions.Concatenationis discussedalittlelaterinthischapter,aswellaswhatyouhavetolookoutforwhen usingthe+operator.Theusageforadditionoperatorisasfollows:

Result=Expression+Expression

Thefollowingexampleshowsthesimplestformoftheadditionoperatorpossible,adding twovaluestogether:

DimintXAsInteger intX=intX+5

Console.Writeline(intX.ToString)ThevariableintX,declaredasintegervalue,hastheinitialvalueofzero.Toadd5to thevalueintX,yousimplyusetheadditionoperator(+)andtheassignmentoperator (=)toderivethenewvalue.Thefollowingcodeaccomplishesthesamething:

Dim intX As Integer Dim intY As Integer

intY=intX+5

Console.Writeline(intY.ToString)TheonlydifferenceisthatyoucreateanewvariablecalledintYtoholdthevalueof intXplusthenumber5.Creatingvariablesjustfortheheckofitisnotefficient,soifthe valueofintXhasthesolepurposeofbeinganintegerwith5addedtoit,thenusethe firstexampleasaguide.NewtoVisualBasic.NETarespecialassignmentoperators thatperformanactiononavariable,suchasaddition.Theprecedingadditioncodecan alsoberepresentedas

DimintXAsInteger intX+=5

Console.Writeline(intX.ToString)Assignmentoperatorsarecoveredinmoredetailinthenextsection .Eventhoughthey looklikemathematicaloperators,theyareactuallynot;becauseyouareusingtheequals

sign(=),itindicatesanassignment.Inthepreviouscode,youdeclaredvariablesofthe typeInteger,whichthecompilerunderstood,andaddedthevaluestogether.Consider thisexample:

DimintXAsInteger=10

MessageBox.Show(intX+"9")Theresultinthisexampleis109.Additiondidnotoccur.Becausethevalueof"9"is enclosedindoublequotes,thecompilerunderstandsitasastringdatatype,sothe valuesareconcatenated,andnotadded.Ifyouarenotsureofthetypeofdatayouare dealingwith,andyouneedtomakesurethatadditionoccurs,usetheconversion functionsdiscussedearlierinthechapter.Thefollowingcodetakescareofthisproblem:

DimintXAsInteger=10

MessageBox.Show(intX+CInt("9"))

Understandingthedatayouaredealingwithisveryimportant;asyoucansee,the resultscanvarysignificantlyifyouarenotcareful.Thefollowingrulesapplywhenusing theadditionoperator:

Additionoccursifbothexpressionsareofthesamenumericdatatype. Concatenationoccursifoneorbothexpressionsarestrings. If OptionStrictisON,implicitconversionbetweentypesisnot

allowed,sothepreviousexampleusingCIntthrowsanexception, andneitherconcatenationnoradditionoccurs.

If OptionStrictisOFF,implicitconversionisallowed,andthe expressionsareaddedifimplicitconversionisused.Thisconversion canbetonumericorstringdatatypes,andtheresultvariesbasedon theconversionoftheexpression.

Narrowingorwideningconversionsoccurifthenumericdatatypesusedinexpressionsaredifferentthanthenumericdatatypeofthe result.

Thefollowingcoderoundsupanexampleofusingtheadditionoperand,andtheresults thatcanoccur,assumingthedefaultOptionStrictofOFF.Theinlinecommentsin thecodecanhelpyouunderstandwhatwe'retryingtoaccomplish.

DimdblXAsDouble=6.54

DimdblYAsDouble=9.32

DimstrXAsString= "6" DimstrYAsString= "5"

DimintXAsShort

intX=CShort(strX)+CShort(strY) MessageBox.Show(intX)

'ResultisShortDataTypewithavalueof11

MessageBox.Show(strX+strY)

'ResultisStringDataTypewithavalueof65 intX=dblX+dblY

MessageBox.Show(intX)

'Resultis16,Integerdatatypecannothaveadecimalplace,

'sothenarrowingconversiontakesplace strX=dblX+dblY

MessageBox.Show(strX)

'Resultis15.86,Doubledatatypesareadded,sincetheyare

'ofthesametype,andtheStringwillholdtheresultwithout

'anerror

strX=dblX.ToString+dblY.ToString

MessageBox.Show(strX)'Resultistheconcatenationof6.549.43,sincetheToString

'converttheDoublevaluestostrings,allvaluesarestrings,

'andconcatenationoccurs

SubtractionoperatorThesubtractionoperator(–),indicatingsubtractionornegations,returnsthedifference betweentwonumbersorexpressions,oritnegatesanumericvalue.Herearethetwo possibleuses:

result=number1—number2 variable=-number

Youhavebeendoingsubtractionsinceyouopenedyourfirstbankaccountandtheteller gaveyouthelittleaccountbalancebooklet.Therearenorealgotchasherewiththeway theoperatorworks.

DimintXasInteger

DimintYasInteger=500 intX=intY—100Inthisexample,youaresubtracting100fromthevalueofintY,whichis500,and assigningthisvaluetothevariableintX.Inthiscase,thenewvalueofintXis400.If intYislessthan100,thevaluereturnedtointXisnegative.Soifthecodewas modifiedto

DimintYasInteger=5

theresultwouldnowbe–95.

Tosimplynegateavalue,youcanassignittothenegativevalueofitselfortoanew variable.Youcouldrefertothe—operatorastheunarynegationoperatorinthiscase,as inthefollowingexample:

DimintXasInteger=100 intX=-intX

Whenusingsubtraction,makesurethatthedatatypesinusesupportthetypeof operationthatyouareattemptingtoaccomplish.Thisrulestandsforalloperators.For example,ifyouarebalancingyourcheckbook,andtheresultvariableisdeclaredasan integerdatatype,thenyouaredefinitelylosingmoney,becausethedecimalplacesare gettinglostintheprocess.

DimdblVal1AsDouble=100.54

DimdblVal2AsDouble=23.45

DimintYAsInteger

intY=dblVal1-dblVal2

MessageBox.Show(intY)'Returns77

MessageBox.Show(dblVal1 -dblVal2)'Returns77.09

MultiplicationoperatorThemultiplicationoperator(*)multipliestwonumbersandreturnsaresult. Theusageis

Result=Number1*Number2

5*5=25

Whenyouuseacalculator,thelogicalprocessistakingthetwonumbersyouwantto multiplyandthenpresstheequalssign.Whenyoucode,youdotheopposite—you declarethevariable,andsetthatvaluetotheresultingvalueoftheoperationyouare attemptingtoaccomplish.

DimintXasInteger=5

DimintYasInteger=5

DimintResultasInteger intResult=intX*intYInthisexample,youmultiplytwovariablesandassignthevalueofintResulttothe resultofyourmultiplication.Ifyoudidthistheoppositeway,asyouwouldtypeitintoa calculatororaddingmachine,thevalueofintResultwouldbezero.

intX*intY=intResultintResultisinitializedaszero,andbysettingthevalueofintX*intYtothevalue ofzero,youhavedonetheexactoppositeofwhatyouaretryingtoaccomplish.

DimintXasShort

intX=56000*998

DivisionoperatorTheregulardivision(/)andtheintegerdivision(\)operatorsdividetwonumbersand returnaresult.

Theusageis

RegularResult=Number1/Number2

IntegerResult=Number1\Number2Thedifferencebetweenthetwotypesofdivisionishowthenumbersontheright-hand sideoftheequalssignaretreatedbeforethedivisionoperationtakesplace.Ininteger division,integraldatatypesmustbeused.Thesearethedatatypesthatdonotallow decimalplaces,suchasInteger,Long,Bit,andShort.Theresultofaninteger divisionishowmanytimesonenumbercanevenlydivideintoanothernumber.

25\5=5

Thenumber5evenlydividesinto25fivetimes.

26\5<>5

Inthiscase,26dividedby5obviouslydoesnotequal5.Hereisthelongcaseexampleofseveralscenariosofchoosingthecorrectorincorrect typeofdivision:

DimintXAsInteger=100

DimintYAsInteger=50

MessageBox.Show(intX/intY)'Returns2

MessageBox.Show(intX\intY)'Returns2

intX=101'Modifyvariablesodivisionisnoteven

MessageBox.Show(intX/intY)'Returns2.02

MessageBox.Show(intX\intY)'Returns2

'Usefloatingpointvariables


DimdblYAsDouble=50

MessageBox.Show(dblX/dblY)'Returns2.0687

MessageBox.Show(dblX\dblY)'Returns2

ModulooperatorThemodulooperator(%)dividestwonumbersandreturnstheremainder. Theusageis

Result=Number1MODNumber2

Ifeitherofthenumbersbeingdividedarefloating-pointnumbers,theresultisthefloating-pointremainder.Ifthebothofthenumbersbeingdividedareintegers,thereturn valueisanintegerdatatype.

Hereisasummaryofsamplesusingthemodoperand: DimintXAsInteger=100

DimintYAsInteger=50

MessageBox.Show(intYModintX)'Returns50

MessageBox.Show(intXModintY)'Returns0

intX=101'Modifyvariablesodivisionisnoteven

MessageBox.Show(intXModintY)'Returns1

'Usefloatingpointvariables


DimdblYAsDouble=50.74

MessageBox.Show(dblXModdblY)'Returns1.955

MessageBox.Show(dblYModdblX)'Returns50.74

Asyoucansee,onceagain,usingthecorrectdatatypesandunderstandinghowyour divisionshouldtakeplacealterstheoutcomeofyourresults.

ExponentiationoperatorTheexponentiationoperator(^)returnstheexponentoftwonumbers. Theusageis

Result=Number1^Number2

Thefirstnumberisraisedtothepowerofthesecondnumber.Normallythedatatypeof theresultisdouble,unlessyouexplicitlydefinetheresultasanintegraldatatype.Here areafewsamplesoftheexponentialoperand:

DimintXAsInteger=50

DmintYAsInteger=5

DimintZAsInteger

Console.WriteLine(intYîntX)'Returns8.88178419700125E34

Console.WriteLine(intXîntY)'Returns312500000 intZ=intYîntX

Console.WriteLine(intZ)

'Overflowexceptionoccurs

'Theexponentofthe2floatingpoint

'numberscannotfitintoanintegerdatatype

DimdblXAsDouble=3

DimdblYAsDouble=3

Console.WriteLine(dblX ^dblY)'Returns27Intheprecedingexamples,Ithrewinanexampleofanexception,soyoucanseethat whendealingwithraisingnumberstothepowerofanothernumber,thereturndatatype shouldbeDouble,becausethenumbershaveatendencytobequitelarge.

Concatenationoperators

Concatenationoperators(&)combinestringvariableswithstringexpressions. Theusageis

Variable=expression&expression

DimXasInteger=3

DimintYasInteger=15

intX=intX&intY'Returns315

Or,youdonothavetoassignthevalueimmediately: Dimstr1asstring="NCC"

Dimstr2asstring="D"

str1=str1&"1701"&str2'ReturnsNCC1701DWhenyoucombinestringsinVisualBasic,youcanusethevariableontheleft-handside oftheequalssignasastringvariableintheexpressionontheright-handsideofthe equalssign.Sothestr1variableintheprecedingexamplecanbeusedinyour expressionaswellasintheresult.

Theadditionoperator(+)canalsobeusedforconcatenation,ifanyofthevaluesinthe expressionontheright-handsideoftheequalssignarestringdatatypes.Theprevious sectionsonarithmeticoperatorsshowedseveralexamplesofthisbehavior.

Assignmentoperators

Assignmentoperatorsarealmostascommonasarithmeticoperators.Theequals(=) signisusedwheneveryouneedtosetthevalueofavariable.Whenyoudeclare variables,youcanuseassignmenttosetthevalueofthevariableinthesamelinethat youaredeclaringit.

DimXasInteger=3

Table5-10:AssignmentOperators

Operator Action

= Equalsassignment

+= Addition/concatenation assignment

-= Subtraction assignment

*= Multiplication assignment

/=and\= Divisionassignment

=̂ Exponentiation assignment

&= StringConcatenation assignment

EqualsoperatorTheequalsoperator(=)isprobablythemostwidelyusedoperatorinanydevelopment language.Youarealwaysassigningavariableorobjecttotheresultofarithmetic,ora functioncallreturnvalue,oranyvaluethatyouneedtoassign.The=operatorisalso usedtocompareoneexpressionofvariabletoanother,returningaBooleanvalue.

Theusageis

Variable=Expression

Theexpressionontheright-handsideofthe=isevaluated,andassignedtothevariable ontheleft-handsideoftheoperator.

DimstrFirstNameasString="BillionDollar"

DimstrLastNameasString="Bill"

DimstrFullNameasstring

strFullName=strFirstName&strLastName'ReturnsBillionDollarBillIntheprecedingexample,youaretakingtwostringvariablesandassigningthemtothe variablestrFullName.

DimlngResultasLong lngResult=DoTheMath()

Inthisexample,thereturnvaluefromtheDoTheMathfunctionisassignedtothe variablelngResult.

Inalloftheexamplessofar,youhavebeenevaluatinganexpressionontheright-hand sideoftheoperatorandassigningavaluetotheleft-handside.Youcanalsocompare variableswiththeassignmentoperator:

IfbNotEmpty=TrueThen

Messagebox.Show("Please fillinavalueforname") Endif

IfstrName="SMITH"then

Messagebox.show("YournameisnotGates") EndifInthefirstexample,iftheBooleanvariablebNotEmptyhasavalueofTrue,thenyounotifytheuserthattheymustfillinavalueintoatextboxorwhatevercontrolyoumight beusing.Inthesecondexample,youcheckthevalueofthestrNamevariable,andifit equalsSMITH,youraiseamessagetotheuser.Bothoftheseexamplesusethe= operatortocheckforthevalueofanoperator,andnotnecessarilyassignavaluetoan operator.

Addition/concatenationassignmentoperatorTheaddition/concatenationassignmentoperator(+=)addsthevalueofanexpressionto thevalueofavariableandassignstheresulttothatsamevariable.Thetypeofoperation thatoccursisbasedonthetypeofdatathatisbeingevaluated.

Theusageis

Variable+=Expression

Iftheexpressionisnumeric,thenadditionoccurs;iftheexpressionisastring,then concatenationoccurs.

DimstrFNameasstring="Romeo"

DimstrLNameasstring="MustDie"HereyouhavethestrFNamevariablethatholdsavalueof"Romeo".Youthenusethat samevariableastherecipientoftheexpression+=strLName.Thisevaluationtakes thecontentsofstrFName,andconcatenatesstrLNametoit.Seethe"&="operatorlaterinthissectiontoaccomplishthesamethinginacleanerfashion.Youshouldalwaysavoidusingtheaddition(+)operatorforstringconcatenation.

strFName+=strLName'ReturnsRomeoMustDie

DimintXasInteger=100

intX+=1'Returns101HereyouareincrementingthevalueofintX.TheoriginalvalueofintXwas100,and usingtheassignmentconcatenationoperator,youcanincrementthevalueandassignit backtointX.Youcanaccomplishthesamethingwiththislineofcode:

intX=intX+1

DoWhileintX<100

intX+=1'Incrementintegervalueby1

Loop

MessageBox.Show(intX)'Displays100Whendiscussingtheadditionoperatorinthebeginningofthesection,yousawsomeof theerrorsthatcouldariseifyouareattemptingadditionandthedatatypeisnotnumeric.

DimVal1asInteger=100

DimVal2asInteger=50

Val1+=Val2' Returns150

DimVal1asString=100

DimVal2asstring=50

Val1+=Val2'Returns10050

Hereyoucanseethatbasedonthedatatype,eitheradditionorconcatenationmay occur.Youhaveobviouslydeclaredyourownvariableshere,butasImentionedbefore, youmightnotalwaysknowthedatatypeofthevariablesyouaredealingwith,souse cautionandmakesureyoucandeterminetheactualdatatypesbeforeperformingany operationsthatincludearithmetic.

SubtractionassignmentoperatorThesubtractionassignmentoperator(–=)subtractsthevalueofanexpressionfromthe valueofavariableandassignstheresulttothatsamevariable.

Theusageis

Variable-=Expression

Thesamerulesapplyforthesubtractionassignmentoperatorasforthesubtraction arithmeticoperator.

DimintXasinteger=100 intX-=25'Returns75

or

intX-=100+34'Returns-34Bothstatementsarefairlystraightforward.ThevariableintXisinitializedwithavalueof100,andtheexpressionontheright-handsideoftheoperandisevaluated,subtracted fromthevariableontheleft,andthenassignedtothevariableontheleft.

MultiplicationassignmentoperatorThemultiplicationassignmentoperator(*=)multipliesthevalueofanexpressionbythe

valueofavariableandassignstheresulttothatsamevariable.

Theusageis

Variable*=Expression

Thesamerulesapplyforthemultiplicationassignmentoperatorasforthemultiplication arithmeticoperator.

DimintXasinteger=3 intX*=3'Returns9

intX*=15'Returns45

DimintYasInteger=7

intX*=intY'Returns21

Youaredoingsimplemultiplicationhere,takingthevalueontheright,multiplyingitby thevariableontheleft,andassigningtheresulttothevariableontheleft.

DimintXasinteger=10IntX*=DoTheMath()Inthisexample,youareevaluatingtheexpressionDoTheMath,afunctioncall, multiplyingitbyintX,andassigningtointX.IfthefunctionDoTheMathreturned10, yourresultwouldbe100;ifitreturned3,yourresultwouldbe30,or3*10.

DimintXasinteger=27000 intX*=129093482^45

Division assignmentoperatorThefloating-pointdivision(/=)andintegerdivision(\=)assignmentoperatorsdividethe valueofanexpressionbythevalueofavariableandassigntheresulttothatsame variable.

Theusageis

FloatingPointVariable/=Expression integralVariabe\

=Expression

Thesamerulesthatyoulearnedearlierinthechapterregardingfloating-pointand integraldivisionapply.Here isasummaryofexamplesusingthedivisionassignment operators:

DimintXasinteger=5

DimintYasinteger=25 intY/=intX 'Returns5

DimdblXasDouble=234.6

DimdblYasDouble=23.928

dblX/=dblY'Returns9.80441323971916

DimintXasInteger=200

DimdblYasDouble=5.34 intX\=dblY'Returns40

ExponentiationassignmentoperatorTheexponentiationoperator(^=)raisesthevalueofavariabletothepowerofan expressionandassignsittothatvariable.

Theusageis

Variable^=Expression

Thevariableontheleft-handsideoftheoperatorisraisedtothepoweroftheexpression ontheright-handsideoftheoperator.

DimintXasInteger=3

DimintYasInteger=5 intX^=intY'Returns243

DimintX=10

DimintY=3

IntX^=intY'Returns1000Thisexampleisthesameas10*10*10.Ifyouweretomakethatsomewhatgeneric, youcouldcodelikethis:

DimintVar1asInteger

ForintVar1=0tointY—1 intX=intX*intX

Next

Obviouslyusingthecorrectoperatorsimplifiesyourcode,anddoesnotleaveroomfor anyerrors.

ConcatenationassignmentoperatorTheconcatenationoperator(&=)concatenatesastringexpressiontoastringvariable andassignsittothestringvariable.

Theusageis

Variable&=Expression

Thevariableontheleft-handsideoftheoperatorisconcatenatedtotheexpressionon theright-handsideoftheoperator.

DimstrNameasstring="Dr." DimstrVarasstring="Evil"

strName&=strVar'ReturnsDr.Evil

DimintXasInteger=3

DimintYasinteger=5 intX&=intY'Returns35

Theinclusionoftheintegerexampleintheprecedingcodeistodemonstratethatthe&= operatoralwaystreatsthevariablesandexpressionsasstrings,sonoadditionoccursas withthe+=operatorifthevariableandexpressionareactualnumbers.

Comparisonoperators

Comparisonoperatorsevaluateanexpressionontheright-handsideoftheequalssign andreturnaBooleanTrueorFalsebasedonthecomparisonoftheexpressions.

Theusageis

result=expression1comparisonoperatorexpression2 result=object1Isobject2

result=stringLikepattern

DimintXAsInteger=3

DimintYAsInteger=5

Console.WriteLine(intX<intY)

ThisexamplereturnsTrue,becausetheintegervalue3islessthantheintegervalue5. DimintXAsString="A"

DimintYAsString="a" Console.WriteLine(intX>intY)'ReturnsFalse

Console.WriteLine(Asc("A")) 'Returns65

Console.WriteLine(Asc("a")) 'Returns97

Thiscomparisonisbasedonstrings,whichisalittledifferentthannumericcomparison. Youhavecompared"A"and"a",whichthecompilerconvertstotheirrespectiveASCII equivalenttodothecomparisonbasedonthesortorderoftheASCIIvalue.TheASCII valuefor"A"is65,andtheASCIIvaluefor"a"is97,whichiswhyFalseisreturned fromthecomparison;65isnotgreaterthan97.Whencomparisonoperatorsareused withstrings,theASCIIequivalentofthestringvaluesiscomparedtoevaluatethe expressions.Table5 - 1 1 liststhecomparisonoperatorsandtheactionstheyperform.Table5-11:ComparisonOperators

Operator Action

Is Object compari son

Like String pattern compari son

< Less than

<= Less thanor equalto

> Greater than

>= Greater thanor equalto

= Equalto

IsoperatorTheIsoperatorcomparestwoobjecttypesandtestswhethertheyarethesame, alwaysreturningaBooleanvalue.

Theusageis

Result =objectXIsobjectYTheonlywaytogetaTruevaluebackfromthecomparisonisiftheobjectsrefertothe sameobject.Iftherearetwoobjectsthatareofthesametypebutdonotreferbackto thesameobject,thatis,theobjectwasnotcreatedfromthatobject,theresultisalways False.HereisasummaryofexamplesusingtheIsoperator:

DimxAsSystem.String DimyAsNewObject()

DimvAsObject

v=y

Console.Write(vIsy)'ReturnsTrue

Console.Write(xIsy)'ReturnsFalse

LikeoperatorTheLikeoperatorreturnsaBooleanvaluebasedontheevaluationofastringanda pattern.Ifthepatternmatchesthestring,Trueisreturned;otherwiseFalseisreturned.

Theusageis

Table5-13:ComparisonOperators

Operator Usage True Exam ple

False Exam ple

< Expr1< Expr2

27<45

45<27

<= Expr1<= Expr2

45<=45

16<=6

> Expr1> Expr2

98>97

98>98

>= Expr1>= Expr2

98>=98

97>=98

= Expr1= Expr2

98=98

98=100

<> Expr1<>Exp2

98<>97

98<>98

Result=StringLikePatternTheresultscanalsovarybasedontheOptionComparestatement.IfOption Compareis settoTEXT,thenacaseinsensitive,textsortisusedtodeterminetheresult. If OptionCompareBINARY(default)isset,thepatternmatchingisbasedonthebinaryrepresentationofthecharacters,basedonlocale,andnotthetextual representationofthecharacters.Table5 - 1 2 liststhepatternmatchingsyntaxforcharacter,numeric,andwildcard charactermatching.Table5-12:PatternMatchingSyntax

Character Meaning? Matches anysingle character.

* Matches zeroor more characters.

# Matches anysingle digit(0–9).[…] Character list surrounde dby brackets canmatch any character inthelist. For

example:[bilgates].

[!…] Character list surroundedby bracketsprefixedby exclamationpoint matchany single character notinthe list.

X—X Characters separated bya hyphen specifya rangeof Unicode characters

Console.Writeline("DOG" Like"D*")'ReturnsTrue

Console.Writeline("a"LIKE"A")'ReturnsFalse

Console.Writeline("XYZ"LIKE"X[ACY]?")ReturnsTrue

Theprecedingexamplesgiveasummaryofthepatternmatchingsyntax.

ComparingstringsandnumbersTheremainingcomparisonoperatorsarecoveredasagroupratherthanoneatatime becausetheyallfollowthesamerules,andtheyallactexactlyasyouwouldexpect.The onlythingthatyouneedtoworryaboutisthedatatypethatyouarecomparing:stringsornumbers.Eitherway,youarereturningaBooleanvalue.Table 5 - 1 3 liststheremainingnumericcomparisonoperatorsandthepossiblevaluestheevaluated expressionscanreturn.

Logical/bitwiseoperators

TheoperatorsusedforeitherthelogicalevaluationoftheBooleanexpressionsorbitwise

evaluationofthenumericexpressionsarecalledlogical/bitwiseoperators.Thesyntaxfor usingthelogical/bitwiseoperatoris

Var_result=Expr1OperatorExpr2

where Var_resultisanyBooleanornumericvariable. Expr1andExpr2areBooleanornumericexpressions. Operatorisanylogical/bitwiseoperator,suchasAnd,Or,Not,orXOR.

Table5-14:LogicalOperation

Operation Description

And Usedto perform logical joiningon twoBooleanexpressions.Itreturns Trueifboth theBoolean expressions areTrue.

Or Usedto perform logical disjoiningon twoBoolean expressions. Itreturns Trueifanyof theBoolean expressions isTrue.

Not Usedto perform logical negationon aBooleanexpressions. Itreturns Falseifthe Boolean expressionisTrueandvice-versa.

Xor Usedto perform logical exclusionon twoBoolean expressions. Itreturns Trueonlyif oneofthe Boolean expressionisTrue.

AndAlso Usedto perform logical joiningoftwoBooleanexpressions inashort-circuit manner.It returnsTrue ifboththe expressions areTrue. However,if thefirst expression

Tounderstandthelogicaloperationoftheseoperators,considerthefollowingexample:

'DeclarethreeIntegervariables

DimintVar1AsInteger=16



'DeclareaBooleanvariable

DimbResultAsBoolean

'UseAndOperator

bResult=intVar1>intVar2AndintVar2>intVar3 'ReturnsTrue

bResult=intVar1>intVar2AndintVar3>intVar2 'ReturnsFalse

'UseOrOperatorbResult=intVar1>intVar2OrintVar2>intVar3 'ReturnsTrue

bResult=intVar1>intVar2OrintVar3>intVar2 'ReturnsTrue

bResult=intVar2>intVar1OrintVar3>intVar2 'ReturnsFalse

'UseNotOperator

bResult=Not(intVar1>intVar2) 'ReturnsFalse

bResult=Not(intVar1<intVar2) 'ReturnsTrue

'UseXorOperator

bResult=intVar1>intVar2XorintVar2>intVar3 'ReturnsFalse

bResult=intVar1>intVar2XorintVar3>intVar2 'ReturnsTrue

bResult=intVar2>intVar1XorintVar3>intVar2 'ReturnsFalse

'UseAndAlsoOperator

bResult=intVar1>intVar2AndAlsointVar2>intVar3

'ReturnsTrue

bResult=intVar2>intVar1AndAlsointVar2>intVar3

'ReturnsFalse—SecondConditionisnotevaluated

'UseOrElseOperator

bResult=intVar1>intVar2OrElseintVar2>intVar3

'ReturnsTrue

bResult=intVar1>intVar2OrElseintVar3>intVar2

'ReturnsTrue—SecondConditionisnotevaluated

Operatorprecedence

Inalloftheexamples,youhaveseenfairlysimpleexpressions.Thisisnotalwaysthe casewhenyouarewritingyourapplications,andyoumayhaveseveraldifferent operatorsbeingusedtoevaluateasingleexpressionorseriesofexpressions.

DimdblRetasInteger

dblRet=5*4/6^4+9—100

Console.Writeline(dblRet) 'Returns-90.9845679012346Inthisstatement,fiveoperatorsarebeingusedtoretrievethevalueofintRet.The precedenceinwhichtheoperatorsareevaluatedaffectstheoutcome.

DimdblRetAsDouble

dblRet=((5*4)/6)^4+9-100

Console.WriteLine(dblRet) 'Returns32.4567901234568Youcanseethedifferenceinthetwoexamples.Althoughtheybothareusingthesame numbers,theresultsaredifferentbasedontheusageofparenthesesonthecode.So twothingsareactuallyaffectingtheoutcome:

1. Thelocationoftheparenthesesintheexpression.2. Theorderoftheoperatorsintheexpression.

Table5 -1 6liststheprecedenceofoperatorswhenevaluatingexpressions.Table5-16:OperatorPrecedence

Arithmetic Comparison Logical

^ = Not

-(Negation) <> And

*,/ < Or

\ > XOR

Mod <=

+,- >=

BitwiseOperators Like,Is, TypeOf..Is

&

Whenparenthesesareusedinexpressions,theyarealwaysevaluatedfirst.Sointhe previousexample,therearetwodifferentresultsforthesamenumbersbecausethe parentheseshaveoverriddentheprecedenceoftheoperators,causingaportionor portionsoftheexpressiontobeevaluatedbyothers.

Hereisasummaryoftherules: Operatorevaluationbeginsfromthelefttotheright.

Arithmeticoperatorsarealwaysevaluatedfirst,thencomparison operators,followedbylogicaloperators.

Comparisonoperatorsallhaveequalprecedence. Operationsenclosedwithparenthesesareevaluatedbeforeexpressions outsideoftheparentheses. Concatenation(&)operatorprecedesallcomparisonoperatorsand

followsmathematicaloperators.

Theserulesareveryeasytounderstand;theyfollowthelogicalorderinwhichyouwould processtheseexpressionsonpaperorusingacalculator.Youalwaysfigureoutyour grouping,processthoseinstructionsandthenmoveontothemath,andfinallyyou comparetheresultsoftheexpressionsandcomeupwiththeanswer.

Chapter6:ArraysIn This Chapter

IntroducingarraysMultidimensionalarraysDynamicarraysTheArrayClassmembersArraysofarrays

Arrayshelpyoustoredatainacontiguousmemoryarea..

Introducing ArraysAnarrayisamemorylocationthatisusedtostore multiplevalues.Allthevaluesinanarrayareofsametype,suchasIntegerorStringandarereferencedbytheirindexorsubscriptnumber,whichistheorderinwhichthesevalues arestoredinthearray.Thesevaluesarecalledtheelementsofanarray.Thenumberof elementsthatanarraycontainsiscalledthelengthofthearray.InVB.NET,allthearraysareinheritedfromtheSystem.Arrayclass.TheArrayclassisamemberoftheSystemnamespace.TheArrayclassprovidesmethodsforcreating,searching,sorting, andmodifyingarrays.SomeofthecommonlyusedmethodsoftheArrayclassare GetUpperBound,GetLowerBound,andGetLength.Arrayscanbesingle-ormultidimensional.

DimArray_Name(Num_Elements)[AsElement_Type]

whereArray_Namereferstothenameofthearray.Num_Elementsreferstothenumberofelementsthearraycancontain.

Element_Typereferstothedatatypeofelements.Thisparameteris optional.IfyoudonotspecifytheElement_Type,thearrayisoftype Object.

Forexample,

DimEmp_Name(100)asStringThisstatementdeclaresanarraynamedEmp_NameoftypeString,anditcanstore101valuesoftypeString.Thisisbecausethestartingindexofanarrayiszero.

Youcanalsorewritetheprecedingstatementasfollows:

DimEmp_Name()AsString=NewString(100){}

Afterdeclaringanarray,youneedtoassignvaluestoit.Considerthefollowingexample, whichillustratesassigningvaluestoanarray:

Emp_Name(0)="Jack" Emp_Name(1)="Peter"

Emp_Name(2)="John"

…

…

Emp_Name(100)="Michelle"Inthisexample,Jackisstoredattheindex0ofthearrayEmp_Name.Similarly,Peter,

John,andMichellearestoredatindices1,2,and100,respectively.Thisimpliesthatthe arraycanstore101elements.Here,0isthestartingindexorthelowerboundofthe array.Thelowerboundisfixedforallthearrays.Here,100istheupperboundofthe arrayanditcandifferfromarraytoarraydependingonthesizespecified.

Thelowerboundofanarrayisalwayszero.Theupperboundofanarrayisoneless thanthenumberofelementsinthearray.

Multidimensional ArraysDimarr(10,2)asStringTheprecedingstatementdeclaresatwo-dimensionalarray,arr,oftypeString.Atwo- dimensionalarrayhastwoindices,whichhelpsyoutospecifythepositionofelementsin thearray.

Dimarr1(10,10,10)asIntegerTheprecedingstatementdeclaresathree-dimensionalarray,arr1,oftypeInteger. Thenumberofdimensionsinanarrayiscalledtherankofanarray.Sothearray mentionedintheprecedingstatementhasarankof3.Eachdimensioninanarraycan haveadifferentlength.

Considerthefollowingexample,whichdescribestheprocessofcreatingatwo- dimensionalarrayandstoringthedatainit.

DimEmp_Details(10,6)AsStringTheprecedingstatementcreatesanarray,Emp_Details,oftypeString.Now, considerthefollowingstatementstoinitializevaluesinthisarray:Emp_Details(0,0)="John"TheprecedingstatementstoresthevalueJohnattheindexposition(0,0).

Emp_Details(0,1)="$10000"Theprecedingstatementstoresthevalue$10000attheindexposition(0,1).

MessageBox.Show(Emp_Details(0,1))Theprecedingstatementdisplaysthevaluestoredattheindexposition(0,1)ofthe arrayEmp_Details.

Dynamic ArraysYoucreateadynamicarraybynotspecifyingthesizeofthearrayatthetimeofthearray declaration.Tounderstanditbetter,considerthefollowingexample:

DimCand_Name()asStringIntheprecedingexample,Cand_NameisadynamicarrayoftypeString.Notethatthe numberofelementsinthearrayisnotspecified.YouusetheReDimstatementtospecify thesizeofthisarray.

TheReDimstatementYouusetheReDimstatementtospecifyorchangethesizeofoneormoredimensionsofanarraythathasalreadybeendeclared.However,theReDimstatementcannotchangethenumberofdimensionsinanarray.WhentheReDimstatementisexecuted,theexistingcontentsofthearrayarelost.ThisisbecausetheReDimstatementreleasesthearrayresourcesandcreatesanewarray.SomeofthefeaturesoftheReDimstatementare

TheReDimstatementdoesnotchangethedatatypeofthearrayor initializenewvaluesforthearrayelements.Theelementsofthenew arrayareinitializedwiththedefaultvaluesoftheirdatatype.

TheReDimstatementcanbeusedattheprocedurelevelonlyandnotattheclassormodulelevel.

ThefollowingstatementillustratestheuseoftheReDimstatement: DimCand_Name()asString

ReDimCand_Name(10)Intheprecedingexample,Cand_NameisadynamicarrayoftypeString.TheReDim statementresizesthearrayCand_Nameto10.Youcannowstore11stringsinthe array.TheReDimstatementcanalsobeusedforresizingmultidimensionalarrays.However,youcannotchangethenumberofdimensionsinanarray.Tounderstandthisbetter, considerthefollowingexample:

'Declaresamultidimensionalarray

DimArry(10,20)AsString

'Resizingthearray

ReDimArry(15,25)

Intheprecedingexample,Arryisamultidimensionalarray.Thesizeofthefirst dimensionischangedfrom10to15andtheseconddimensionischangedfrom20to25 byusingtheReDimstatement.

The Array Class MembersTheArrayclassprovidesvariousmethodsthathelpyouinmanipulatingthearrays. Someofthecommonlyusedfunctionsarementionedinthefollowingsections.

TheGetUpperBoundfunctionTheGetUpperBoundfunctionreturnstheupperboundofthespecifieddimensionofan array.Ittakesthedimensionforwhichtheupperboundistobefoundasaparameter. Thesyntaxis

Array_name.GetUpperBound(Dimension)

Intheprecedingsyntax Array_namereferstothenameofthearrayforwhichtheupperbound istobefound. Dimensionreferstothedimensionnumberforwhichtheupperboundis

tobefound.Youuse0forthefirstdimension,1forthesecond dimension,andsoon.Considerthefollowingexample,whichusestheGetUpperBoundfunction:

Dimvar1(10,20,30)asStringDimResultasInteger

Result=var1.GetUpperBound(0) 'Returns10



TheGetLowerBoundfunctionYouusetheGetLowerBoundfunctiontofindthelowerboundofthespecified dimensionofanarray.However,becausethelowerboundofanarrayisalways0,this functionwillalwaysreturn0.Italsotakesthedimensionforwhichthelowerboundisto befoundasaparameter.Thesyntaxis

Array_name.GetLowerBound(Dimension)

Intheprecedingsyntax Array_namereferstothenameofthearrayforwhichthelowerboundis tobefound. Dimensionreferstothedimensionnumberforwhichthelowerboundis

tobefound.Youuse0forthefirstdimension,1fortheseconddimension,andsoon.

TheGetLengthfunctionYouusetheGetLengthfunctiontofindthenumberofelementsinthespecified dimensionofanarray.Thesyntaxis

Array_name.GetLength(Dimension)

Intheprecedingsyntax Array_namereferstothenameofthearraywhoselengthistobe found. Dimensionreferstothedimensionnumberforwhichthelengthistobe

found.Youuse0forthefirstdimension,1fortheseconddimension,and soon.

TheSetValuefunctionYouusetheSetValuefunctiontosetavalueforaspecificarrayelement.Youcanuse thisfunctiontosetvaluesinsingle-ormultidimensionalarrays.ThesyntaxoftheSetValuefunctionforstoringvaluesinasingle-dimensionalarrayis

Array_name.SetValue(Value, Pos)Intheprecedingsyntax:

Array_namereferstothenameofasingle-dimensionalarrayforwhich thevalueoftheelementistobeset. Valueisthevaluetobestoredorsetatthespecifiedposition. Posistheindexnumberatwhichthevalueistobestored.

ThesyntaxoftheSetValuefunctionforstoringvaluesinatwo-dimensionalarrayis

Array_name.SetValue(Value, Pos1,Pos2)

Intheprecedingsyntax: Array_namereferstothenameofatwo-dimensionalarrayforwhichthe valueoftheelementistobeset. Valueisthevaluetobestoredorsetatthespecifiedposition.

Pos1andPos2aretheindexnumbersspecifyingtherowandthe columnatwhichthevalueistobestored.

ThesyntaxoftheSetValuefunctionforstoringvaluesinathree-dimensionalarrayis

Array_name.SetValue(Value, Pos1,Pos2,Pos3)

Intheprecedingsyntax: Array_namereferstothenameofathree-dimensionalarrayforwhich thevalueoftheelementistobeset. Valueisthevaluetobestoredorsetatthespecifiedposition. Pos1,Pos2,andPos3arethefirst-,second-,andthird-dimensionindex numbersofthearray.

ThesyntaxoftheSetValuefunctionforstoringvaluesinamultidimensionalarrayis

Array_name.SetValue(Value, Pos())

Intheprecedingsyntax: Array_namereferstothenameofamultidimensionalarrayforwhich thevalueoftheelementistobeset. Valueisthevaluetobestoredorsetatthespecifiedposition. Pos()isaone-dimensionalarraythatcontainstheindexnumbersat whichthevaluesaretobestored.

Arrays of ArraysVB.NETallowsyoutocreateanarraycontainingsub-arrays.

Forexample,

'Declarethebasearray

DimmyArray()()AsInteger=NewInteger(2)(){}

'Assignfirstsubarrayattheindexposition0 myArray(0)=NewInteger(5)

{1,3,5,7,9,10}

'Assignsecondsubarrayattheindexposition1 myArray(1)=NewInteger(4)

{2,4,6,8,20}Inthisexample,myArrayisanIntegerarray.ThisarraycontainstwoIntegersub- arrays.

Considerthefollowingstatement,whichexplainshowtoaccesstheelementsofthese arrays:

MessageBox.Show(myArray(1)(4))

Chapter7:ConditionalLogicIn This Chapter

If…Then…ElseSelect…CaseDo…LoopWhile…EndWhileFor…NextForEach…Next

VB.NEThasstatements,suchasIf…Then…ElseandSelect…Case,whichhelpyoutoconditionallyexecuteyourprogram.VB.NETalsoprovidesyouwithvariouslooping statements,suchasDo…Loop,While…EndWhile,andFor…Next,whichhelpyour programtorepeatasetofstatements,conditionally.Inthischapter,youlearnaboutthe syntaxandimplementationofthesestatements.

The If…Then…Else StatementThesyntaxofthesingle-lineIf…Then…Elsestatementis

If conditionThenstatement[Elsestatement]Intheprecedingsyntax,condition,whichisaBooleanexpression,isevaluated.Ifthe conditionistrue,thestatementfollowingThenisexecuted.Iftheconditionisfalse,the statementfollowingElseisexecuted.However,theElsepartisoptional.

Thefollowingexampleillustratestheuseofsingle-lineIf…Then…Elsestatement:

IfQtyOrdered>10ThenDiscount=20ElseDiscount=10

Inthisexample,thevalueofthevariableQtyOrderedisevaluated.Ifitisgreaterthan10,thevalueofDiscountissetto20;otherwise,itissetto10.

Youcanhavemultiplestatementsinthesingle-lineformoftheIf…Then…Else statement.However,allthestatementsneedtobeonthesamelineandshouldbe separatedbyacolon.Thesyntaxis

If conditionThenstatement:[statement]:[statement]Thefollowingexampleillustratestheuseofmultiplestatementsinasingle-lineIf…Then…Elsestatement:

IfQtyOrdered>10ThenDiscount=20:MsgBox("Discountis"

&iDiscount)

Inthisexample,thevalueofthevariableQtyOrderedisevaluated.Ifitisgreaterthan10,thevalueofDiscountissetto20andamessageboxisdisplayed.However, multiplestatementsinasinglelinemightaffectthereadabilityofthecode.Insucha situation,youcanbreakasingle-lineIf…Then…Elsestatementtomultiplelines.The syntaxforamultiple-lineIf…Then…Elsestatementisasfollows:

If conditionThen statement(s)

[Else

[statement(s)]] EndIfInamultiple-lineIf…Then…Elsestatement,theEndIfstatementisusedtomarkthe endofanIf…Then…Elsestatement.

Thefollowingexampleillustratesthepoint: IfQtyOrdered>10Then

Discount=20

Else

Discount=10

EndIf

The Select…Case StatementYouusetheSelect…Casestatementtoexecutedifferentsetsofstatementsbasedon thevalueofanexpression.TheSelect…Casestatementissimilartothe If…Then…Elsestatement.TheonlydifferencebetweenthetwoisthatIfandElseIf canevaluatedifferentexpressionsineachstatement,whereastheSelectstatement canevaluateonlyoneexpression.TheSelectstatementthenusestheresultofthis expressiontoexecutedifferentsetsofstatements.However,theSelect…Case statementispreferredoverIfandElseIfstatementwhenyouneedtousemultiple conditionsbecauseitmakesthecodeeasytoreadandunderstand.Thesyntaxforthe Select…Casestatementis

SelectCaseexpression

Caseexpressionlist statement(s)

[CaseElse

[statement(s)]] EndSelectIntheprecedingsyntax,expressionlistreferstotheconstantsorexpressionsthatarecomparedwiththeresultoftheexpressionmentionedwiththeSelect…Casestatement.WhentheSelect…Casestatementisexecuted,theexpressionisevaluatedandtheresultiscomparedwitheachconstantspecifiedwiththe Casestatement.IftheresultoftheexpressionisequaltoanyoftheCaseconstants, statementsfollowingthatCasestatementareexecuted.However,ifnomatchisfound fortheexpressionresult,statementsfollowingtheCaseElsestatement(ifitispresent) areexecuted.TheEndSelectstatementmarkstheendoftheSelect…Case statement.

Forexample:

SelectCaseMonth

Case1

Msgbox("January") Case2

MsgBox("February")

…

…

Case12MsgBox("December") CaseElse

MsgBox("Incorrectnumber")

EndSelect

Do…Loop StatementTheDo…Loopstatementsareusedtoexecuteasetofstatementsrepeatedly.ThesyntaxoftheDo…Loopstatementis

DoWhile|Untilcondition

[statements] [ExitDo] [statements]

Loop

or

Do [statements] [ExitDo] [statements]

LoopWhile|Untilcondition

IntheprecedingsyntaxWhile|Untilarethekeywordsthatareusedtorepeattheloop.Youcan

useonlyoneofthematatime.UseWhiletorepeattheloopuntilthe conditionbecomesfalseanduseUntiltorepeattheloopuntilthe conditionbecomestrue.

TheExitDostatementisusedtoexittheDoloop.Asaresult,thestatementfollowingtheLoopstatementisexecuted.IfyouplacetheWhileorUntilaftertheLoopstatement,theloopwillbeexecutedatleastonce. Forexample:

DimCtrasInteger=1

DoWhileCtr<=10

MsgBox("Thevalueofcounteris"&Ctr) Ctr=Ctr+1

LoopInthisexample,thesetofstatementswithintheDo…Loopstatementisrepeated10 times.

While…End While StatementYouusetheWhile…EndWhilestatementstorepeatasetofstatementsaslongasthe conditionistrue.ThesyntaxfortheWhile…EndWhilestatementis

Whilecondition

statements

EndWhileIntheprecedingsyntax,iftheconditionistrue,thestatementsareexecuted.TheEndWhilestatementmarkstheendoftheWhilestatement.

Forexample:

DimCtrasInteger=1

WhileCtr<=10

MsgBox("Thevalueofcounteris"&Ctr) Ctr=Ctr+1

EndWhileInthisexample,thesetofstatementswithinWhile…EndWhilestatementisrepeated10times.

For…Next StatementTheFor…Nextstatementsareusedtorepeatasetofstatementsaspecifiednumberof times.ThesyntaxfortheFor…Nextstatementis

ForCounter=<StartValue>To<EndValue>[StepValue] [Statement(s)]

[ExitFor]Next[Counter]

IntheprecedingsyntaxCounterisanynumericvariable.StartValueistheinitialvalueofthecounter.EndValueisthefinalvalueof thecounter.StepValueisthevaluebywhichthecounterisincremented.Itcanbe

positiveornegativeandisoptional.Ifyouomitthestepvalue,thedefaultis setto1.Statementsreferstothecodethatisexecutedthegivennumberoftimes.

TheExitForstatementisusedtoexittheForloop.Asaresult,the statementfollowingtheNextstatementisexecuted.

TheNextstatementmarkstheendoftheForstatement.AssoonastheprogramencounterstheNextstatement,thestepvalueisaddedtothe counterandthenextiterationofthelooptakesplace.Itisgood programmingpracticetospecifythenameofthecounterintheNext statement.

For Each…Next StatementTheForEach…Nextstatementisusedtorepeatasetofstatementsforeachelement inanarrayorcollection.TheForEach…Nextstatementisexecutedifthereisatleast oneelementinanarrayorcollection.Thelooprepeatsforeachelement.Thesyntaxof theForEach…Nextstatementis

ForEachComponentInSet

[Statement(s)] [ExitFor]

Next[Counter]

IntheprecedingsyntaxComponentisthevariableusedtorefertotheelementsofanarrayora collection.Setreferstoanarrayoranobjectcollection.

Forexample:

DimArr()asString={"Mon","Tues","Wed","Thurs","Fri","Sat"}

DimArrelementasString

ForEachArrelementinArr

MsgBox(Arrelement) NextInthisexample,ArrisanarrayoftypeStringthatstoresweekdays.Arrelementisa string.Here,theForEach…Nextstatementisusedtodisplayalltheelementsofthe arrayArr.

Unit IIChapter 8 :ProceduresChapter 9 :DialogBoxesChapter10:FileIOandSystemObjectsChapter11:DictionaryObjectChapt er12 :ErrorHandlingChapter13:NamespacesChapter14:ClassesandObjects

Chapter15:MultithreadingChapter16:COMInteropandMSMQ

Chapter8:Procedures

In This ChapterIntroductiontoproceduresFunctionstatementSubstatementBuilt-infunctionsinVB.NET

Procedures OverviewProcedurescontainalloftheexecutablecodeinyourapplication.ProcedureaccessmodifiersAprocedureiscreatedwithinaclassoramodule.Youcanalwayscallaprocedurefrom thesameclassormoduleinwhichitiscreated.However,youcancalltheprocedure fromdifferentclassesandmodulesdependingontheaccessmodifierusedwhilecreatingtheprocedure.Theaccessmodifiersdeterminethescopewithinwhichaprocedurecanbecalled.ThefollowingliststhevalidaccessmodifiersforallSubandFunctionprocedures:

Public:Proceduresthatcancalledfromanyclassormoduleinthe application.

Private:Proceduresthatcanbecalledonlyfromtheclassormodule wheretheyaredeclared. Shared:Proceduresthatarenotassociatedwithaninstanceofaclass. Protected:Proceduresthatcanbecalledfromtheclassormodule

wheretheyaredeclaredorfromthederivedclasses. Friend:Proceduresthatcanbecalledfromanyclassormoduleinthe

applicationthatcontainsitsdeclaration. ProtectedFriend:ProceduresthathavebothProtectedandFriend access.

Advantagesofprocedures

Asmentionedearlier,proceduresallowlogicalgroupingofcodeintotasks.Whena complexapplicationisdividedintoprocedures,thecodeismoreflexibleandeasierto maintainanddebug.Creatingprocedurestoperformasingletaskhasthefollowing benefits:

Thecodeinaprocedureisreusable.Afteraprocedureiscreatedandtested,itcanbecalledfromdifferentplacesinanapplication.

Theapplicationiseasiertodebugandmaintain,becauseyoucaneasily tracethesourceof anerrorina procedureinsteadof checkingtheentire applicationforerrors.

Types of ProceduresThetwotypesofprocedurescoveredinthischapterareSubproceduresandFunctionprocedures.

Subproceduresperformspecifictasks,suchasgeneratinganOrderIDor connectingtoadatabase.However,theseproceduresdonotreturnavalue tothecallingstatement.

last:Functionproceduresperformspecifictasksandreturnavaluetothecallingstatement.

SubproceduresYoucancreateaSubprocedureinmodulesandclasses.Thedefaultaccessmodifierfor SubproceduresisPublic,indicatingthatSubprocedurescanbecalledfromanywhere inanapplication.ThisistheexactoppositeofpreviousversionsofVisualBasic,where thedefaultaccessmodifierwasPrivate.ThesyntaxforcreatingaSubprocedureis

[<attrlist>][{Overloads|Overrides|Overridable| NotOverridable|MustOverride|

Shadows|Shared}]

[{Public|Protected|Friend|ProtectedFriend|Private

}]

Subname[(arglist)] [statements]

[ExitSub]

[statements] EndSub

Intheprecedingsyntax Overloadsindicatesthatthereareotherproceduresintheclasswith

thesamename,butwithdifferentarguments. Overridesindicatesthattheprocedurecan"override"anidentically

namedprocedureinthebaseclass. Overridableindicatesthattheprocedurecanbeoverriddenbyan

identicallynamedprocedureinaderivedclass. NotOverridableindicatesthatthisprocedurecannotbeoverriddenin

aderivedclass. MustOverrideindicatesthattheprocedureisnotimplementedinthe

classandmustbeimplementedinaderivedclassfortheclasstobe creatable.

[Public|Protected|Friend|ProtectedFriend| Private]representstheaccessmodifierfortheSubprocedure.Ifyou donotspecifyanyaccessmodifier,Publicisusedbydefault.

SubindicatesthattheprocedureisaSubprocedure. <ProcedureName>representsthenameoftheprocedure. ([Argumentlist])representsthelistofargumentstobepassedto theprocedure. EndSubindicatestheendoftheSubprocedure.

PublicSubCalculateDiscount(dblQuantity AsDouble,_

dblPriceAsDouble)

DimdblAmountAsDouble

DimdblDiscountAsDouble

dblAmount=dblQuantity*dblPrice

IfdblAmount>=150AnddblAmount<250Then dblDiscount=0.1

ElseIfdblAmount>=250Then dblDiscount=0.15

EndIf

TheSubMainprocedureTheSubprocedurethatisexecutedfirstwhenaVisualBasicprogramisrunistheMainprocedure.Thesyntaxofthisprocedureis

SubMain()

'Codehere

EndSubTheSubMainprocedureisthestartingpointofeveryapplication.EveryVisualBasic.NETapplicationmustcontainaSubMainprocedure.Youcanincludeanyinitialization codethatyoumighthaveintheSubMainprocedure,suchasconnectiontoadatabase orauthenticatingauser.

FunctionproceduresLikeSubprocedures,Functionprocedures(orfunctions),performaspecifictaskand arecreatedinclassesandmodules.However,unlikeSubprocedures,Function procedurescanreturnavalue.BecauseFunctionproceduresreturnavalue,youneed todefinethedatatypeforthereturnvaluewhilecreatingaFunctionprocedure.The syntaxforcreatingaFunctionprocedureis

[<attrlist>][{Overloads|Overrides|Overridable| NotOverridable|MustOverride|

Shadows|Shared}]

[{Public|Protected|Friend|ProtectedFriend|Private

}]Functionname[(arglist)][Astype][statements]

[ExitFunction] [statements]

EndFunction

Intheprecedingsyntax Overloadsindicatesthatthereareotherproceduresintheclasswith

thesamename,butwithdifferentarguments. Overridesindicatesthattheprocedurecan"override"anidentically

namedprocedureinthebaseclass. Overridableindicatesthattheprocedurecanbeoverriddenbyan

identicallynamedprocedureinaderivedclass. NotOverridableindicatesthatthisprocedurecannotbeoverriddenin aderivedclass. MustOverrideindicatesthattheprocedureisnotimplementedinthe

classandmustbeimplementedinaderivedclassfortheclasstobe creatable.

[Public|Protected|Friend|ProtectedFriend| Private]representstheaccessmodifierfortheSubprocedure.Ifyou donotspecifyanyaccessmodifier,Publicisusedbydefault.

FunctionindicatesthattheprocedureisaFunctionprocedure. <FunctionName>representsthenameoftheFunctionprocedure. ([Argumentslist])representsthelistofargumentstobepassedto

theFunctionprocedure.Theargumentscanbepassedbyvalueorby reference. [As<type>]representsthedatatypeofthereturnvalueofthe

Functionprocedure. ExitFunctionexplicitlyexitsafunction.Therecanbemorethanone

ExitFunctionstatementinafunction. EndFunctionindicatestheendoftheFunctionprocedure.

Built-in FunctionsVisualBasichasmanybuilt-infunctionsthatareveryusefulineasingyourdevelopment.

Inthissection,youlearnaboutthefunctionsandpropertiesinthefollowingnamespaces:Microsoft.VisualBasic.ConversionMicrosoft.VisualBasic.DateAndTimeMicrosoft.VisualBasic.Strings

Microsoft.VisualBasic.Conversion

TheMicrosoft.VisualBasic.Conversion namespacehandlesbasicconversionfunctions forstringsandnumbers.Forabroaderrangeofconversionfunctionality,includingtypes notallowedinVB.NET,referthetoSystem.ConvertnamespaceinthePlatformSDK.

ErrorToStringTheErrorToStringfunctionreturnsahuman-readablestringrepresentingthe numericerrornumberpassedtoit.WhenusingUnstructuredExceptionHandling,this willbethelastnumberreportedbynumberpropertyoftheerrobject.Inprevious versionsofVisualBasic,thesamefunctionalitywasprovidedbytheErrorfunction.

MessageBox.Show(ErrorToString(13))

'Returns"TypeMismatch"

FixandIntTheFixandIntfunctionsremovethefractionalpartofanumber.Forpositivenumbers,bothfunctionsbehavethesame;thefractionisremoved.Thereisnorounding ofnumbers.Thedifferenceiswhendealingwithnegativenumbers.TheIntfunction returnsthefirstnegativeintegerlessthanorequaltothenumber,whereastheFix functionreturnsthefirstnegativeintegergreaterthanorequaltothenumber.Dimx,yassingle

Y=-99.4

X=-99.4

Messagebox.showcstr(fix(y))'Returns-99

Messagebox.showcstr(int(x))'Returns-100Ifthenumberpassedtothefunctionswereapositive99.4,bothMessageboxfunctions wouldreturn99.

HexTheHexfunctionreturnsthestringrepresentationofthehexadecimalvalueofanumber. ThevaluepassedtotheHexfunctioncanbetheShort,Byte,Integer,Long,or Objectdatatype.

MessageBox.Show(Hex(10)) 'ReturnsA

MessageBox.Show(Hex(16)) 'Returns10

MessageBox.Show(Hex("T"))'Error-CannotpassaStringvalue

OctTheOctfunctionreturnsthestringrepresentationoftheoctalvalueofanumber.The valuepassedtotheOctfunctioncanbetheShort,Byte,Integer,Long,orObject datatype.

MessageBox.Show(Oct(10)) 'Returns12

MessageBox.Show(Oct(16)) 'Returns20

MessageBox.Show(Oct("T"))'Error-CannotpassaStringvalue

StrTheStrfunctionreturnsthestringrepresentationofanumber.Aleadingspaceis returnedtorepresentthesign.

MessageBox.Show(Str(10)) 'Returns"10" MessageBox.Show(Str(-10))'Returns"-10"

MessageBox.Show(Str("T"))'Error-CannotpassaStringvalue

ValTheValfunctionreturnsthenumberscontainedinastringasanumericvalueofthe typeIntegerorDouble,dependingonwhetherthereisadecimalplaceinthestring value.TheValfunctionevaluatesastringandstopsatthefirstcharacterthatcannotbe representedasanumberorspace.

MessageBox.Show(Val("123"))

'Returns123

MessageBox.Show(Val("123 4"))

'Returns"1234" MessageBox.Show(Val("123.4"))

'Returns"123.4"

MessageBox.Show(Val("123 4MainStreetSuite194"))

'Returns"1234"

Microsoft.VisualBasic.DateAndTime

TheMicrosoft.VisualBasic.DataAndTime namespacecoverseverythingyoucouldever needtoaccomplishwhenmanipulatingdatesandtimes.Thisnamespaceisvery comprehensiveindateandtimefunctionality.

DateAddTheDateAddfunctionreturnsadatevaluetowhichatimeintervalhasbeenadded.TheDateAddfunctioncontainsthreeparts:

Interval:TheDateIntervalenumerationvalueorstring equivalentrepresentingthetypeofintervalyouareadding.

Number:PositiveornegativeDoubledatatyperepresentingthenumberofintervalsyouareadding.

DateValue:Thedateexpressionrepresentingthedateandtimeto whichtheintervalisadded.

Table8-2:DateIntervalEnumeration

Value String IntervalAdded

DateInterval.Day D Day(integer)

DateInterval.DayOfYear Y Day(integer)

DateInterval.Hour H Hour rounded

DateInterval.Minute N Minute rounded to nearest millisecond

DateInterval.Month M Month(integer)

DateInterval.Quarter Q Quarter(integer)

DateInterval.Second S Second rounded to nearest millisecond

DateInterval.Weekday W Day(integer)

DateInterval.WeekOfYear www Week(integer)

DateInterval.Year yyyy Year(integer)

DimretAsDate

ret=DateAdd(DateInterval.Day, 5,#1/1/2001#)

'Returns1/6/200112:00:00AM

ret=DateAdd(DateInterval.Quarter, 2,#1/1/2001#)

'Returns7/1/200112:00:00AM

ret=DateAdd(DateInterval.Year, 25,#1/1/2001#)

'Returns1/1/202612:00:00AM

DateDiffTheDateDifffunctionreturnsalongvaluerepresentingthenumberoftimeintervals specifiedbetweentwodatevalues.TheDateDifffunctionhasthefollowingfour arguments:

Interval:DateIntervalenumerationvalueorstringexpression representingtheunitoftimebetweenthedate1anddate2values. Table8 - 2liststhevaluesoftheDateIntervalenumeration.

Date1,Date2:Thedateandtimevaluesusedinthecalculation.This firstdatevalueissubtractedfromtheseconddatevalue.

DayOfWeek:AnoptionalvaluefromtheFirstDayOfWeek enumerationthatspecifieswhatdaytouseasthefirstdayofthe week.ThedefaultvalueisSunday.Table 8 - 3 liststhevaluesofthe FirstDayOfWeekenumeration.

WeekOfYear:AnoptionalvaluefromtheFirstWeekOfYearenumerationthatspecifiesthefirstweekoftheyear.Thedefaultvalue isJan1.Table8 - 4liststhevaluesoftheWeekOfYearenumeration.

Table8-3:FirstDayOfWeekEnumeration

Enumeration Value Description

FirstDayOfWeek.System 0 Firstdayof theweekas specifiedin thesystem settingsin thecontrol panel.

FirstDayOfWeek.Sunday 1 Sunday

FirstDayOfWeek.Monday 2 Monday

FirstDayOfWeek.Tuesday 3 Tuesday

FirstDayOfWeek.Wednesday 4 Wednesday

FirstDayOfWeek.Thursday 5 Thursday

FirstDayOfWeek.Friday 6 Friday

FirstDayOfWeek.Saturday 7 Saturday

Table8-4:WeekOfYearEnumeration

EnumerationValue Value Description

FirstWeekOfYear.System 0 Firstweek oftheyear asspecified inthe system settingsin thecontrol panel.

FirstWeekOfYear.Jan1 1 Theweekin which January1st occurs.

FirstWeekOfYear.FirstFourDays 2 Thefirst weekthat hasatleast fourdaysin thenew year.

FirstWeekOfYear.FirstFullWeek 3 Thefirstfullweekofthe year.

DimretAsLong

ret=DateDiff(DateInterval.Day, #1/1/1970#,Now)

'Returns11575

ret=DateDiff(DateInterval.Year, #1/1/1970#,Now)

'Returns31

ret=DateDiff(DateInterval.Second, #1/1/1970#,Now)

'Returns1000108077

ret=DateDiff(DateInterval.Day, #1/1/1970#,Now,_ FirstDayOfWeek.Monday,_

FirstWeekOfYear.FirstFourDays)

'Returns11575

DatePartTheDatePartfunctionreturnsanintegervaluerepresentingtherequestedpartofa date.TheDatePartfunctiontakesfourarguments:

Interval:DateIntervalenumerationvalueorstringexpression representingtheunitoftimeyouarerequesting.Table8 - 2 liststhe valuesoftheDateIntervalenumeration.

DateValue:Thedateandtimevalueusedinthecalculation. DayOfWeek:AnoptionalvaluefromtheFirstDayOfWeek

enumerationthatspecifieswhatdaytouseasthefirstdayofthe week.ThedefaultvalueisSunday.Table 8 - 3 liststhevaluesofthe FirstDayOfWeekenumeration.

WeekOfYear:AnoptionalvaluefromtheFirstWeekOfYearenumerationthatspecifiesthefirstweekoftheyear.Thedefaultvalue isJan1.Table8 - 4liststhevaluesoftheWeekOfYearenumeration.

DimretAsInteger

ret=DatePart(DateInterval.Day, #1/1/1970#)

'Returns1

ret=DatePart(DateInterval.Year, #1/1/1970#)

'Returns1970

DateSerialTheDateSerialfunctionreturnsadatevaluerepresentingtheyear,month,andday. Thetimevalueissetto00:00.TheDateSerialfunctionhasthreerequiredarguments:

Year:Integervaluerangingfrom1to9999.InWindows98and greater,thetwo-digitvalues00through29areconsideredtheyear2000throughtheyear2029,andthetwo-digitvalues30through99 areconsidered1930through1999.Forallotheryearvalues,youshouldalwaysusethefour-digityearvalue.Tobesafe,youshould alwaysusethefour-digityearvalue.

Month:Integervaluerangingfrom1to12.Ifthemonthvalueis outsideofthisrange,themonthvalueisoffsetby1andappliedto Januaryofthecalculatedyear,whichisrecalculatedifnecessary.

Day:Integervaluerangingfrom1to31.Ifthedayvalueisoutsideofthisrange,thedayvalueisoffsetby1andappliedtothefirstdayof thecalculatedmonth,whichisrecalculatedifnecessary.

DateStringTheDateStringpropertyreturnsorsetsastringvaluerepresentingthecurrentdateon yoursystem.

Console.WriteLine(DateString())

'Returns09-07-2001

DayTheDayfunctionreturnsanintegervaluerangingfrom1to31representingthedayof

themonthofthedatepassed.TheDayfunctionhasonerequiredargument: DateValue:Datevaluefromwhichyouwanttoextracttheday.

DimintDayAsInteger intDay=Day("1/15/01") 'Returns15 intDay=Day("Jan152001")

'Returns15

HourTheHourfunctionreturnsanintegervaluerangingfrom0to23representingthehourof theday.TheHourfunctionhasonerequiredargument:

TimeValue:Thedatevaluefromwhichyouwanttoextractthehour.

DimdAsDate DimintHourAsInteger d=#1/15/20011:45:00PM# intHour=Hour(d)

'Returns13

Microsoft.VisualBasic.Strings

TheMicrosoft.VisualBasic.Stringsnamespacehandlesstringmanipulationand formatting.Fromsimpleupper-to-lowercaseconversiontomorecomplexjoiningand splittingofstrings,thenamespaceisextremelycomprehensive.

ASCTheASCfunctionreturnstheintegercharactercodevalueofthefirstletterinastring. Messagebox.ShowASC("A")

'Returns97

Messagebox.ShowASC("a")

'Returns65

ChrTheChrfunctiontakesanANSIvalueandconvertstoastringcontainingthecharacter code.

Messagebox.ShowChr(65)

'ReturnsA

Messagebox.ShowASC(97)

'Returnsa

FilterTheFilterfunctionreturnsazero-basedarraycontainingasubsetofastringarray basedonspecifiedfiltercriteria.TheFilterfunctionhasfourarguments:

Source:Arequiredone-dimensionalarrayofstringstobesearched. Match:Arequiredstringtosearchfor. Include:AnoptionalBooleanvalueindicatingwhethertoreturn

substringsthatincludeorexcludeMatch. Compare:Anoptionalnumericvalueindicatingthekindofstring

comparisontouse.TheCompareMethod.Binaryor CompareMethod.Textconstantscanbepassedtoindicateatextor binarymatchonthematchstring.

DimintXAsInteger DimstrArr(2)AsString

strArr(0)="We" strArr(1)="were"

strArr(2)="Relaxing"

GetCharTheGetCharfunctionreturnsacharvaluerepresentingthecharacterfromthespecified indexinthesuppliedstring.TheGetCharfunctionhastwoarguments:

Str:Arequiredstringexpression. Index:Arequiredintegerexpression.The(1-based)indexofthe characterinStrtobereturned.

DimstrInAsString="Mr.Spock"

Console.Writeline(GetChar(strIn,6))

'Return"p"

InStrTheInStrfunctionreturnsanintegerspecifyingthestartpositionofthefirstoccurrence ofonestringwithinanother.TheInStrfunctionhasfourarguments:

Start:Anoptionalnumericexpressionthatsetsthestartingpositionforeachsearch.Ifomitted,searchbeginsatthefirstcharacter position.Thestartindexis1-based.

String1:Thestringexpressionbeingsearched. String2:Thestringexpressionsought. Compare:Anoptionalsettingindicatingwhethertodoatextual-or binary-basedsearch.

DimstrSearch,strCharAsString

'Stringtosearchin.

strSearch="AaAaBbBbCcDdEe"

'Stringtoseachfor strChar="a"

'Atextualcomparisonstartingatposition1

Console.WriteLine(InStr(1, strSearch,strChar, CompareMethod.Text))

'Returns1

'Abinarycomparisonstartingatposition1

Console.WriteLine(InStr(1, strSearch,strChar,

CompareMethod.Binary))

'Returns2ThereturnvaluefromtheInStrfunctionreturnsazeroif

String1iszerolength String2isnotfound StartisgreaterthanString2

JoinTheJoinfunctionreturnsastringcreatedbyjoininganumberofsubstringscontainedin anarray.Joinhastwoarguments:

SourceArray():Arequiredone-dimensionalarraycontaining substringstobejoined. Delimiter:Anoptionalstringusedtoseparatethesubstringsinthe

returnedstring.Ifomitted,thespacecharacterisused.IfDelimiter isazero-lengthstring,theitemsinthelistareconcatenatedwithno delimiters.

DimstrArr(7),strOutAsStringstrArr(0)="You" strArr(1)="are"

strArr(2)="the" strArr(3)="finest"

strArr(4)="crew" strArr(5)="inthe"

strArr(6)="fleet"

strOut=Join(strArr,"~") Console.WriteLine(strOut)

'ReturnsYou~are~the~finest~crew~in the~fleet~

LCaseTheLCasefunctionconvertsastringtolowercase.

Console.Writeline(LCase("THIS ISCOOL"))

'Returns"thisiscool"

LeftTheLeftfunctionreturnsastringcontainingaspecifiednumberofcharactersfromthe leftsideofastring.TheLeftfunctionhastwoarguments:

Str:Arequiredstringexpressionfromwhichtheleftmostcharacters arereturned. Length:Arequiredintegerexpressionindicatinghowmany characterstoreturn.If0,azero-

lengthstringisreturned.Ifgreater thanorequaltothenumberofcharactersinStr,theentirestringis returned.

DimstrIn,strOutAsString

strIn="C:\MyDocuments\Document1.Doc" strOut=

Microsoft.VisualBasic.Left(strIn, 5) Console.WriteLine(strOut)

'Returns"C:\My"

Len

TheLenfunctionreturnsanintegercontainingeitherthenumberofcharactersinastring orthenumberofbytesrequiredtostoreavariable.

DimstrIn,strOutAsString

strIn="C:\MyDocuments\Document1.Doc" strOut=Len(strIn)

Console.WriteLine(strOut)

'Returns29

LSet,RSetTheLSetandRSetfunctionspadeithertheleftorrightsideofastring. DimstrInAsString="Left"

Console.WriteLine("~"&LSet(strIn,10)&"~")

'Returns~Left ~strIn="Right"

Console.WriteLine("~"&RSet(strIn,10)&"~")

'Returns~ Right~

LTrim,Trim,RTrimThesefunctionsreturnastringcontainingacopyofaspecifiedstringwithnoleading spaces(LTrim),notrailingspaces(RTrim),ornoleadingortrailingspaces(Trim).

DimstrInasString=" ThisisThat "

Console.Writeline(Trim(strIn))

'Returns"ThisisThat"

Console.Writeline(LTrim(strIn))

'Returns"ThisisThat "

Console.Writeline(RTrim(strIn))

'Returns" ThisisThat"

MidTheMidfunctionreturnsastringcontainingaspecifiednumberofcharactersfroma string.TheMidfunctionhasthreearguments:

Str:Thestringexpressionfromwhichcharactersarereturned. Start:A1-basedintegerrepresentingthepositioninStratwhich

theparttobetakenstarts.IfStartisgreaterthanthenumberof charactersinStr,theMidfunctionreturnsazero-lengthstring.

Length:Anoptionalintegerexpressionindicatingthenumberof characterstoreturn.IfomittedoriftherearefewerthanLength charactersinthetext(includingthecharacteratpositionStart),all charactersfromthestartpositiontotheendofthestringarereturned.

Console.WriteLine(Mid("USS Voyager",5))

'Returns"Voyager"

StrCompTheStrCompfunctionreturns–1,0,or1(see Table 8 - 7 ),basedontheresultofastring comparison.Thestringsarecomparedbyalphanumericsortvaluesbeginningwiththe firstcharacter.TheStrCompfunctionhasthreearguments:

String1:Anyvalidstringexpression. String2:Anyvalidstringexpression. Compare:Anoptionalnumericvalueindicatingwhethertousea textualorbinarycompare.

Dimstr1AsString="THEYARETHESAME"

Dimstr2AsString="theyarethesame"

Console.WriteLine(StrComp(str1, str2,CompareMethod.Text))

'Returns0

Console.WriteLine(StrComp(str1, str2,CompareMethod.Binary))

'Returns-1

UCaseTheUCasefunctionconvertsastringtouppercase. Messagebox.show

UCase("enterprise nx-01")

'ReturnsENTERPRISENX-01

Chapter9:DialogBoxesIn This Chapter

IntroductiontodialogboxesTheMessageBoxclassTheMsgBoxfunctionTheInputBoxfunctionTheCommonDialogclass

Introduction to Dialog BoxesAdialogboxaddsinteractivitytoyourapplication.Youcanuseadialogboxtoaccept somevaluefromauser,displaysomeerrormessagetoauser,orperformsome input/outputoperation,suchasopening,saving,orprintingafile.Adialogboxissimplya formwithitsownsetofcontrols,suchaslabels,textboxes,andbuttons.However,unlikeformsyoucannotresizeadialogbox.Youcancreateyourowndialogboxesorusethestandarddialogboxes.Dialogboxesareoftwotypes,modalandmodeless.

Amodaldialogboxmustbeclosedbeforeyoucancontinueyourworkwith thesameapplicationorswitchtoanotherapplication.Amodaldialogbox canbefurtherclassifiedintotwotypes,applicationmodaland systemmodal.

o Anapplicationmodaldialogboxdoesnotallowtheuserto continueworkinginthesameapplicationbeforeclosingthe dialogbox.However,theusercanswitchtoother applications.

o Asystemmodaldialogboxdoesnotallowtheusertowork inanyapplicationbeforeclosingthedialogbox.

Amodelessdialogboxallowsuserstoswitchbetweenapplicationsor continuetoworkwiththerestoftheapplicationwithoutclosingthedialog box.

.NETprovidestheCommonDialogclasstodisplaythestandarddialogboxes,suchastheOpen,Save,andPrintdialogboxes.ItalsoprovidestheMessageBoxclasstodisplayamessagetotheuser.Inaddition,VB.NETprovidestheMsgBoxfunctiontodisplayamessagebox.

The MessageBox ClassYouhaveseenanumberofmessageboxesinanapplication.Thesemessageboxes areusedtodisplayanerrormessageortheresultofacalculation,orprovidetipsand warnings.Theycanalsobeusedforconfirmingoperations,suchasconfirmingthe deletionofafile.Tocarryouttheseoperationsefficiently,themessageboxprovidesthe userwithdifferentbuttons,suchasOK,Cancel,Yes,andNo.YoutoocandisplaymessageboxesinyourapplicationsbyusingtheMessageBoxclass.Thismessagecancontaintext,buttons,andicons.

TheShowmethodYouusetheShowmethodoftheMessageBoxclasstodisplayamessagebox.This methodexistsintwelvedifferentforms.Theseformsdifferfromeachotheronthebasis oftheparameterspassedineachform.Lookatalltheseforms:

MessageBox.Show(Text) MessageBox.Show(Owner, Text) MessageBox.Show(Text, Caption) MessageBox.Show(Owner, Text,Caption)

MessageBox.Show(Text, Caption,Buttons) MessageBox.Show(Owner, Text,Caption,Buttons) MessageBox.Show(Text, Caption,Buttons,Icon) MessageBox.Show(Owner, Text,Caption,Buttons,Icon) MessageBox.Show(Text, Caption,Buttons,Icon,

DefaultButton) MessageBox.Show(Owner, Text,Caption,Buttons,Icon,

DefaultButton) MessageBox.Show(Text, Caption,Buttons,Icon,DefaultButton,

Options) MessageBox.Show(Owner, Text,Caption,Buttons,Icon,

DefaultButton,Options)

InalltheprecedingvariationsoftheMessageBox.Showmethod: Ownerspecifiesthewindowinfrontofwhichthemessageboxwillbe displayed. Textisthemessagetobedisplayedinthemessagebox. Captionisthetexttobedisplayedinthetitlebarofthemessagebox. Buttonsspecifiesthebuttonstobedisplayedinthemessagebox.You

usetheMessageBoxButtonsenumerationtospecifythebuttons.An enumerationisalistofconstants. Iconspecifiestheiconstobedisplayedinthemessagebox.Youuse

theMessageBoxIconenumerationtospecifytheicon. DefaultButtonspecifiesthedefaultbuttonforthemessagebox.You

usetheMessageBoxDefaultButtonenumerationtospecifythe defaultbutton.

Optionsspecifiesthedisplayandassociationoptionsforthemessage box.YouusetheMessageBoxOptionsenumerationtospecifythe options.

ThefollowingstatementdisplaystheuseoftheShowmethod:

MessageBox.Show("Hello World","Sample")ThisstatementdisplaysamessageboxwiththemessageHelloWorld.Sampleis displayedinthetitlebarofthemessagebox.

TheMessageBoxButtonsenumerationTheMessageBoxButtonsenumerationcontainsconstantsthatareusedtospecifythe buttonsforthemessagebox.SomeofthecommonlyusedconstantsareOK,OKCancel, YesNo,andYesNoCancel.Considerthefollowingstatementtounderstandtheusageof theMessageBoxButtonsenumeration:

MessageBox.Show("HelloWorld","Sample",

MessageBoxButtons.OKCancel)

Table9-1:MessageBoxButtons EnumerationConstants

Constant UsedTo

OK Display onlytheOKbutton.

OKCancel Display theOK and Cancel button s.

AbortRetryIgnore Display the Abort, Retry, and Ignore buttons.

YesNoCancel Display theYes,No, and Cancel buttons.

YesNo Display theYesandNo buttons.

RetryCancel Displaythe Retry and Cancel buttons

TheMsgBoxfunctionTheMsgBoxfunctionisasharedmemberofthe Microsoft.VisualBasic._Interactionclass.TheInteractionclasscontains proceduresandmethodsthatareusedtointeractwithobjects,applications,andsystems.Becauseitisasharedmember,youcanusetheMsgBoxfunctiondirectlylikeasystemfunction,aswasusedinpreviousversionsofVisualBasic,orbyspecifyingthe completeclasshierarchy.Thefollowingcodewillhelpyouunderstandthisbetter.

Microsoft.VisualBasic.Interaction.MsgBox("HelloWorld")

issimilarto, MsgBox("HelloWorld")TheMsgBoxfunctiontakesthreeparameters:themessagetobedisplayed,aconstant representingthebuttonsandiconstobedisplayed,andthetitleofthemessagebox. TheMsgBoxfunctionreturnsanintegervalue,whichcorrespondstothebuttonclicked bytheuser.Thesyntaxis

DimretValueasInteger

retValue=MsgBox(sMessage,[nConst],[sTitle])

Intheprecedingsyntax sMessageisthemessagetobedisplayed.Itcancontainupto1,024 characters. nConstisanumericornamedconstantusedtospecifythenumberand

typeofbuttons,icontobedisplayed,defaultbutton,andmodalityofthe messagebox.Todoso,youusetheMsgBoxStyleenumeration. Actually,allthepreviouslymentioneditems,suchasbuttonsandicons, arerepresentedbyanumberandthisparametercontainsthesumofall thesenumbers.Youcanalsousenamedconstantstospecifythis.This parameterisoptional.Ifyouskipit,onlytheOKbuttonisdisplayedinthe messagebox.

sTitleisthestringusedasatitleforthemessagebox.Thisparameter is alsooptional.If youskipthisparameter,thenameof theapplicationis displayedinthetitlebarofthemessagebox.

retValueisanintegerthatcontainsthevalueofthebuttonclickedby theuser.Youcanusethistotrapthebuttonclickedbytheuser.Youcan usetheMsgBoxResultenumerationtotrapthesevalues.

TheInputBoxFunctionTheInputBoxfunctionisasharedmemberofthe Microsoft.VisualBasic._Interactionclass.LiketheMsgBoxfunction,the InputBoxfunctioncanalsobeuseddirectlylikeasystemfunctioninsteadofspecifying thecompleteclasshierarchy.

Microsoft.VisualBasic.Interaction.InputBox("Enteryourname")

Theprecedingstatementissimilartothefollowingstatement: InputBox("Enteryourname")YouusetheInputBoxfunctiontoacceptavaluefromtheuser.Itreturnsthevalue enteredbytheuser.Thesyntaxis

InputBox(sPrompt,[sTitle],[sDefaultValue],[nX],[nY])

Intheprecedingsyntax sPromptistheprompttobedisplayedtotheuser.Itcanholda maximumof1,024characters. sTitleisthetexttobedisplayedinthetitlebaroftheinputbox.Itis

optional.Ifyouskipit,thenameoftheapplicationisdisplayedinthetitle bar. sDefaultValueisthevaluedisplayedinthetextbox(containedinthe

inputbox)asthedefaultvalue.It is optionalandif youomitit, anempty textboxisdisplayed. nXisthehorizontaldistancebetweentheleftedgeoftheinputboxand

theleftofthescreen.Itisoptional.Ifyouomitthisparameter,theinput boxisdisplayedinthehorizontalcenterofthescreen.

nYistheverticaldistancebetweenthetopedgeofthedialogboxandthetopofthescreen.Itisoptional.Ifyouskipthisparameter,theinput

boxisdisplayedatapositionapproximatelyone-thirdofthewaydown thescreen.TounderstandtheusageoftheInputBoxfunction,considerthefollowingexample: DimsVar,sResultAsString

sVar="Entertheusername"

sResult=InputBox(sVar,"Logon","User",50,50) YoucanseetheoutputofthiscodeinFigure 9 - 3 .

Figure9-3: ThesampleoutputIntheprecedingexample,theapplicationpromptstheuserfortheusername.Theinput boxcontainsLogoninitstitlebarandthevalueUserisdisplayedinthetextbox,by default.

Ifyoudonotspecifyanyoftheoptionalparameters,youneedtoretainthe correspondingdelimiter(thatis,comma).Forexample:

DimsVarAsString

sVar=InputBox("Entertheusername","Logon",,50,50)Intheprecedingexample,thedefaultvalueisnotspecifiedintheInputBoxfunction. However,thecorrespondingdelimiter(,)isspecified.Youcanseetheoutputofthis exampleinFigure9 - 4 .

Figure9-4: Thesampleoutput

The CommonDialog ClassFileDialog

ColorDialogFontDialogPageSetupDialog

PrintDialog

Thedetailsoftheseclassesarediscussedinthefollowingsections.

TheFileDialogclassTheFileDialogclassisusedtohandlefileoperations,suchasopeningandsavinga file.Thisclassdisplaysadialogboxfromwhichtheusercanselectafile.Thedialogbox shownbytheFileDialogclassisamodaldialogbox.TheFileDialogclassfurtherconsistsoftheOpenFileDialogclassandthe SaveFileDialogclassesthathelpyoutodisplayOpenandSavedialogboxes, respectively.

TheOpenFileDialogclassTheOpenFileDialogclassprovidesyouthestandardOpendialogboxprovidedby Windows.Youusethisdialogboxtoprovideuserswiththefileselectioncapability.The OpenFileDialogclassprovidesvariouspropertiesandmethodstomanipulatethe Opendialogbox.Table9 - 4describessomeofthepropertiesandmethodsofthe OpenFileDialogclass.

Table9-4:OpenFileDialogClassPropertiesandMethods

PropertyOrMethod Description

Table9-6:ColorDialogclassPropertiesandMethods

PropertyOrMethod

Description

ShowDialog Displaysthe dialogbox.

Color Determines thecolor selectedby theuser.

AllowFullOpen Determines whetherthe usercan addcustom colorstothe dialogbox.

SolidColorOnly Determines whether the usercan usedithered colors.


Multiselect Determines whetherthe dialogbox allows selecting multiple files.

Table9-4:OpenFileDialogClassPropertiesandMethods


ShowReadOnly Determines whetherthe dialogbox displaysa read-only checkbox.

ReadOnlyChecked Determines whetherthe read-only checkboxis checked.

Filter Determines the typesof files that will appearinthe"FilesofType"boxin thedialog box.

FilterIndex Determines theindexof thefilter selectedin thedialog box.

TheSaveFileDialogclassTheSaveFileDialogclassoffersyouthestandardSavedialogboxprovidedby Windows.Youusethisdialogboxtoprovideuserswithfile-savingcapability.The SaveFileDialogclassprovidesyouwithmethodstomanipulatethisdialog.Table9 -5describessomeofthepropertiesandmethodsoftheSaveFileDialogclass.Table9-5:SaveFileDialogClassPropertiesandMethods


ShowDialog Displaysthe message box.

CheckFileExists Determines whetherthe filespecified bytheuser exists.

FileName Determines thefilenameselectedby theuserin thedialog box.

Filter Determines the typesof files that will appearinthe "Saveas fileType"boxinthe dialogbox.

FilterIndex Determines theindexof thefilter selectedin thedialog box.

Figure9-6: AsampleSaveAsdialogboxTheColorDialogclassTheColorDialogclassprovidesadialogboxthatallowstheusertoselectacolorfrom thepaletteandtoaddcolorstothatpalette.Table 9 - 6 describessomeoftheproperties andmethodsoftheColorDialogclass.

Table9-7:FontDialogClassPropertiesandMethods



Color Determines fontcolor selectedby theuser.

Font Determines thefont, style,size, script,and effects.

Figure9-7: AsampleColordialogbox

TheFontDialogclassTheFontDialogclassprovidesadialogboxthatallowsyoutoalterthefont,fontstyle, andsize.Thisdialogboxdisplaysthecurrentlyinstalledfontsonyoursystem.Table9 - 7describessomeofthepropertiesoftheFontDialogclass.

Figure9-8: AsampleFontdialogbox

ThePageSetupDialogclassThePageSetupDialogclassdisplaysadialogboxthatyoucanusetomanipulatepagesettings,suchasmarginsandorientationsandtheprintersettingsofadocument.ThepagesettingsofasinglepagearerepresentedbythePageSettingsclass.The informationforprintingadocumentisrepresentedbythePrinterSettingsclass.The PrinterSettingsclasscanalsomanipulatethesettingsoftheprinterusedforprintingthedocument.Table9 - 8 describessomeofthepropertiesandmethodsofthePageSetupDialogclass.

Table9-8:PageSetupDialogClassPropertiesandMethods



AllowMargins Determines whetherthe margins sectionof thedialog boxis enabled.

AllowOrientations Determines whetherthe orientation sectionof thedialog boxis enabled.

AllowPaper Determines whetherthe paper sectionofthedialog boxis enabled.

Document Determines the documentto getpage settings from.The PrintDocumentclass definesanobjectthatisusedtosendoutput toaprinter.

Figure9-9: AsamplePageSetupdialogbox

Chapter12:ErrorHandlingIn This Chapter

IntroductiontoerrorhandlingTypesoferrorsTry…Catch…FinallyOnErrorGoto

Errors in ProgrammingWhenwritingcode,thereareseveraltypesoferrors,orexceptions,thatcanoccur. DependingonhowyourVisualStudio.NETenvironmentissetup,theseerrorsmayor maynotgetcaught.Table1 2 - 1liststhetypesoferrorsthatcanoccur.Table12-1:TypesofErrors

Type Reason

SyntaxErrors Misspelled keywords or variables. TheVB.NET compiler will normally catch these

Table12-1:TypesofErrors

Type Reasonerrors whileyou are coding, butyou have control overhow much checking youwanttheIDEto do.

LogicErrors Code doesnot actas expected because ofaflaw inthe logicyou have applied.

RuntimeErrors Occur onceyour applicatio nisinproduction.The resultof not handling anunexpectederror.

Figure12-1: ErrornotificationusingOptionExplicitOptionStrictisanotherproject-levelsettingthatcanhelpyouavoiderrors.With OptionStrictsettoON,theIDEwillnotifyyouifthedataconversionyouare attemptingisillegal.Forexample,ifyouaremultiplyingnumbersandthosenumbersare greaterthantheamountallowedforthevariableyouhavedeclared,thecompilerwilllet youknow.Figure12 - 2showstheerrorthatwilloccurifyouattempttosetthevalueofan arithmeticoperationusingashortdatatypetoholdanon-integralnumber.

Figure12-2: OptionStricterrornotificationStructured Exception HandlingNowthatyouhaveagraspofthetypesoferrorsthatcanoccur,youneedtoknowhow totraperrorsthattheIDEdoesnotcatch.Afterall,itcannotdoeverythingforyou.A typicalscenarioforcatchingerrorsmightbecodethataskstheusertoopenafile.Your programwillpopupabox,andtheuserwillhavetotypeinafilename.Ifthefiledoes notexist,orpossiblyitwasmisspelled,yourapplicationwillhavetoreacttothat somehow.Ifyouarenottrappingforexceptions,aruntimeerrorwilloccur,andyour applicationwillcrash.TrappingerrorsinVisualBasicwasalwaysdonewiththeOn ErrorGotostatement.Youwillseethatlaterinthechapter,butnowyouneedtolook atanewandbetterwaytohandleerrors.UsingtheTry…EndTryblocksofStructured ExceptionHandling,youhaveamoreobject-orientedapproachtohandleerrors.The followingcodedemonstratesourFile

Openscenario:

PrivateSubButton1_Click(ByValsenderAsSystem.Object,_

ByValeAsSystem.EventArgs)HandlesButton1.Click

GetFileName(Textbox1.Text) EndSub

PrivateFunctionGetFileName(ByValstrNameAsString)As

String

Try

IfstrName<>""Then

Table12-2:ExceptionClassProperties

Property Description

HelpLink Getsorsets thelocation ofthehelp file associated withthe exception.

HResult Getsorsets HRESULT, acoded numerical valuethatis assignedto aspecific exception.

Return"EverythingisOK" EndIf

Catch

Return"Pleaseenteravalidfilename" Finally

'Dosomecleanupcode

EndTry

EndFunctionYouwillnoticeseveralnewthingshere;theTry…EndTryblock,theCatchstatement, andtheFinallystatement.ThisisthebackboneofStructuredExceptionHandling.

Exceptions.NETruntimehandlesexceptionsandthewaypreviousVBversionshandlederrorsareasfollows:

Exceptionscancrossprocessboundariesandmachineboundaries. Exceptionsarehandledthesamewayregardlessofwhatlanguagethe

applicationwaswritteninorwhatlanguagetheexceptionwillbehandled in. ExceptionsarebasedontheSystem.Exceptionclass. Exceptionscanbetracedtotheoffendingprocedureandlineofcodein

thecallingchainusingtheStackTraceproperty.

Table12-2:ExceptionClassProperties

Property Description

InnerException Getsa referenceto theinner exception.

Message Getsthe string representationofthe error message associated withthe exception.

Source Getsorsets thenameof the application orobjectthatcausedthe exception.

StackTrace Getsthe stacktrace identifying thelocation inthecode wherethe exception occurred.

TargetSite Getsthe methodthat threwthe exception.

Try…Catch…FinallyKnowingthatexceptionswillhappenisonething,butknowingwhattodowhenthey appearisanother.InStructuredExceptionHandling,youusetheTry…Catch…Finally blocktohandleexceptions.Whenreadingtheonlinehelp,theTry…Catch…Finally blockwillappearunder"HandlingProgramFlow,"orsomethingsimilar.Thisistrue becauseyouareactuallycontrollingtheflowofyourprocedureswhileimplementing exceptionhandling.Herearetherulesforhandlingexceptionswith Try…Catch…Finally:

CodethatcancauseanexceptionshouldbeplacedinaTry…EndTryblock.

WithintheTry…EndTryblock,youwriteoneormoreCatchblocksthatrespondtoexceptionsthatmayoccurintheTryblock,attemptingto handletheexception.

Ifyouwantcodetoalwaysexecute,regardlessofanexception,youwritecodeinaFinallyblock.

Chapter13:NamespacesIn This Chapter

NamespacesWritingnamespacesCommonnamespaces

Introduction to NamespacesNamespacesallowclassestobecategorizedinaconsistent,hierarchicalmanner.The.NETFrameworkiscomprisedofhundredsofnamespacesthatallderivefromthebase classSystem.Anamespaceisessentiallyaphonebookforfunctionalityinthe frameworkandiscomprisedoftypesthatyouuseinyourapplications.Thetypescanbe classes,enumerations,structures,delegates,orinterfaces.

Theconventionfornamingnamespacesisasfollows:Thefirstpartofthenamespace,uptotheright-mostdot,isthenameofthe namespace.Thelastpartofthenamespacenameisthetypename.

Ifyouneedtoperformdataaccess,youwouldlooktotheSystem.Datanamespace.To accessSQLServer-specificfunctionality,youwouldreferencethe System.Data.SQLClientnamespace.Touseanamespaceinyourapplication,youusetheImportsstatementattheverytopofyourclassfile.EachImportsstatementdefinesthenamespacesforthatspecificfile; ifyouneedtouseSystem.Datainmorethatonclassfile,youmustspecifyitineach classfile.Anamespacecancontainclasses,structures,enumerations,delegates,interfaces,and othernamespaces.Namespacescanalsobenested,meaningthatanamespacecalled BcanbeinsideanamespacecalledA,andeachnamespacecanhaveanynumberof members.ThefollowingcouldrepresenttheSystemnamespace.NoticehowtheIO namespaceisnestedwithinSystem.

NamespaceSystem

NamespaceIO

PublicClassFileStream

'Functionsthat

'implementstreamIO EndClass

EndNamespace

EndNamespace

Intheclientcode,youwouldreferencethisnamespacelikethis: ImportsSystem.IO

ClassClass1

SubNew()

DimfsasnewFileStream

EndSub

EndClass

Creating NamespacesTocreateanamespace,youusetheNamespace…EndNamespaceblock.Withinthe namespaceblock,youcreateclasses,enumerations,structures,delegates,interfaces, orothernamespaces.Youdonothavetoincludeallofyourcodeinasingle,physical file.Anamespacecanspanmultiplefiles,andevenmultipleassemblies.Thismakesit easyformanydeveloperstobuildasingleapplicationusingthesamenamespace.Forexample,ifyouarewritingabook,andthebookhaslotsofsourcecode,youmaydecide togivethenamespacethesamenameasyourbook.Thenamespaceyouwillbuildhere willbecalledVBBible.Itwilllooklikethis:

NamespaceVBBible

EndNamespace

Namespace ReferenceComponentmodelSystem.ComponentModel—Licensinganddesigntimeimplementationofcomponents.

DataSystem.Data—Dataaccess

System.Data.SQLClient—SQL Serverdataaccess System.Data.OLEDB—OLE DBdataaccess System.Data.XML—XMLProcessing System.XML.Serialization—BidirectionalobjecttoXMLmapping

ServicesSystem.Diagnostics—Provides debuggingandtracingservices System.DirectoryServices—ActiveDirectoryprovider System.Messaging—Microsoft MessageQueuemanagement System.ServiceProcess—Servicestoinstallandrunservice-basedapplications

NetworkingSystem.Net—Programmable accesstonetworkprotocolsSystem.Net.Sockets—Managed accesstoWindowsSockets

GUISystem.Drawing—Access toGDI+functionsSystem.Windows.Forms—Classes thatcreateWindowsFormsbased–applications

SecuritySystem.Security—Access to.NETFrameworksecuritymechanisms System.Security.Cryptography—Cryptographyservices,suchasencoding, decoding,hashing,authenticationanddigitalsignatures

WebServicesSystem.Web—ASP.NETandWebFormssupportSystem.Web.Mail—SMTPmailsendfunctionalitySystem.Web.Caching—Caching frequentlyusedresourcesontheWebserverSystem.Web.Services—Build andmaintainWebServices

Generalapplication System.Collections—Collection support System.IO—FileIOsupportSystem.Text—StringmanipulationandcharacterencodingSystem.Threading—Multithreading support

GlobalizationSystem.Globalization—Internationalizationclasses

Chapter14:Classes and ObjectsIn This Chapter

ClassesModulesOverloadingOverridingConstructorsDestructorsGarbagecollection

Chapter16:COM Interop and MSMQIn This Chapter

IntrotoCOMinteropCallingCOMfrom.NETHandlingerrorsinCOMinteropIntrotoMSMQCreatingqueuesCreatingqueuemessagesReadingqueuemessagesDeletingqueuemessages

Consuming COM from .NETTheCLRexposesCOMobjectstocallersthroughtheRuntimeCallableWrapper(RCW) proxy.TheRCWexposesmetadatatotheCLR,whichallowstheCLRtosuccessfully marshalcallsbetweenmanaged.NETcodeandCOMcomponents.WhenyoudecideyouneedtouseaCOMcomponentinyour.NETapplication,youaddareferencetoyourprojectjustasyoudidinVB6.Whenthecomponentisadded, metadataiscreatedfromthetypelibraryofthecomponentthatisbeingreferenced. Whentheobjectisinstantiatedinyour.NETapplication,itistreatedasanyother.NET classlibrary.Yourcodeactsandlooksthesame.Underthehood,theCLRiscreatingtheRCWfortheCOMobjectandtheCOMobjectitselfismarshalingcallsbackandforth betweenthemanagedandunmanagedprocesses.Figure16 - 1representsanoutside lookattheprocessofinteroperabilitybetweenunmanagedandmanagedcode.

Figure16-1: CominteroperabilitypathGettingthisprocessrollingisquitesimple.Tostart,createaVB6ActiveXDLLproject calledMath,andrenametheClass1toSquare.IntheSquareclass,addapublic functioncalledSquareIt.IfyouhavetakentheMicrosoftVBcourses,youhavedone thisexamplemanytimes.TheSquareItfunctionshouldlooklikethefollowing:

PublicFunctionSquareIt(intXAsInteger,intYAsInteger)AsLong

SquareIt=intX*intY EndFunctionWhenthatisallsquaredaway,goaheadandcompiletheDLL.ThiswillregisteritandmakeitavailabletoourVB.NETapplication.Ifyouareusinganothermachineto compiletheDLL,youwillneedtoregisteritusingREGSVR32.EXEonthe.NET machine.ToregisteracomponentusingtheREGSVR32.EXEutility,simplyopenthe commandpromptandpassthepathargumenttotheutility.IfyoucopiedtheDLLtothe C:\Winnt\System32directory,thentoregistertheDLL,typethefollowing:

C:\Winnt\System32\Regsvr32.exe C:\Winnt\System32\Math.Dll

YouwillbenotifiedwithamessageboxthattheDLLwassuccessfullyregistered.Next,createaVB.NETWindowsFormsapplication.OnthedefaultForm1,addtwotext boxes,alabel,andabutton.TheformshouldlooklikeFigure 1 6 - 2 .

Figure16-2: TheSquareItform

NowyouneedtoaddareferencetotheMathDLLthatyoucompiledearlier.Youcando thisinoneoftwoways:1. FromtheProjectmenu,selectAddReference.2. Right-clicktheProjectnameandselectAddReference.

OncetheAddReferencedialogisopen,clicktheCOMtab,findyourMath.DLLinthe list,highlightitwithyourmouse,clicktheSelectbutton,andthenclickOK.Youwill receiveamessageboxsimilartoFigure16 - 3 .

Figure16-3: Wrappergenerationnotification

ThisistheprocessofcreatingtheRCWforthiscomponent.ClickYesonthedialogbox, andlettheIDEgeneratetheRCWforthisCOMobject.YouwillnowseeyourMath objectinthereferenceslist.Allthatisleftistoconsumetheobject,whichisnodifferentthanconsuminganyother.NETcomponent,thankstotheRCW.Intheclickeventforthebuttononyourform, addthefollowingcode:

DimxAsNewMath.Square()

Label1.Text=x.SquareIt(TextBox1.Text, TextBox2.Text)

Runyourapplication,enteravalueineachofthetextboxes,andclickthebutton.The labelwilldisplayyournewlysquarednumber.Itdoesnotgetmucheasierthanthat.

Microsoft Message QueueMSMQisprobablyoneofthegreatest(andleastused)servers,makingitpossibleto writetrulydisconnectedandscalableapplications.Inthenextpartofthischapter,you learnthemajorcomponentsofwritingapplicationsthatuseMSMQandhowto manipulateMSMQobjects.

WhatisMessageQueue?MSMQisessentiallyanapplicationthatguaranteessendingandreceivingmessages reliably.MessagescanbeanythingfromXMLfilestoADORecordsetstoMicrosoftWord documents.ItdoesnotmatterwhatyousendtoMSMQ,youjustknowthatoncethe messageisinaqueue,itsdeliveryisguaranteed.

WhyMSMQ?

TheneedforMSMQneedstobebuiltintothedesignphaseofyourapplications.Itis notsomethingthatshouldbeanafterthoughtbecauseitisthebackboneofa disconnected,robustapplication.Thefollowingareafewfactorsthatwillmakeyou

choosetoimplementMSMQintoyourdesign: Directcallsbetweenclientsandserversoverconnectionscanfail.

MSMQgivesyoumechanisminwhichthiswillneverbeanissue. Messagescanbesenttoqueueswhenresourcesarenotavailable,such

asotherqueues,andretrievedwhentheresourcebecomesavailable. Messagescanbeprioritized,socertainmessagessuchasfoodorders

willbedeliveredbeforelogfilesorsomethingofanoncriticalnature. MSMQis100%transactional,soitcanbepartofaCOM+transaction,

givingyoutheguaranteeofanallornothingdeliverymechanism. MSMQaccessisbasedonWindowsSecurity,soyouareguaranteedto

beworkingwithinasecureenvironment.

GettingstartedwithMSMQ

BeforeyoudecidetoimplementMSMQ,youneedtomakesurethatitisinstalledonthe serverthatyouintendtosendthemessagesto.Unlessyoudidacustomsetupwhen youinstalledWindows,MSMQwillnotbeinstalled.Therearetwowaystocheckthat MSMQisinstalled:

1. Right-clickMyComputerandselectComputerManagement.Inthe treeviewunderServicesandApplications,youwillseeMessage Queue.Ifyoucandrillintothatnodewithoutreceivinganerrorthat MSMQisnotinstalled,youareallset.

2. FromtheServerExplorerinVisualStudio.NET,drillintotheServersnode.YouwillseeMessageQueuesin thelist.If youcandrillintothe MessageQueuesnode,and you see PublicQueues,PrivateQueues, andJournalQueues,thenMSMQisproperlyinstalled.

Table16-1:User-CreatedQueues

Name Description

PublicQueue Queuesthatarereplicatedthroughoutthenetwork andcanbeaccessedbyotherconnectedsites.

PrivateQueue Queuesthatareavailableonlyonthelocal computer.

AdministrationQueue

Containsacknowledgmentreceiptsofmessages sentinthenetwork.

ResponseQueue Containsresponsemessagesthatarereturnedto thesendingapplicationwhenthemessageis receivedbythedestinationapplication.

Table16-2:System-CreatedQueues

Name Description

JournalQueue Optionallystorescopiesofmessagesthataresent andcopiesofmessagesthatareremovedfroma queue.

Dead-LetterQueue Storescopiesofundeliverableorexpired messages.

ReportQueue Storestherouteamessagehastaken.

PrivateSystemQueue

Storesadministrativeandnotificationmessages thatthesystemneedstoprocess.

Programming MSMQImplementingmessagingintoyourapplicationisquiteeasy.Usingthe System.Messagingnamespace,youhaveallofthemembersthatincorporate messaging.UsingSystem.Messaging,youaregoingtodooneofthefollowingtasks:

CreateanewqueueFindanexistingqueueSendmessagestoaqueueReadmessagesfromaqueue

Table16-3:EnumerationMembers

Member Description

GetMessageQueueEnumerator Createsan enumerator objectfora dynamic listingof public queueson thenetwork.

GetPrivateQueuesByMachineName Retrieves private queuesona machine.

GetPublicQueues Retrieves public queueson thenetwork.

GetPublicQueuesByLabel Retrieves public queueson thenetwork thatmatcha specific label.

GetPublicQueuesByMachine Retrieves public queuesfora specified

Retrieveinformationaboutmessagesinaqueuewithoutactuallyreadingthe message

CreatingqueuesTheCreateconstructorofSystem.Messaginghandlesthecreationofnewqueues.If youareattemptingtosimplysendmessagestoaqueue,youwillnotusetheCreate method,butyouwillusetheSendmethod.Inmostenvironments,Tocreateanewqueue,usethefollowingcode:

IftxtQueueName.Text.Length >0Then

DimqAsNewMessageQueue()

DimstrQAsString=".\Private$\"&txtQueueName.Text q.UseJournalQueue=True

q.Create(strQ,True)q.Close() EndIf

AccessingqueuesIfyoucreatequeuesthroughtheCreatemethod,orifyoumanuallycreatethem throughComputerManagement,youwillneedawaytoreferencequeuesinyourcode. ThereareseveralenumerationmembersintheSystem.Messagingnamespace, dependingonwhattypeofqueuesyouarelookingfor.Table1 6 - 3 showscommon membersoftheSystem.Messaging.MessageQueue classusedforqueueenumeration.

DeletingqueuesTodeleteaqueue,youusetheDeletemethodafteryouhavegottenareferencetoa MessageQueueobject.TheparameteroftheDeletemethodwilltakeeitherafully qualifiedprivateorfullyqualifiedpublicqueuename,somakesureyoureferencethe machinenameandthequeuename.Thefollowingcodewilldeleteaprivateandpublic queuenamed"MyQ".

DimqAsMessageQueue

'DeletesPrivateQueue q.Delete("Server1\Private$\MyQ")

'DeletesPublicQueue

q.Delete("Server1\MyQ")SendingmessagestoqueuesYousendmessagestoaqueueusingtheSendmethod.TheSendconstructoris overloaded,havingparameterssuchasBody,Label,andTransaction.Tosenda message,youwillneedtocreateaninstanceofaqueue,andsetthePathproperty,so theSendwillknowwheretogo.Thefollowingcodewillaccomplishthisfeat.


q.Path="jb650\Private$\MyQ" Ifq.Exists(q.Path)Then

q.Send("Thisisthemessage","TestLabel")

q.Close() Else

MsgBox("TheQueueyouarewritingtodoesnotexist")

EndIf

ReadingqueuemessagesToreadmessagesfromaqueue,youwilleitherPeekintoaqueueorReceivefroma queue.ThePeekmethodreadsthefirstmessageinthequeue,allthetime.Youwould peekintoaqueuetotestfortheexistenceofmessagesandcheckmessageproperties. Peekingintoaqueuedoesnotremovethemessage.Ifyoupeekintothesamequeue multipletimes,thesamemessagewillalwaysbereadunlessanewmessagehasbeen addedwithahigherprioritythanthemessagethatwaslookedatpreviously.The Receivemethodwillreadamessagefromaqueueandremoveitfromthequeue.So onceamessageisreceived,itwillnolongerexistinthequeue.

PeekingintoaqueueThefollowingcodeshowsthePeekmethodinaction. DimstrQAsString=".\Private$\

MyQ"


q.Path()=strQ

Ifq.Exists(q.Path)Then

DimmsgAsMessage

DimformatterAsXmlMessageFormatter=_

CType(q.Formatter,XmlMessageFormatter)

formatter.TargetTypeNames =NewString()_

{"System.String,mscorlib"} msg=q.Peek

Console.Writeline(msg.Label)

Console.Writeline(msg.Body)

EndIfInthisexample,youusedthePeekmethodandassignedtheresulttoanobject declaredasamessage.Becausemessagesarewhatliveinaqueue,youareretrieving propertiesofthemessageitself,notthequeuethatthemessagelivesin.

ReceivingmessagesfromaqueueReceivingmessagesworksalmostlikethePeekmethod,exceptyouusetheReceive methodandyouspecifyatimeoutperiodfortheReceivemethodtofailifnothingisin thequeue.Thefollowingcodewillattempttoreceiveamessagefromthequeuefor threeseconds.

Ifq.Exists(q.Path)Then

DimformatterAsXmlMessageFormatter=_

CType(q.Formatter,XmlMessageFormatter)

formatter.TargetTypeNames=NewString()_

{"System.String,mscorlib"}

DimmsgAsMessage=q.Receive(NewTimeSpan(0,0,3)) Console.Writeline(msg.Label)

Console.Writeline(msg.Body)

EndIfTheReceivemethodwilltakedays,hours,minutes,seconds,andmillisecondsinthe constructor.Ifatimeoutoccurs,anexceptionwillberaisedthatnotifiesyouofthe timeout.ThefollowingCatchstatementwilltrapthetimeouterrorandallowyouto handleitgracefully.

PartIII:VisualStudio.NET:TheIDEforVB.NETChapter17:VisualBasic.NETIDEChapter18:CompilingandDebugging Chapter19:CustomizingChapter20:SourceControl

Chapter17:VisualBasic.NETIDEIn This Chapter

VisualStudio.NETIDECreatingaWindowsFormsapplicationWindowsmanagementbasicsProjectstructureDesigners

The Start Page

Figure17-1: VS.NETStartpage

MyProfile

Basedonthetypeofdevelopmentthatyouwillbedoing,youcancustomizetheIDEto specifickeyboardschemes,windowlayouts,andhelpfilters.IfyouareapreviousVB developer,youmightwanttoselecttheVisualBasicDeveloperprofilesothattheIDEis familiar.ThefollowingarethesettingsthatIchosebasedonmydevelopmentneeds:

Profile:(Custom) KeyboardScheme:VisualBasic6 WindowLayout:VisualStudioDefault HelpFilter:VisualBasicDocumentation ShowHelp:OutsidetheIDE AtStartupShow:VisualStudioHomePage

Thecoolthingisthatifyoufeelthepreferencesyouhaveselecteddonotdoyoujustice, youcanchangethemlateratanytime.Ithinkthatoneofthemostimportantoptionsis theHelpFilter.ThereissomuchinformationintheMSDNLibrarythatitmakeslifealot easierwhenthehelpisfilteredtojusttheVisualBasicinformationthatyouneed.

GetStarted

Themostrecentapplicationlistisoffered.Asingleclickwiththemouseonarecent projectwillopenyourdevelopmentsoyoucanbeginusingtheselectedproject.Youcan alsoselectOpenExistingProjectifanapplicationthatyouhaveworkedonisnotinthe list.CreateNewProjectwillstartanewproject,andReportaVisualStudio.NETIssue willtakeyoutotheWebtoreportaproblemortosubmitabugreport.

What'sNew

ThispageofferslinkstothelatestservicepackupdatesforVisualStudio.NET,linksto partnerresourcesontheWeb,andproductinformationonVisualStudio.NETproducts.

OnlineCommunity

Foryears,thebestresourceforVisualBasicdevelopershasbeentheonlineofferings. FromtheMSDNWebsitetonewsgroups,ifyoueverrunintoaseriousissue,expert helpisalwaysonlinesomewhere.ThenewIDEnowintegratesimportantWebsitesand newsgroupsforyou,soexperthelpisjustasingleclickaway.

Headlines

TheMSDNOnlinehomepageisintegratedintotheIDE,soallofthelatesttechnical articles,news,andtraininginformationareatyourdoorstep.

SearchOnline

TheMSDNOnlineLibraryinavailableforquickaccesswhentheanswersmightnotbein thehelpfilesinstalledonyourmachine.

Downloads

Thelatestdownloadsandadd-onsavailablefor VisualStudioandrelatedproductsare availablehere.Thisfeatureis greatbecauseyouonlyneedto lookata singleareafor anythingnewthatisavailable.

WebHosting

LinkstoISPsthatoffer.NEThostingareofferedinthisoption.Averystrongwordof caution:Yougetwhatyoupayfor,sobewaryof"free"hostingandverylow-priced hosting.Theservicemaynotbewhatyouareusedto(Iamspeakingfrompersonal experienceusingthisfeature).

Your First Visual Basic .NET SolutionNowthatwehaveexploredtheVisualStudio.NEThomepage,let'sgothroughtheIDE anddiscussitsfeatures.Thebestwaytoaccomplishthisistocreateanewsolution,and thendrillintothefeaturesVisualStudiooffers.

Tocreateanewsolution:1. FromtheFilemenu,clickNew Project(seeFigure17 - 2 ).TheNew

Projectdialogboxwillappear.TheNewProjectdialogboxisbrokenup intotwopanes,ProjectTypesandTemplates.Forourpurposes,wewill concentrateontheVisualBasicProjectsfolderintheProjectTypes pane.

Figure17-2: CreatinganewprojectThefollowingtemplatesareavailablethroughtheTemplatespane:

WindowsApplication:CreateaWindowsForms-based application ClassLibrary:CreateaClassLibrarytouseinanother

application

Table17-2:FileExtensions

File Extensi on

Description

XML XMLDocument.

XSD XMLSchemaFilewithoutgeneratedclasses.

TDL TemplateDescriptionLanguageFile.

VB WindowsForm,Control,Class,orCodefile.

RPT CrystalReportsDesignerfile.

HTML HTMLsourcefile.

XSLT XMLfilecontainingtransformationinstructionsforXMLandXSDdocuments.

CSS CascadingStyleSheetusedforHTMLpagestoapplystyles.

VBS VBScriptsourcefile.

WSF WindowsScriptingsourcefile.

JS Jscript.NETsourcefile.

CS C#sourcefile.

ASPX WebApplicationform.

ASP ActiveServerPagesourcefile.

ASMX WebServicesourcefile.

DISCO DynamicDiscoveryDocument,sourcefilethatenumeratesWebServicesandSchemasinaWebproject.

ASCX ASP.NETusercontrol.

CONFIG Applicationspecificconfigurationfile.

WindowsControlLibrary:CreateWindowsForms- basedcontrols WebApplication:CreateaWebServer–based ASP.NET-

basedapplicationcomprisedofstaticor dynamicHTMLpages WebService:CreateaWeb-basedServicetobe

consumedbyanyapplicationthatcancommunicateover theHTTPprotocol WebControlLibrary:CreateWeb-basedcontrols ConsoleApplication:Createacommand-line application WindowsService:CreateaWindowsService EmptyProject:EmptyWindowsApplicationproject EmptyWebProject:EmptyWebserver-based application ImportFolderWizard:Createanewprojectbasedon anexistingapplication

2. SelecttheWindowsApplicationtemplate.3. TypeaNameforyourapplication.Forourpurposes,typeHelloWorld, thedefactostandardforallfirst-

timeprojects.4. FortheLocation,youcanacceptthedefault,whichisyourMy

Documentsfolder.Ifyouwanttostoreyourprojectfileselsewhere, simplyclicktheBrowse…buttonandselectanewlocation.

5. ClickAddtoSolutionorCloseSolution.Thisoptionallowsyoutoeitheraddyournewprojecttotheexistingsolution,orclosetheexisting solutionandstartanewone.AnexamplewouldbeaddinganewWeb ServiceapplicationtoyourexistingVB.NETsolution.

6. Ifyouareaddingtoanexistingsolution,youcanspecifyanalternate directoryandsolutionnameforyournewprojectbyenteringavaluein theNewSolutionNametextbox.

7. ClickOK.

FileextensionsAllofthefileextensionsforVisualBasic.NEThavebeenchangedfromprevious versionsofVisualBasic.Itisimportanttounderstandwhattheextensionsareandwhat theymean.Table1 7 - 2describeseachfileextension.

Table17-2:FileExtensions

File Extensi on

Description

XML XMLDocument.

XSD XMLSchemaFilewithoutgeneratedclasses.

TDL TemplateDescriptionLanguageFile.

VB WindowsForm,Control,Class,orCodefile.

RPT CrystalReportsDesignerfile.

HTML HTMLsourcefile.

XSLT XMLfilecontainingtransformationinstructionsforXMLandXSDdocuments.

CSS CascadingStyleSheetusedforHTMLpagestoapplystyles.

VBS VBScriptsourcefile.

WSF WindowsScriptingsourcefile.

JS Jscript.NETsourcefile.

CS C#sourcefile.

ASPX WebApplicationform.

ASP ActiveServerPagesourcefile.

ASMX WebServicesourcefile.

DISCO DynamicDiscoveryDocument,sourcefilethatenumeratesWebServicesandSchemasinaWebproject.

ASCX ASP.NETusercontrol.

CONFIG Applicationspecificconfigurationfile.

Back to the IDENowthatyouunderstandthesolutionandprojectstructure,andthefilesthatarepartof aproject,let'sgobacktotheIDEandgointodetailswhileexploringourHelloWorld application.

AutoHideThenewAutoHidefeatureallowsyouto"hide"windowsfromthemainIDEwhileyouaredevelopingapplications.EverywindowthatappearsintheIDEhastheAutoHidefeature.TotoggleAutoHideonandoff,clickthepushpinbutton(seeFigure17 - 3)onthetoolbarforeachwindowyouwanttohide.Whenawindowishidden,atabreplacesthelocationofthewindow,whichallowsyoutoclickthetabtoviewthewindow.

Figure17-3: AutoHidepushpin

TabbeddocumentsInthepast,youhadtheWindowpull-downmenutoswitchbetweenopenwindowsinthe IDE.WithVisualStudio.NET,thereisthetabbeddocumentthemethataddsatabtothe topofthemainwindowforeachdocumentorfilethatyouhaveopen(seeFigure 1 7 - 4 ). ThisincludestheMSDNHelptopicsthatwepreviouslylookedat,theobjectbrowser,the Startpage,CodeFile,forms,oranypreviouslyopenedwindow.Toswitchbetweenopen documents,simplyclickonthetabthatrepresentsthedocumentyouwanttoopen.To closeadocument,ortonavigateforwardandbackwardwithinopendocuments,usethe buttonsontheupperright-handcornerofthemainwindow,whichgivefurthernavigation control.TheCtrl+Tabkeycombinationwillnavigateopenwindowsinthemainworkspace.ThistechniqueisidenticaltotheAlt+Tabkeycombinationthatweusetonavigateopenwindowsintheoperatingsystem.

Figure17-4: Tabbeddocumentfeature

DockablewindowsAllwindowswithintheIDEaredockabletoanyedgeoftheIDE.Simplydraganywindow towhateverlocationyouwantittoreside,anditwilllockintoplace.Ifyouhavepreviouslymadethewindowauto-hide,itwillnowauto-hideinitsnewlocation.ThecombinationofAutoHidewithdockablewindowsallowscompletecustomizationofyourIDEworkspace.

FavoritesSimilartoFavoritesinyourWebbrowser,anydocumentinyourIDEcanbeaddedto yourFavorites,aswellasanyWeb-baseddocument.

Multiplemonitor supportThiscoolnewfeatureallowsmultiplemonitorsupportwiththeIDE.Youcannowhave windowsspreadacrossmultiplescreens,furtherenhancingyourproductivity.Thisis,of course,basedonthetypeofvideocardthatyouareusing.Youcannotrunacrossover cablebetweentwocomputersandlikemagichavemultiplemonitors;youwillneedto investinafancyvideocardwithmultiplevideooutputs.

Windows,dialogs,andmorewindowsWenowdrillintothewindowsthatmakeuptheIDE,thetoolbars,thedrop-downmenus, andallthecoolthingsthatmakeupournewenvironment.Becausewehavethe HelloWorldapplicationopen,everythingthatyouareabouttoreadaboutshouldbe visible.Ifanyofthefollowingwindowsthatwedrillintoarenotvisible,youcangetto

thembyselectingtheViewmenu,asFigure17 - 5 demonstrates.

Figure17-5: ViewMenuwithotherwindowsIfyourefertoFigure1 7 - 4 ,youcanseeallofthepossiblewindowsthatyoucanopenin theIDE.Let'sgothrougheachoneandgivesomebackgroundanddetails.

SolutionExplorerSimilartotheProjectExplorerinVB6,theSolutionExplorer(seeFigure17 - 6 )containsa listofallofthefilesassociatedwithyourcurrentsolution.ThroughtheSolutionExplorer, youhavetotalmanagementofyourprojectanditscorrespondingfiles.Solutionsmay containseveralprojects,writteninseverallanguages,usingseveraldifferent technologies.Itistrulyaglobalviewofyoursolution.AsinVisualStudio6,allproject optionsareavailablebyright-clickingwithintheSolutionExplorerandbringingupthe contextmenu.Becauseeachpartofasolutionisdifferent,theoptionsavailabletoyouwillbedifferentdependingonwhatyouselect

Figure17-6: SolutionExplorer

andright-click.Ifyouright-clickonaProjectname,thenProjectoptionssuchasBuild, AddReference,andSaveAswillappear.Ifyouright-clickonaFormoraCodemodule, optionssuchasOpen,ViewCode,orViewDesignerwillbeavailabletoyou.Itisagood ideatoexploreeachoftheoptionswhenyoufirststartusingthisnewIDEtobecome moreproficientinSolutionManagement.

ClassViewTheClassViewwindowisahigh-levelviewofalltheclassesandobjectsinyour solution.FromtheClassView,youcanretrievedefinitionsofeachobject,itsproperties, andmethodswithasimpledouble-click.Iftheclasshasmethodsthatexistinyour application,double-clickingontheobjectwillbringitscodewindowupinthemain workspace.ThereisahandytoolbarontheClassViewwindowthatallowsdifferentsort optionsforfastaccesstoobjects.

ServerExplorerTheServerExplorer(seeFigure17 - 7 )isacentrallocationtomanageallserversand server-basedservicesfromwithintheVisualStudio.NETIDE.Becausethewholeidea ofthe.NETplatformissharedservicesamongmanydifferentservers,thereneedstobe aplacetolocateandmanagetheseservers.TheServerExplorerallowsacentralviewofallserverresources,anydataconnectionsthatyouhaveforyourcurrentsolution,e-mailconfiguration—particularly Exchange2000configuration—andWebService management.

Figure17-7: ServerExplorer

Thefollowingisalistofthetop-levelnodesintheServerExplorerandthepurposeof eachnode: CrystalServices:InstalledCrystalReportoptions. EventLogs:Application,Security,andSystemEventlogsforthe attachedserver. LoadedModules:ListoftheprocessesandloadedDLLsonthe

selectedserver.Theverycoolthinghereisthatthroughthe System.Diagnostics.Process classlibrary,youareexposedtothe propertiesoftheprocesses.Soifyoufeelitnecessary,youcanmodify anyoftheexposedread/writepropertiesthroughPropertieswindows.

ManagementData:ListofinterfacesavailablethroughWindowsManagementInstrumentation.Again,aninsighttoservicesand read/writepropertiesoftheconnectedserver.Forexample,Idrilled intoWin32_Server,LogicalDiskManager,allthewayintomy ComputerName,andmodifiedtheSystemStartupDelayproperty to10.NowwhenIreboot,theOSChoicesmenuisat10seconds insteadof30.

MessageQueues:Listofavailablequeuesandtheircorresponding messages.MessageQueuemustbeinstalledforthistowork.This wouldbethesameviewthatyoucanretrievefromComputer Managementsnap-in.

PerformanceCounters:ListofallavailablePerformanceCountersfortheselectedserver.Thelistishugecomparedtowhatweareused to.Therearehundredsofnewcountersfor.NETalone.Forexample, wenowhaveacountertotrack.NETCLRLOCKSandILBytes JITted/sec.

Processes:Listofrunningprocessesontheselectedserver. Services:Listofrunningservicesontheselectedserver. SQLServerDatabases:Listofdatabasesontheselectedserver.

LiketheDataViewwindowofpastVisualStudioversions,youare openeduptoallofthefunctionalityoftheSQLServerEnterprise Manager.ThisisaveryrobustCOMinterfacethatalleviatestheneed

to haveEnterpriseManageropen.Fromthisview,youcanadd,edit, anddeletetables,views,storedprocedures,databasediagrams,and functions.

WebServices:ListofWebServicesbyProjectandFilewithwhichtheywerepublishedon the selectedserver.Fromthis view,youcan immediatelyaddareferencetoaWebServicetoyourprojectwitha right-clickorbysimplyusingdraganddropintoyourcodewindow.

DataConnections:SimilartotheSQLServerDatabasesnode,youcanaddconnectionstoanydatabaseorserverproviderthathasan installedOLEDBprovideronyoursystem.Thisallowsyoutoconnect toserverssuchasOracle,DB2,Exchange,andActiveDirectory.

PropertieswindowThePropertieswindowallowsyoutomodifyatdesigntimethepropertiesofanyobject thatiscurrentlyselectedinthemainworkspace.IfyouareaVB6developer,youwillbe familiarwithworkingwiththePropertieswindow.Itisthesinglemostimportantwindow intheIDEforcustomizingyourapplicationatdesigntime.Thedefaultviewforthe PropertieswindowistodisplaypropertiesbyCategory;thiscanbechangedtoanalphabeticalviewofpropertiesbyclickingthealphabetictoolbarbuttonontheProperties window.Youcanalsoviewthepropertiesofanycontrolonthecurrentformbyselecting itfromthedrop-downlistjustabovethetoolbar.AsaVBdeveloper,regardlessof whetheryouaredevelopingaWindowsForms–basedapplicationoraWebForms–basedapplication,youarealwaysmodifyingpropertiesofobjectstomaintainthedesiredlookandfeelofyourapplication.UsingthePropertieswindowissomethingthatyoudo about10,000timesaday.GetyourselffamiliarwiththePropertieswindowandeach object'sproperties,especiallyifyouareanexperiencedVBdeveloper,becausethe changestopropertiesofallobjectsinVisualStudio.NETwillsurpriseyou.

ToolboxTheToolbox(seeFigure1 7 - 8 )containstheobjectsandcontrolsthatcanbeaddedto WindowsFormsapplicationsandWebFormsapplications.TheToolboxhasavertical tabbedthemethatallowsquicknavigationbetweenthedifferenttypesofobjectsor controlsthatyouwanttoaddtoyourforms.Bydefault,theToolboxdisplaystheData, Components,WindowsForms,ClipboardRing,andGeneraltabs.Aright-clickonthe ToolboxwilldisplayoptionsfortheToolbox.ShowAllTabswilldisplaytheremainderof thetabsthatarenotdisplayed.Ifyouselectthisoption,youwillseethatthereareabout20differenttabs,rangingfromXSDSchemastoUMLShapes.ToplaceaToolboxitem ontoaform,simplydragtheselectedcontroltothelocationoftheformwhereyouwant thecontroltoreside.Youcanalsodouble-clickonacontroltoplaceitatthelastcursor positionontheform.Oncethecontrolisontheform,youcanthenmoveittoany locationontheformbyclickingonthecontrolanddraggingitwithyourmouse.

Figure17-8: TheToolbox

Ifyouhavecodesnippetsthatyouuseacrossmanyprojects,orthereiscodethatyou don'twanttotypeeverytimeyouneedit,youcanaddthatcodetotheToolbox.Mygoal inlifeistowriteaslittlecodeaspossible,soIhavetonsofcodesnippetsstoredinthe Toolbox.

ToaddcodesnippetstotheToolbox:1.IntheCodewindow,highlightthecodeyouwanttoaddtothe

Toolbox.2.DragtheselectedcodetotheGeneraltab.3.Right-clickontheToolboxandselectRename,andgivethenewly

addedcodesnippetameaningfulname.

YoucandoallToolboxcustomizationwitharight-click,sogoaheadandlookatthe menuoptionsavailablewhenyouright-clickontheToolbox.

MacroExplorerWiththeMacroExplorer,youcanwritemacrosthatcustomizeyourIDEorautomate tasks.TheVisualStudio.NETIDEhasitsownobjectmodel,whichisverycomplete,so youcanautomateprocesseswithintheIDEusingtheMacroIDE.TogettotheMacro IDE,youcandouble-clickonanyofthemacrosthatalreadyexistintheMacroExplorer, oryoucanselectAdd,Edit,orDeletefromtheright-clickcontextmenuwithintheMacro Explorer.Figure17 - 9 displaystheMacroIDE.

Figure17-9: MacroIDE

ObjectBrowserTheObjectBrowser(seeFigure1 7 - 1 0 )isoneofthemostpowerfulwindowsinthe VisualStudioIDE.TheObjectBrowserallowsyoutovieweveryobjectinthecurrent solutionandtheirpropertiesandmethods.Brokenupintotwopanes,theleftpane,or ObjectsPane,displaysahierarchicallistofallobjectsinyoursolution(classes, interfaces,structures,types,namespaces,andsoon).Therightpane,orMembers Pane,displaystheproperties,methods,classes,enumerateditems,variables,and constants.Whenyouselectamemberintherightpane,theDescriptionPaneatthe bottomoftheObjectBrowserdescribesthememberandgivesyouanexampleofthe syntaxthatyouwilluseifyouplanonusingthemember.Thisincludesany dependencies,variables,andadditionalhelpdescriptionthatmayhavebeencompiled withtheobject.TheBrowsedrop-downonthetopoftheObjectBrowserenablesquick navigationtotheloadedobjectsinyourproject,soyoucanlimitthelistofobjectsinthe leftpanetoaspecificobjectinyourproject.TheCustomizebuttonenablesyoutoadd additionalcomponentstotheObjectBrowserortoremovecomponentsthatcurrently existintheproject.IfyouchoosetoaddnewcomponentstotheObjectBrowser,allof the.NETFrameworkandCOMcomponentswillbeofferedtoyouinanalphabeticallist. TheFindbuttonontheObjectBrowsertoolbargivesyouaquicksearchfunctionalityto siftthroughthehundredsofobjectsthatmaybeinyourproject.

Figure17-10: ObjectBrowser

TasklistThetasklistisafamiliarsiteforVisualInterDevdevelopers.Itisacentralizedareathat helpsyoutomanagetaskswithinyoursolution,giveyouerrordetailswhenyoucompile yourcodeorasyouentercode,andithelpsyouself-documentyourprojects.Thereare severalpredefinedtokensthathelpyouself-documentyourcode.TheyareTODO, UPGRADE_TODO,andUPGRADE_WARNING.Byenteringthesetokensafterthecomment symbol(thesinglequote),tasksareautomaticallyaddedtothetasklistforyou.When youneedtogobacktoatokenthatyouadded,justdouble-clicktheiteminthetasklist andtheappropriatesectionofcodeisbroughtupinthemainworkspace.Forerrors,the behavioristhesame.Ifthereareerrorslisted,simplydouble-clickthetasklistitemandyouaretakentotheoffendingline.YoucanaddcustomtokensbyselectingToolsOptionsanddrillingintotheTasksoptionsasFigure1 7 - 1 1 shows.

Figure17-11: Tasklistoptions

CommandwindowTheCommandwindowisusedforexecutingcommandsdirectlyintheVisualStudio.NETenvironment,bypassingthemenusystem,orforexecutingcommandsthatdonot appearonanymenu.

OutputwindowTheOutputwindowdisplayscompiler-specificinformationwhenyoubuildyourprojector solution.TheOutputwindowwilldisplaybuilderrors,librariesthatareloaded,andother detailsofthebuildprocess.

DebuggingwindowsIfyouarelikeme,youconsistentlyamazeyourselfbywritingerror-freecode.Iftheslight chancearisesthatyouneedtouseanyofthepowerfuldebuggingfeaturesinVisual Studio.NET,therearefivewindowsthatassistyouwiththisatruntime.Figure1 7 - 12displaystheavailablewindowsfordebugging:theBreakpoints,Autos,Locals,Watch, andCallStackwindows.Chapter1 8 talksaboutdebuggingindetail,sowewillnot duplicatethatefforthere.

Figure17-12: Debuggingwindows

TheCodeEditorThecodeeditor(seeFigure17 - 1 3 )iswhereyouspendmostofyourtimewritingVB.NETfunctionsandprocedures.Thecodeeditorisprobablythemostimpressivefeature

ofVisualStudio.Withfeaturessuchasspellchecking,Auto-complete,wordand statementcompletion,andAuto-listmembers,thecodeeditorassistsyouineveryfacet ofyourcoding.

Figure17-13: Thecodeeditor

Youcanopenthecodeeditorinseveralways,basedonyourpreference: Youcandouble-clickonanobjectonaformintheWindowsForms

designer,whichwillbringupthecodeeditor. Youcanclickthe"viewcode"buttonontheSolutionExplorertoolbar,

whichisthefirstbuttononthattoolbar. Youcanright-clickanywhereintheformsdesignerandselectViewCode fromthecontextmenu.

BecausetheIDEhasthetabbeddocumentsfeature,youcanhaveasmanycodeeditorwindowsopenasyoulike.Whenafileisopen,suchasaclassfile,form,orXML document,theyarelistedintabsacrossthetopoftheeditorwindow.Figure1 7 - 4 earlier inthechaptershowedthetabbeddocumentfeature.

WiththeinventionofAuto-complete,Auto-listmembers,andspellcheckinginthecode editor,youdonotevenhavetoknoweven70%ofthelanguagetogetapplications written.

AutoList Membersand AutoCompleteAutoListMembersandAutoCompletearefeaturesthathelpyoudiscoverobject membersandfinishoffobjectreferenceswhilecoding.Thisfeatureworksinconjunction withtheImportsstatementsatthetopofyourclassfiles,andwiththebuilt-in namespacesthatarepartofeachclassfile.Byimportinganamespaceintoyourclass, theeditorbecomesawareofitsexistenceandmakesitsproperties,methods,andeventsavailableintheformofdrop-downlistsasyoureferencethoseobjects.Oncealistofmembersforanobjectappears,youcanscrollthroughthelist,orstarttypingthe memberyouarelookingfor,andonceitishighlighted,pressingthespacebarorthe Enterkeywillcompletethestatementforyou.Figure17 - 1 4 isanexampleofAuto Completeinaction.

Figure17-14: AutoCompleteinaction

WithAutoComplete,itisnearlyimpossibletomakeincorrectobjectreferences, declarations,ortypingmistakes.

SpellcheckingSpellcheckinginMicrosoftWordisthemainreasonmostofuslooksosmartwhenwe typeletters(orwritebooks).Withoutthisfeature,Iwouldpersonallyneedtohireatypo editortoredoallofmywork.Inthecodeeditor,youhavethesamesortofspell-checking featurethatWordoffers.Whenyoudeclarevariablesinthecodeeditor,theyarecheckedagainstreferencestothosevariablenamesasyouarecoding.Ifyou accidentallymisspellavariablereference,theeditorwillinformyouofthismistakewitha squigglylineundertheoffendingcode.Figure17 - 1 5 givesanexampleofthespell checkerinaction.

Figure17-15: Thespellcheckerinaction

Designers

Thereareseveraldesignersthatmakeupthe"visual"partofworkingintheIDE. DesignersgiveyouasurfacetocreatethegraphicalfrontendofASP.NETapplications andWindowsFormsapplications.Therearealsodesignersthataidindatabase creation,querygeneration,andXMLediting.

WindowsFormsdesignerTheWindowsFormsdesignerisusedtocreateforms-basedapplications.Byaddinga newformtoyourproject,youcandraganddropcontrolssuchastextboxesorlistboxes ontotheformtovisuallycreateyourGUI.WhenworkingontheFormsdesigner,selectingobjectsontheform,ortheformitself,changesthePropertieswindowsto displaythepropertiesforthatobject.

WebFormsdesignerTheWebFormsdesignerbehavesexactlyliketheWindowsFormsdesigner.The differenceisthetypeofapplicationyouaredeveloping.Ifyouaredevelopingan ASP.NETapplication,youwillbeusingtheWebFormsdesignertomodifythelookand feelofyourASPXfiles,whichmakeuptheuserinterfaceofanASP.NETapplication.

XML designerTheXMLdesignerisusedtoeditandcreateXMLandXSDfiles.TheXMLdesignerhas threeviews:SchemaView,XMLSourceView,andDataView.

SchemaView

TheSchemaViewallowsyoutovisuallydesignandeditXMLschemas.Youcancreate schemasbydragginganddroppingtablesfromdatabaseconnectionsintheServer Explorer,oryoucanaddnewattributesandelementsintheeditor.TheSchemaView alsoallowsthecreationofADO.NETdatasets.

XMLSourceView

TheXMLSourceViewistheeditorforviewingandcreatingXMLfiles.Theeditoralso sharesthesamefeaturesofthecodeeditor,suchasauto-completeandauto-list members.

DataView

TheDataViewissimilartotheTableViewofadatabasetoolsuchasMicrosoftAccess orSQLServer.UsingtheDataView,youcanviewandeditXMLdatainafamiliartable- likefashion.YoucanalsogenerateandviewschemadefinitionsbasedonXMLdata beingdisplayedoreditedinthedataviewwindow.

DatabasedesignerTheDatabasedesignerisafull-fledgeddatabasecreationtool.WiththeDatabase designer,youcanadd,edit,anddeletetables,indexes,views,storedprocedures,and tablerelationshipsinaSQLServer,Oracle,oranydatabaseforwhichyouhavethe correctOLEDBproviders.

QuerydesignerTheQuerydesignerallowsthecreationofcomplexqueriesbydragginganddropping tablesfromadatabaseconnectionontothedesignersurface.Thelookandfeelisthe sameastheviewdesignerinSQLServerEnterpriseManagerandtheQuerydesignerin previousversionsofVisualStudio.

ComponentdesignerTheComponentdesignerallowsforthecreationofnon-graphicalmiddle-tier components.DraggingobjectsfromtheComponentstaboftheToolboxontothe designersurfaceallowsrapiddevelopmentofserver-basedobjectsbysettingproperties onobjectsthroughthedesigner,avoidingsomeofthecodingthatwouldnormallybe neededformiddle-tierandservercomponents.

UserControlDesignerTheUserControldesignerallowsforthevisualcreationofcontrolsthatcanbereused throughoutyourASP.NETapplications.LikeincludefilesinASP,ausercontrolcanbe placedontoanASPXpageanditsfunctionalityiscompletelyencapsulatedwithinthe controlitself.Thedifferencebetweenincludefilesandusercontrolsisthatauser controlcanbevisuallycreatedusingthedesigner,andhasitsowncode-behindpages.

Chapter18:CompilingandDebuggingbyRobTeixeira

In This ChapterCompilingyourcodeConditionalcompilationDebuggingDebuggingtoolsDebugandTraceobjects

Compiling Your CodeTwo scenarios exist for running your code. One is running your code from the development environment so that you can test what you are writing (runninginDebug mode), and the other is producing the binary files that will be placed into production or release. In either case, the source code files must be compiled. This process is called building.

Builds are controlled by build configurations. There are two levels of build configurations. One is the solution level, which affects abuild of all the projects in the solution, and the other is project level, which affects build settings for the individual projects in the solution.

Solution build configurations

There is always one active build configuration for the open solution. This is shown in a drop-down list on the Standard toolbar, which also allows you to select the active build configuration. You can also select the active build configuration, as well as define new configurations, by selecting the Configuration Manager command in the Build menu. This same command is a vailable from the context menu (opened by a secondary click) of the Solution item in the Solution Explorer. This command displays the Configuration Manager dialog box(seeFigure1 8 - 1 ).

Figure18-1: ConfigurationManagerdialogbox

Projectconfigurations

Eachprojectinthesolutionhastwosetsofproperties,onesetthatiscommonandone setthatisdefinedforeachconfiguration.Initially,allVB.NETprojectsstartoutwithonly DebugandReleaseprojectconfigurations.AsageneralruleinVisualStudio.NET,there isoneprojectpropertysetforeachcombinationofConfigurationandPlatform.Toaccessthepropertiesforaproject,selectaprojectandclickthePropertiescommandintheProjectmenu.Alternately,youcanusethePropertiescommandinthecontext menuofanyprojectitemintheSolutionExplorer.ThisopenstheProjectProperties dialogboxasshowninFigure18 - 3.Thecaptionofthedialogboxisintheformof ProjectNamePropertyPages.

Figure18-3: ProjectPropertiesdialogbox

DebuggingoptionsUsetheStartActiontotelltheenvironmentwhattodowhenrunningaprojectfrom withinthedesignenvironment.StartProjectsimplyrunstheproject.StartExternal Programisusefulforlibrarytypeprojects,andstartsanotherprogramthatusesthis libraryproject,allowingyoutodebugthelibrarywiththeotherprogramastheclient. StartURLopensthebrowserandnavigatestothegivenURL.ThegivenpageorASP scriptthenactsastheclienttothelibraryproject.

BuildThispropertypageallowsyoutospecifygeneralbuildoptionsfortheproject.Selectthe BuildnodeunderConfigurationPropertiestodisplaythispage.Thesebuildoptionsare dependentontheprojectconfiguration,incontrastwiththeBuildoptionsontheCommon Propertiesfolder.

Specifythedirectoryyouwanttheresultingcompiledfiletobeplacedinbytypingitin theOutputPath.

CheckGenerateDebuggingInformationifyouwantthecompilertoadddebug informationtoyourcompile.ThisgeneratesaPDBfile(programdatabase)andinserts informationthatallowsyoutostepthroughcode,addbreakpoints,synchronizethe executionwiththesourcecodefiles,andsoon.

DebuggingBreakpointsMostofthetime,steppingthroughtheprograminitsentiretyisveryimpracticalbecause oftheprogram'ssize.Settingabreakpointsomewhereinthecodeallowstheprogramto runnormallyuntilthebreakpointisreached.Theprogramtemporarilyhaltswhenthe executioncomestothelineofcodewiththebreakpoint.Whenthishappens,theprogramisinwhat'scalledBreakmode.Thisallowsyoutoexaminethedata,checkthe logic,andsoon,andtheneithercontinueexecutionbypressingF5(orStart)again,or stepthroughthecode(F10orF11).Toinsertabreakpoint,placethecursorontheline ofcodewhereyouwanttobreaktheexecutionandpressF9.Youcanalsoclickonthe margintotheleftofyourcode.Abreakpointsymbolthendisplaysonthatlineasshown inFigure18 - 5 .

Figure18-5: Noticetheredcircularbreakpointsymbolontheleftmargin.

PartIV:DataAccessChapter21:IntroductiontoDataAccessin.NET Chapter22:ADO.NETChapter23:DataAccessinVisualStudio.NET Chapter24:IntroductiontoXMLin.NET

Chapter21:Introduction to Data Access in .NETVisualBasic3.0

Manyofthedeveloperswhowerefortunateenoughtobeusingversion2.0ofVisual BasictodevelopapplicationswouldagreethattheadoptionofVisualBasicbycorporate developersreallybeganin1993withthereleaseofVisualBasic3.0.Itwaswiththis releasethatMicrosoftfirstprovidedVisualBasicdeveloperswithamethodtoeasily connecttoavarietyofdatasourcesandbuildmuchmorerobust,data-driven applications.Withthisnewcapability,corporationscouldtakeadvantageofVisual Basic'sinherentrapidapplicationdevelopmentstrengthstoquicklybuildsolutionsthat utilizednewandexistingdatabasesthroughouttheirorganizations.WithVB3.0,thetwo primarytechnologiesthatmadethispossibleweretheJetdatabaseengineanda revolutionarynewobjectmodelcalledDataAccessObjects.

Jet databaseengineTheJetdatabaseenginewasinitiallydevelopedasthecoredatabaseenginebuiltinto theMicrosoftAccessdatabase,andalldevelopmentfromwithinAccessusedtheJet enginetointeractwiththeunderlyingdatabaseobjects.UntilthereleaseofVB3.0,this enginewasspecifictoAccess,anditsfeaturescouldnotbeusedfromanyother product.

DAOOneofthekeyreasonswhyVB3.0andthisearlyversionoftheJetEngine,version1.1, gainedsuchwidespreadacceptancewastheinclusionofanabstractobjectmodelfor interactingwiththeJetengine.Thisobjectmodel,calledDataAccessObjects(DAO), providedasimpleandflexiblemethodforconnectingtoandmanipulatingdatainany datasourcecompatiblewiththeJetengine.AlthoughtheuseofDAOswasstillsubject tothearchitecturallimitationsimposedbytheJetengine,thesimplicityofdataaccess throughtheDAOstructurealloweddeveloperstoquicklydeveloprobustandpowerful databaseapplicationsinVB.

VBSQLVisualBasic4.0includedsupportforaSQLServer-specificAPI,calledVBSQL,which providedVBdeveloperswithalow-levelAPIforconnectingdirectlytoaSQLServer database.ThisAPI,builtaroundtheC-BasedDB-Library,servedasalightweightand high-speedinterfacethatwasrelativelyeasytocodewhenusingVB.AlthoughVBSQL providedagreatsolutioninspecificsituations,thefactthatitcouldbeusedonlyto connecttoaSQLServerdatabase,whichdidn'thaveasignificantmarketshareinthe early'90s,severelyhindereditsacceptancebythedevelopmentcommunity.Also,as moreobject-orientedanddatabase-neutralmethodsfordatabaseaccessbecame available,developersbecamelesslikelytocodedirectlyinadatabase-specificAPI.

RDOAlsoincludedinVB4.0wasanewobjectmodelfordataaccesscalledRemoteData Objects,orRDO.TheinclusionofRDOwasanattempttoaddressanumberofdesign andscalabilityissuesthatdeveloperswerecurrentlyfacingwhendevelopinglarge distributedclient/serverapplicationswithDAOandJet.AlthoughtheuseofDAOandJet requiredaheavyamountofprocessingandmemorytobeutilizedontheclient,RDO providedamuchsmallerandfasterclient-sideobjectmodelwhileallowingtheRDMS systemtobearthebruntofalltheprocessing.Thistypeofarchitecturewasnotintended toreplacetheDAO/Jetdataaccessmethod,whichwasstillsuitableforAccessandotherISAMdatabases;insteadit,alloweddeveloperstotakeadvantageofthefeatures providedbymorepowerfulandfull-featureddatabasessuchasSQLServerandOracle.

OLEDB

DuetothewidespreadadoptionofMicrosoft'sActiveXDataObjects,orADO,the associatedincreaseinavailableOLEDBdrivershasgrownsignificantly.Thefollowingis ajustsmalllistofsomeofthemanydatasourcesthatcanbeaccessedthrougha providedOLEDBprovidertoday:

MicrosoftSQLServerdatabases Oracledatabases Jetdatabases MicrosoftOLAPservers ActiveDirectory MicrosoftExchangeWebFolders MicrosoftIndexServer Sybasedatabases Btrievedatabases AS/400(throughHostIntegrationServer2000) Textfiles SharepointPortalServerDocumentStorage(WSS)

VisualBasic6.0

BystandardizingonOLEDBprovidersasthecoretechnologyforinteractingwithany typeofrelationalornonrelationaldatastores,Microsoft'snextstepwastoprovide developerswiththenecessarydataconsumertobeusedbyamultitudeofclient applications.ThisnewconsumerwouldhavetobuildonthestandardOLEDBprovider conceptbyprovidingapowerfulyetsimpleobject-orientedinterfacetoanyOLEDB- exposeddatasource.

RecordsetsTheentiredevelopmentparadigmpresentedbyADO(andOLEDB)centersaroundthe Recordsetobject.TheRecordsetobjectservesasadeveloper'sprimaryinterface

whenusingADOtointeractwithadatabase,effectivelyservingasadeveloper'swindowintothedatastore.AllmanipulationoftheunderlyingdatausingADOoccursthroughthis window,andtheADOsubsystemitselfhandlesthedetailsofmakingsureallchangesaremadebacktothedatabase.Inessence,theRecordsetobjectallowsyouto programmaticallymanipulateasubsetofdatafromadatabasebyusingavarietyof differentobjects,techniques,andcursormodels.EachRecordsetexposesasetof rowsandcolumnsthatyoucantraversetogetorsettheinformationyouneed.Because ADOservestoexposethefunctionalityoftheunderlyingOLEDBproviders,the Recordsetobjectprovidesaconsistentandfamiliarinterfaceregardlessoftheoriginof aparticularsetofdata.OneofthekeydrawbacksintheimplementationoftheADORecordsetobjecthas beenthelackofasimplewaytoexposetheextendedtypesandfeaturesprovidedby anyindividualdatabaseorproductinastandardfashionfordeveloperstoworkwith. Becausemultipledatabasescanhavedifferentunderlyingdatastructuresforcommon datatypessuchasstringsanddates,theRecordsetobjectsimplymanipulatesall actualdatavaluesasVariantdatatypes.Thisallowsagreatamountofflexibilityand neutralitytotheRecordsetobjectwhendealingwithdiversedatasources,butithas alsoprovidedADOwithitssinglebiggestperformancehit.Byforcingeveryvalueof everyfieldinanADORecordsettobeaccessedasalateboundVariantdatatype,asignificantperformancelossisincurred.ThisisakeyfeaturethathasbeenaddressedintheimplementationofADO.NET.

Overview of ADO.NETWiththereleaseofADO.NETinthe.NETFramework,Microsofthasprovidednotonly anobjectmodelandinfrastructuretofacilitatedataaccess,butalsoacompletenew mindsetfordataaccessthatdiffersfromanythingpreviouslyavailable.Beforeyoubegin examiningthedetailsofusingtheADO.NETFrameworkinthenextchapte r ,itis importanttohaveanoverviewofthemajorpiecesofthe.NETdata-accessFramework tohelpprovideabigpictureofthearchitecturebehindthistechnology.

XML=data,data=XML

ThebasicprinciplebehindtheADO.NETimplementationliesinthefactthatalldatais representedinanXML-basedformat.Thisallowsvendorswishingtoprovideintegration withrelationaldatabasesornonrelationalstructurestosimplyimplementanewtypeof providerthatmanipulatestheirrespectivedatastoresintoXML,andhandlesmanipulatingthereturnedXMLbackintoaformatunderstandablebythedatastore.ThiscapabilitytoconsumeXMLasdataalsoallowsADO.NETunderstanddatafromanyXML-compliantapplicationorplatform.

ADO.NETstructureThebasicstructureoftheADO.NETobjectmodelrevolvesaroundtwoseparategroups ofobjects:DataSetsanddataproviders.DataSetsandtheirrelatedgroupsofobjects provideadatabase-neutralviewofanydatathatcanbeexposedasanXMLdocument. Thisstructureallowsdeveloperstomanipulateadisconnectedandhierarchicalviewof datainamannerthatshouldbeveryfamiliartoADOdevelopers.Appropriately,data providersserveasthelow-levelintegrationandmappingbetweenXMLdocuments,such asthosemanipulatedbyDataSets,andtheunderlyingdatabases.Dataproviders essentiallyserveasthe"bridge"betweenDataSetsanddatasources,whichallow DataSetstoessentiallyremainisolatedfromanyspecificdataimplementationorsource.Beyondthis"bridge"functionalitybetweendatabasesandDataSets,dataprovidersalsoservetoprovidealladditionaldatasource-specificfunctionalitysuchas datatypesandcommands.

DataSetsTheDataSetprovidesanobjectmodeltomanipulate oneormoretablesofdata.TheDataSetalsoprovidesthemeanstotrackandmaintain relationshipsbetweentables,andenforcesuchconstraintssuchasuniquevaluesand calculatedfields.

DataSetobjectmodelTherootoftheDataSetobjectmodelistheDataSetobjectitself,whichhandlesallthe baseservicesfortheentireunderlyingstructure,suchasserializingtoandfromXML.ItisthroughtheDataSetobjectthatdevelopersgainaccesstothemanyobjectsthat

worktogethertomakeuptheentireDataSetobjectmodel.Thefollowinglistgivesan overviewofeachofthekeyobjectsthatmakeuptheDataSetobjectmodel:

DataTable:ThisobjectrepresentsasingletableofdatawithinaDataSet.ADataSetmaycontainmultipleDataTableobjects, eachrepresentingalogicaltableofdata.

DataRow:EachDataTableobjectinaDataSetcontainsacollection ofzeroormoreDataRowobjectsrepresentingthedatawithinthat table.EachDataRowobjectservesasanarrayoffieldsthatare definedbytheDataColumncollectiondiscussedasfollows.

DataColumn:TheDataColumncollectionofaDataTablespecifiesinformationabouttheindividualcolumnsofdataineachtable.This schemainformationconsistsofalargenumberofpropertiesbeyond thestandardnameanddatatypeofaspecificcolumn.

DataRelation:TheDataRelationcollectionexistsdirectlyoffthe rootDataSetobject,andspecifiesinformationregardingthespecific tableandcolumnrelationshipsthatneedtobemaintainedbetween twoDataTableobjectsinasingleDataSet.

DataConstraint:ADataConstraintobjectprovidesameansfordeveloperstospecifyconstraintsthatmustbeenforcedona particularcolumninaDataTable.

Chapter22:ADO.NET

In This ChapterAccessingADO.NETfeaturesandnamespacesUsingADO.NETDataprovidersDataSets

Accessing ADO.NET Features and NamespacesBeforeyoucanstarttotakeadvantageofthefeaturesprovidedbyADO.NET,youmust knowhowtomakethesefeaturesavailablefromyourVB.NETapplications.BecausetheADO.NETobjectsareprovidedaspartofthebaseclassesofthe.NET Framework,theycanbemadeavailabletoaVisualBasic.NETprogrambyadding referencetotheSystem.Data.dllfromwithinyourapplication.Addingareferencetoanapplicationcanbedoneinavarietyofways,buttheeasiestisprobablytoright-clicktheResourcesfolderofyourprojectundertheSolutionExplorer window.Afterdoingthis,acontextmenuappears,inwhichyoumayselectAdd Reference.Fromthefollowingdialogbox,youmayaddthereferencetothe System.Data.dllbyselectingitfromthelistof.NETcomponents.

Table22-1:ADO.NETNamespaces

Namespace Description

System.Data Thisnamespacecontainsallmajorcomponents oftheDataSetobjectmodel.

System.Data.SqlTypes AcollectionofMicrosoftSQLServer-specific datatypes.

System.Data.SqlClient AMicrosoftSQLServer-specificdataprovider.

System.Data.OleDb AmanageddataprovideroptimizedforOleDBproviders.

System.Data.ODBC AmanageddataprovideroptimizedforODBCdrivers.

Using ADO.NET

Table22-2:ProviderInterfacesandObjects

Object BaseInterface

SQLServerProvider

OLEDBProvider

Connection IDBConnection SQLConnection OleDBConnection

Command IDBCommand SQLCommand OleDBCommand

DataReader IDataReader SQLDataReader OleDBDataReader

DataAdapter IDataAdapter SQLDataAdapter OleDBDataAdapter

Transaction IDBTransaction SQLTransaction OleDBTransaction

UnderstandingdataprovidersBeforeyougetintohowtomanipulateandchangedatathroughaDataSetobject,you shouldfocusontheobjectsthatmakeupadataprovider.Themajorityofthesamples providedinthischaptermakeuseoftheSQLServerprovider (System.Data.SqlClient). Althoughsomeoftheexamplesdemonstrateusingother providers,itisimportanttorealizethatalltheprovidersimplementthesamefunctionality andbasesetofobjects.Becauseeachdataprovidertargetsadifferenttypeofdataconnection,eachimplementsitsownsetofobjectsthatexposeastandardinterface.Also,itisimportanttonotethat eachproviderprovidesaseparatesetofobjects,eachhavingauniquename.Whatthis meansisthattheSQLproviderimplementsasetofobjectswithnamesprecededbya SQLprefix,andtheOleDBproviderimplementsasimilarsetofobjectsexposingthesameinterfaces,butwithnamesprecededbyanOleDBprefix.Thesesetsofobjectsarealsolocatedwithinuniquenamespaces.Thus,whenyouwishtotargetaSQLserver database,youcanusetheSQLproviderlocatedintheSystem.Data.SqlClient namespaceandcontainingobjectssuchasSqlCommandandSqlConnection.WhentargetingadatabasetowhichthereisonlyanexistingOleDBconnection,youcanuse theOleDBproviderthatislocatedintheSystem.Data.OleDBnamespace.Thesame objectsintheOleDBnamespacewouldbecalledOleDBCommandand OleDBConnection.

Table2 2 - 2 presentseachofthebaseADO.NETdataproviderinterfacesandtheir associatedimplementationforthetwomajorproviders:

ConnectionsWhendealingwithADO.NETdataproviders,theobviousstartingpointistheConnection object,whichprovidesthebasisforwhichalltheotherADO.NETdataproviderobjects acquireandmaintaintheirconnectionswiththeirassociateddatastores.Ifyouare familiarwithADOConnectionobjects,youshouldbeinstantlyfamiliarwiththe ConnectionobjectsimplementedinADO.NET.

'CreateaConnectionobjectsettingit'slocationinthe_

constructor

DimoConnectionAsNewSqlClient.SqlConnection("Data _

Source=(local);InitialCatalog=Northwind;Userid=sa")

'CreateanemptyConnectionobject

DimoConnection2AsNewSqlClient.SqlConnection()

'Setit'slocation

Connection2.ConnectionString ="DataSource=(local);Initial_

Catalog=Northwind;Userid=sa"

NoticethattheoConnectionandtheoConnection2objectsareidentical,butyou simplifytheconfigurationofthefirstonebyspecifyingtheconnectionstringwhenyou

instantiateyourinstanceoftheobject.Thistypeofoverrideisacommonoccurrencein the.NETFramework,andtakingadvantageofitcangreatlysimplifyyourcode.

CommandsNowthatyouhaveseenthesimplicityofconnectingtoadatasourcethroughthe Connectionobject,thechapterdiscussesCommandobjects.ADO.NETdataproviders useaCommandobjectwheneverdatasource-specificcommandsneedtobeexecuted againstaspecificdatasource.Themostcommontypesofcommandstobeexecuted againstadatasourceareSQLcommands,butthedataprovidermodelallowsfora separateCommandobjecttobeimplementedwheneverthisisn'tpossible.Inthefollowingexample,youcreateasimpleCommandobjecttoexecuteasingleSelectstatementagainstaserverbyusingtheSqlCommandimplementationprovided intheSystem.Data.SqlClientprovidernamespace.

'CreateanewcommandobjecttobeusedtoselectallCustomers

DimoCommandAsNew_

SqlClient.SqlCommand("Select *FromCustomers",oConnection)

DataReaderobjectsNowthatyouhavebecomefamiliarwithbothConnectionandCommandobjects,you takealookatthefirstoftwomajormethodsforviewingtheresultsofyourCommand queries.Thesetwomethods,DataSetsandDataReaders,providesolutionstotwo verydifferentproblemsforthedeveloper.Itisimportanttorealizethateachofthese objectsisthebestchoiceforcertainsituations,andneitherprovidesacatchallsolution (aswasthecasewiththeADORecordset).TheDataReaderobject,thefirstofthetwoyouexamine,isprovidedaspartofaspecificdataprovider.ThismeansthataSQLServer-specificimplementationofthe DataReader(SQLDataReader)exists,aswellasanOLEDB-specificimplementation (OleDBDataReader).Anyvendorimplementingasetofdataproviderobjectsofthe ADO.NETFrameworkfordataaccessprovidesanapplication-specificimplementationof theDataReaderinterface.

DataAdapterobjectsThenextandmostcomplexmajorcomponentofadataprovideristheDataAdapter object.DataAdapterobjectsprovidethemeansforadisconnectedDataSetobject, tointeractwithadatabase. DataAdapterobjectsprovidetheentiremappingfromthedatabaseintotheXMLformatunderstoodbytheDataSet;theyalsomaptheXMLreturnedbyaDataSetinto theappropriateInsert,Update,andDeleteCommandobjects,andsetallparameters accordingly.Thisallowsanydatabase-specificimplementationandSQLdetailstobe preconfiguredatdesigntimebythedeveloper,andabstractedintoaDataAdapter.

TableMappingsOneadditionalfeatureprovidedbytheDataAdapteristheabilitytoprovideasetof tableandcolumnmappingsthroughwhichitassociatesalltablenamesandcolumnnamesprovidedbytheDataSetagainstthoseactuallyusedbythedatastore.This allowsDataAdapterdeveloperstheabilitytoprovideaseparatesetofnamesfor tablesandcolumnstothefront-enddevelopersandusersoftheDataSetwhile maintainingallmappingsinaconsistentplace.

CreatingDataTablesThecoreoftheDataSetarchitectureiscenteredontheDataTableobject.Asingle DataSetcancontainmanyDataTableobjects,andaDataSetprovidesthecapability toenforcerelationshipsbetweenanytwoDataTables.TheTablescollectionofa DataSetcontainseachoftheDataTableswithintheDataSet.UsingtheTables collection,youcanaccessaspecificDataTablebyeitherusinganindexorthenameof thetable.ThestructureofeachDataTableisdefinedbyacollectionofDataColumnobjects.ThiscollectioncanbeaccesseddirectlyfromaDataTableobjectusingtheColumns property.EachDataColumnobjectexposesalargeamountofinformationdefiningthe structureofthatparticularcolumn.BymanipulatingaDataColumnobject,youcan configureexactlyhowacolumnofdatabehavesinaparticularDataTable.Thebasic

columnfeatures,suchasname,datatype,length,andinitialvalueareeasilyavailable, aswellasahostofmoreadvancedproperties.PropertiessuchasAutoNumber, ReadOnly,Caption,andUniqueprovideahostofpowerfulfeaturesthatyoucanuse tomakeaDataTablebehavemorelikeaclient-sidedatabase.Anotherhandyproperty of theDataColumnobjectistheColumnMappingproperty,whichallowsyoutocontrol howaspecificcolumnisaddedtotheunderlyingXML.TheavailableColumnMapping typesareElement,Attribute,Hidden,andSimpleContent.Thesesettingsaffect howaDataColumniswrittenoutwhenusingWriteXMLmethodofaDataSettowrite itscontentsoutasXML.

Chapter23:DataAccessinVisualStudio.NETIn This Chapter

AhistoryofMicrosoftdataaccesstechnologiesAnoverviewofADO.NET

Visual Studio .NET Database ToolsThefirstsetofVisualStudio.NETfeaturesprovidesyouwiththetoolstoeasily administerdatasources.Thesefeaturesallowyoutocreateandmanipulatedatabase objectssuchastables,views,andstoredprocedures.Also,developerscanusethese toolstoviewandeditthedatawithindatasourcestosimplifydebuggingandmonitoring ofdatabaseapplicationswithouthavingtouseaseparatetoolsuchasSQLServer EnterpriseManager.AlthoughthemajortoolsprovidedbyVisualStudio.NETareonly

brieflydiscussedinregardstodatabaseadministration,eachofthetoolsdiscussed providesagreatdealofpowertoyouwhenyoudevelopdatabaseapplicationsfrom VisualStudio.NET.

UsingServerExplorerTheVisualStudio.NETServerExplorerwindowservesasadeveloper'swindowintonot onlydatabaseobjects,butalsoamyriadofotherservicesthatcanbeaccessedon remotemachines.TheServerExplorerwindow,likesomanyothertoolsinVisualStudio.NET,canbedockedandmadeeasilyavailableduringregulardevelopment(seeFigure23 - 1 ).

Figure23-1: YouusetheVisualStudio.NETServerExplorertomanipulateDatabaseObjectsandremoterServersdirectlyfromtheVisualStudio.NETIDE.

ThenodesintheServerExplorerwindowarepresentedintwoseparatesections:DataConnectionsandServers:

TheDataConnectionssectionletsyouaddconnectionstoregularlyused dataconnections.Afterthesedataconnectionsareestablished,the ServerExplorerwindowenablesyoutomanipulatetheunderlying databaseobjects.

TheServerssectionallowsyoutoconnecttoremoteservers,andprogramagainstavarietyofservicesthatmaybeavailable,suchasWeb services.

AddingconnectionsToaddaconnectiontotheServerExplorer,right-clickthenodeandselectAdd Connectionfromthepop-upmenu.AfterclickingAddConnection,theDataLink Propertiesdialogbox,whichprovidesalltheoptionsavailableforaddingavaliddata connectionusingavarietyofavailabledriversanddatasources,opens.Asyouseelater inthechapter,byhavingthisconnectionavailableintheServerExplorer,youcaneasily dragtheconnectionsontoformsorcomponents;VisualStudio.NETandtheIDE automaticallyaddtheappropriatecodetoconfiguretheconnectionwithinthatitemofa

project.Figure2 3 - 2 illustratessomeoftheoptionsavailablewhenconfiguringanew dataconnection:

Figure23-2: YouusetheDataLinkPropertiesdialogboxtoaddconnectionstotheServerExplorer.

ToproperlyconfigureadatabaseconnectioninVisualStudio.NETbyusingtheData LinkPropertiesdialogbox,youmustselecttheappropriateproviderandconnection information,suchasservername,databasename,andlogincredentials.Afterthese settingshavebeenproperlyconfigured,youcanaccessthisconnectioninformation,and manipulatedatabaseobjectsunderneaththisconnectionifthedatasourcesupportsthis, regardlessoftheVisualStudio.NETsolutionthatiscurrentlyopen.Thisfeatureallows youtoaddconnectionstoyourmostcommonlyuseddatabasesand,ifrequired,easily sharethemacrosssolutionswithouthavingtoreconnectorconfigure.

AdministeringdatasourcesthroughtheServerExplorer

OneofthebesttimesavingfeaturesavailablefromwithinVisualStudio.NETisthe capabilitytocompletelyadministermostdatasourceswithoutleavingtheIDE.This administration,similartothatprovidedbySQLServerEnterpriseManager,allowsyouto addandconfiguredatabasediagrams,tables,views,andstoredprocedures.

ManipulatingdatabasetablesinVisualStudio.NETByusingtheServerExplorerwindowtoexpandaspecificdatabaseconnection,youcan navigatetotheTablesnodetogainaccesstoalistofallexistingusertablesinthe database.Byright-clickingtheTablesnode,youcanselecttheNewTableoptionfrom theresultingpop-upmenutoaddanewtabletothedatabase.Also,byright-clickingan existingtableandselectingtheDesignTableoption,youcanmodifythestructureof existingdatatables.Figure23 - 3displaysthetabledesignerusedbyVisualStudio.NET tomanipulatedatabasetablestructures.

Figure23-3: TheVisualStudio.NETdatabasetabledesignerallowsyoutomanipulatethe structureofdatabasetablesfromdirectlywithintheIDE.

ThetabledesignerprovidedbyVisualStudio.NETallowsyoutomodifythestructureof tablesbyprovidingcompletecontroloveratable'scolumninformation.Asshownin Figure23 - 3,thecolumninformationforatablecanbeeasilyeditedinthegridprovided bythetabledesigner.Otherfeaturesavailablefromwithinthetabledesignerthatcanbe accessedfromtheVisualStudio.NETtoolbarwhenthetabledesignerisopeninclude theabilitytomodifycolumnindexesandforeignkeyrelationships.

Beyondtheabilitytodesigntables,theServerExplorerwindowprovidesyouwiththe abilitytoviewthedatainatable,exportallthedatatoafile,generatetheappropriate SQLscripttore-createthetableonanotherdatabase,andaddatriggertothe database—allfromwithinthestandarddevelopmentenvironment.Eachofthese functionsisavailablebyright-clickingtheappropriatetablenodeintheServerExplorer window.

ManipulatingdatabaseviewsinVisualStudio.NETWhenworkingwithdatabaseviews,VisualStudio.NETutilizesafull-featured,built-in queryanalyzer.ThisqueryanalyzerallowsyoutoconstructoreditSQLstatementsina mannerverysimilartousingthequeryanalyzerinSQLServerEnterpriseManager.You spendmoretimeonthequeryanalyzerinthefollowingsectionthatdiscussesstored procedures.Inadditiontothequeryanalyzer,VisualStudio.NETprovidesyouwitha powerfulquerybuilderforgraphicallydesigningandconstructingSQLstatementsand views.TheVisualStudio.NETquerybuildergivesyoutheoptionofbuildingthequeries graphicallyorbymanuallykeyingtherequiredSQLstatements.Also,byutilizingthe querybuilder,youcanverifythevalidityoftheSQLstatementsagainsttheappropriate datastore,andevenexecutethestatementandpreviewtheresults,asshowninFigure23 - 4 .

Figure23-4: TheVisualStudio.NETquerybuilderprovidesyouwithanumberoftoolsto graphicallyconstructSQLqueriesandviews.

Thequerybuilderitselfisbrokenintofourverticallypositionedpanes(asshowninFigure23 - 4 ).Thefollowinglistprovidesabriefdescriptionofeach ofthesepanesfromtopto bottom:

DiagramPane—Providesagraphicalrepresentationofthetables includedinaSQLstatementandthejoinsbetweenthem.Byaddingor removingtablesfromthispane,thequerybuilderautomaticallymakes theappropriateadjustmentstotheSQLpane(describedbelow).Also, bycheckingtheboxnexttoanycolumninanytable,youcanchoosetoincludethatparticularcolumnintheresultingquery.

GridPane—Providesyouwiththeabilitytoseeallthecolumns selectedtobereturnedasaresultofexecutingthecurrentquery.This panealsoprovidesyouwiththeabilitytoentercriteriaandfiltersbasedonaspecificcolumn,andtospecifyacolumnaliasandsorting information.

SQLPane—ThispaneinthequerybuilderdisplaysthecurrentSQL statementasdefinedbyyourmodificationstotheDiagramandGrid panes.YoualsohavetheabilitytomakechangesdirectlytotheSQL paneandseethemreflectedintheabovetwopanes.

ResultsPane—Itisinthispanethatyoucanviewtheresultsofa queryexecutedafterclickingtheRunbuttononthetoolbar.

Asyoucansee,thequerybuilderprovidesanumberoffeaturestogreatlysimplifythe generationofSQLstatements.Andasdiscussedinthenextsectio n onmanipulating storedprocedures,thequerybuilderintegratestightlywiththequeryanalyzerinVisual Studio.NETtoallowyoutoquicklybuildverycomplexstoredproceduresmadeupofa numberoflogical"blocks"ofSQLstatements.

PartV:WindowsFormsChapter25:IntroductiontoSystem.Windows.FormsChapter26:ControlsChapter27:SpecificControls Chapter28:"Visual"Inheritance Chapter29:IrregularFormsChapter30:OtherNamespacesandObjectsintheCatalog

Chapter25:IntroductiontoSystem. Windows.FormsWhatconstitutesawindow?

Awindow,initscrudestform,isanenclosed,rectangularareaofthescreen.Itis typicallydefinedbyaboundingrectangle(visibleornot)andoftencontainsdataorother windows.Bythisdefinition,notonlyareformswindows,butcontrolsarewindowsas well.

IntheWindowsoperatingsystem,ahandleidentifiesawindow.Thisisanalogoustoan onlinehandle,oraCBhandle.Inthecaseofwindowsprogramming,thehandleis uniqueamongstallwindowscurrentlyloaded.Furthermore,awindowhandleremains constantuntilthewindowisunloaded.

VisualBasic4introducedatypeofcontrolcalledlightweightorwindowless.Thesewerecontrols(forexample,theLineandShapecontrols)thatdidnothaveabounding rectangleorahandle.Theyessentiallyconstitutedasetofinstructionsforthecontainer controltopaint.Theintroductionofthesecontrolsledtomanyinconsistenciesforthedeveloperbecause windowedandwindowlesscontrolshadtobehandleddifferently.Furthermore,these controlshadsignificantlyreducedfunctionalityduetotheirlackofahandle.

In.NET,everycontrolis"windowed,"whichhasadvantagesanddisadvantages.The goodsideisthatyounowhaveathoroughlyconsistentframeworkuponwhichto develop.Allcontrolshaveahandleandcanreceiveanyrelevantornecessarymessage. Thedownsideisthatsomecontrolsthatmaynotneedtoreceivemessagesorbe identifiedbyWindowsnowhavetheoverheadofawindow.Inshort,thismeansthatcontrolssuchastheLineandShapecontrols,whicharenolongerpresentwithin.NET,canbeaccomplishedonlybyexplicitlycomposingthe paintingcode.Which,inmyopinion,isexactlythewaytheyneedtobe.

Whatcanawindowdo?

Awindowistheprimarymethodofinteractionbetweenyoursoftwareandtheenduser. Thus,ithandlesalltheinput(keyboard,mouse,andsoon)fromtheuser,andprocesses itaccordingtoyourinstructions.Furthermore,itdisplaysanyinformationyouinstructitto withanyformattingyoudesire.

Thefactthatthe.NETFrameworkhasnowmadeitemssuchasformsandcontrolsfully inheritableclassesalmostremovesallneedtoprogramagainsttheWin32API.Asa developer,youcannowgettheentirewindowprocessingpowerforfreeinwhateveryou wishtoaccomplish.ItisstillpossibletodealwiththeWin32APIdirectly,though.Methodsincludecalling P/InvokeoroverridingtheWndProcfunction.Thisabilityiscrucialforaccomplishing certaintasksthathavenotyetbeenimplementedintheframework.However,youwill findthatyourusageofthesemethodswillbeminimal.

Basics of the Windows FormTheWindowsForm(seeFigure25 - 1 )isessentially,themostimportantcontrolinyour repertoireasaGUI(GraphicalUserInterface)developer.TheFormisthecanvasupon whichyoupaintthecontrolsrequiredfortheenduserstoaccomplishtheirgoalsofdata entry,systemadministration,softwaredevelopment,oranynumberofinfinitetasks.

Figure25-1: Theever-importanttabularasa.

TheFormisacontrollikeanyotherinthetoolbox,yetitissomuchmore.Youlearnwhy throughoutthesechapters.

WheredoestheWindowsFormcomefrom?ThehierarchyofobjectsfromwhichtheWindowsFormisderivedisshowninFigure 25 - 2.

Figure25-2: TheWindowsFormclassancestry.Top 10 Reasons Why a Windows Form Is Better than a VisualBasic 6 FormThefollowinglistdelineates10itemsthatwerepreviouslyunavailableorunacceptablein VisualBasic6thathavebeenrectifiedinVisualBasic.NET.Opinionsdifferonthe"best" changesthathaveoccurred.Hopefully,though,thislistaddressesthemajorityofthe opinions.

10.AWindowsFormhastwiceasmanypropertiesandmethodsasanoldform.TheWindowsFormexposessignificantlymoreproperties, methods,andeventsthantheVisualBasic6 form.Thismeansmore functionalityisavailableforyoutoplaywith.Plus,thereisareduced levelofdependencyontheWin32API.Overall,theadditionofproperties,methodsandeventsfurtherenhancestherapiddevelopment experiencebyexposingsignificantlymorebehavior.9. AWindowsFormcaneasilycontainadockabletoolbar.The

WindowsFormsframeworkintroduceshandyconceptssuchasdocking, whichareeasilygraspedandimplementedbythenovicedeveloper. DockablewindowsinVisualBasic6werevirtuallyimpossibletoimplement.ThishandyfeaturecanbeeasilyleveragedtocreatericherGUIsthaneverbefore.

8. WindowsFormsareopaqueuntilthey'renot.TheWindowsForms frameworkintroducesapropertycalledopacity.Thisisnotaparticularly newconceptbecauseVisualBasicformshavealwaysbeenopaque. However,ratherthanusetheSetLayeredWindowsAttributesAPI onalayeredwindowtocreatevaryinglevelsoftranslucency,this propertyallowsyoutocreateatranslucentwindowbysettingaproperty. (CheckouttheSearchWindowinTextPadforagooduseofthis concept.)Thisconceptcanbeparticularlyusefulinthedevelopmentof moregraphicallyorientedapplications.

7.

Youcancapturethemousewheelwiththegreatestofease.Itmaybealittlething,butdarnit,you'llbehappyaboutit.InVisualBasic.NET, whenacontrolhasthefocusandtheuserscrollsthemousewheel,you canrespond,ifnecessary.ThiswasanothertaskfortheAPIinVisual Basic6.InMicrosoftExcel,holdingdowntheCTRLkeyandscrollingthe mousewheelresultsintheZoomFactorchanging.Thistypeof functionalitycanbeveryeasilyimplementedwiththeinclusionofa mousewheelevent.6. Thereisnowanobject-orientedapproachforgraphics. EverywindowinVisualBasic.NEThasanassociatedGraphicsObject.Every forminVisualBasic6hasaDeviceContext.InVisualBasic6,you neededtheDeviceContexttopasstotheAPIcallsnecessarytodrawa polygon.InWindowsForms,youcancalltheDrawPolygonmethodof theGraphicsObject.5. Allborderstylesareavailabletoyouatanytimeviathe

FormBorderStyleproperty.InVisualBasic6,youwereprevented fromeasilychangingtheborderofaformtocertainvalues.Youwere requiredtodestroytheformandthenredisplayit.VisualBasic.NETnow handlesallofthisforyou.Youmayrunintoproblemsregardingchanging handles,asoutlinedinthepitfallssectionofthischapter,buthowoftendoyouneedthehandleinWindowsForms?

4. AutoscrollisnotjustGermanparchment.AWindowsFormnow supportsautoscrolling.Autoscrollingsimplymeansthatthescrollbars appearonaformifanyofthecontrolsresideoutsidethevisibleareaof theform.Thisisaveryhandyfeaturefordealingwithsignificant variationsinresolution.InVisualBasic6,youhadtodevelopforthe lowestcommondenominator,600x480.

3.

AWindowsFormcananchorlikeasailor.Manyimportantpartsofthegraphicaluserinterfacedesigninvolvethelittlethings—thedetailsthat maketheenduser'sexperienceworthwhile.Onetheselittlethingsis resizeablewindows.VisualBasic6alwayshadresizeablewindows,but howdoyoumovethecontrolsinaccordancewiththeform?Theonly waytohandlethisinthepastwaswithafairamountofcodethat analyzedpositionsandratios,andmovedthecontrolstotheappropriate place.WindowsFormsintroducesaconceptcalledanchoring,which groundsthecontrolsintheirrespectivepositionsinrelationtotheir container.Nothingcouldbeeasier.2.

Youdon'tneednostinkingtwips.FewthingsweremorecumbersomeinVisualBasic6thanunitsofmeasurement.Okay,somethingswere morecumbersome,butthisonereallybuggedme.InWindowsForms, everythingismeasuredinpixels.Thismakesforveryconsistentinterface development.1.

IntheWindowsFormsframework,aformisjustaclass.ThemysticalVisualBasic6formisgone;ithasbeenreplacedbyafully extensibleandinheritableclasswithvisualcapabilities.Oneofthemost valuableresultsofthisisVisualInheritance.Thisfeatureisfully addressedin Chapter28 .

Chapter26:Controls

System.Windows.Forms.Control

Table26-1:PublicSharedPropertiesoftheControl

PropertyName DescriptionDefaultBackColor Read-only.Returnswhatthebackgroundcolorof

thecontrolwouldbeifthebackgroundcolorwere notexplicitlyset.

DefaultFont Read-only.Returnswhatthefontofthecontrol wouldbeifthefontwerenotexplicitlyset.

DefaultForeColor Read-only.Returnswhatthe foregroundcolorof thecontrolwouldbeif theforegroundcolorwere notexplicitlyset.

ModifierKeys Read-only.Returnsabitwisecombinationof valuesgivingthecurrentstateoftheCtrl,Alt,and Shiftkeys.

MouseButtons Read-only.Returnsabitwisecombinationof valuesgivingthecurrentstateoftheleft,middle, andrightmousebuttons.

MousePosition** Read-only.Returnsapointgivingthecurrent positionofthemouserelevanttotheupper-left cornerofthewindow.

PublicinstancepropertiesApublicinstancepropertyrequiresthattheclassbeinstantiated.Thepropertyvalues arenotsharedwithanyotherinstances.Thus,iftwoinstancesofanobjectarecreated, thevalueofonepropertyofthefirstinstanceisnotguaranteedtobethesameasthe valueofthesamepropertyofthesecondinstance.Table26-2:PublicInstancePropertiesoftheControl

PropertyName DescriptionAccessibilityObject SpecifiestheAccessibleObject

assignedtothecontrol.An AccessibleObjectisusedbyan accessabilityapplicationthataccomodates foruserswithdisabilities.

Table26-2:PublicInstancePropertiesoftheControl

PropertyName DescriptionAccessibleDefaultActionDescription Specifiesthedescriptionofthedefault

actionofthecontrolwhenaccessedbyan accessiblityapplication.

AccessibleDescription Specifiesthedescriptionofthecontrol whenusedinthecontextofanaccessibity application.

AccessibleName Specifiesthenameofthecontrolinthe contextofanaccessibilityapplication.

AccessibleRole Specifiestheroleofthecontrolinthe contextofanaccessibilityapplication.The resultisavalueintheAccessibleRole enumeration;forexample,scrollbarand pushbutton.

AllowDrop Specifieswhetherthecontrolacceptsdata thatisdraggedanddroppedintoitbythe user.

Anchor Specifieswhichedgesofthecontrolare boundtotheedgesofitscontainer.

BackColor Specifiesthebackgroundcolorofthe control.

BackGroundImage Specifiesthebackgroundimageofthe control.

BindingContext Specifiesthebindingcontextofthecontrol. ThismanagestheBindingManagerBase Collectionforthecontrol.Each BindingManagerBasecontrolsbindingto onedatasource.So,ifyouhavethreetext boxes,eachboundtoadifferentcolumnin thesametable,theBindingManagerBaseguaranteessynchronization.

Bottom Read-only.Returnsthey-coordinateofthe bottomedgeofthecontrolrelativetothe control'scontainerclientarea.

Bounds Specifiestheboundingrectangleforthe control.

CanFocus Read-only.Returnswhetherthecontrolcan receivethefocus.

CanSelect Read-only.Returnswhetherthecontrolcan beselected.

Capture Specifieswhetherthecontrolhascaptured themouse.Capture=Truemeansthat thecontrolreceivesallthemouse messages,regardlessofthepointerbeing intheclientareaofthecontrol.

CausesValidation** Specifieswhetherall controlsrequiring validationreceivesit whenthiscontrol receivesthefocus.


PropertyName DescriptionClientRectangle Read-only.Returnstheclientareaofthe

control.Controlswithnon-clientregions, suchasthetitlebaronaform,donot includetheseregionsinthisrectangle.

ClientSize Read-only.Returnstheheightandwidthof theclientareaofthecontrol.

CompanyName Read-only.Returnsthecompanynameof theapplicationcontainingthecontrol.

ContainsFocus Read-only.Returnswhetherthecontrolor oneofitschildcontrolscurrentlyhasthe inputfocus.

ContextMenu Specifiesthecontextmenuobject(a.k.a. right-clickmenu)associatedwiththis control.

Controls Specifiesthecollectionofcontrolscurrently containedwithinthecontrol.*

Created Read-only.Returnswhetherthecontrolhas beencreated.Nottobeconfusedwith IsHandleCreated.

Cursor Specifiesthecursorthatisdisplayedwhen themousepointermovesoverthecontrol. Forexample,Cursors.WaitCursor changesthecursortoanhourglass.

DataBindings Read-only.Returnsthecollectionofsimple bindingobjectsforthecontrol.

DisplayRectangle Read-only.Alsoreturnstheclientrectangle ofthecontrol.However,inheritedcontrols maywishtomodifythis.

Disposing Read-only.Returnswhetherthecontrolis currentlyintheprocessofbeingdisposed. Note:Whenacontrolisdisposed,itisno longeraccessibleasavalidinstance. However,itmayremaininmemoryuntilthe garbagecollectorreclaimsit.

Dock Specifiestowhichedgeofthecontainerthe controlisdocked.Whenspecified,the resizingofthecontrolishandled automatically.Controlsthatare"dockable" requirecodeanalyzingwindowmovements coupledwiththesettingofthisproperty.

Enabled Specifieswhetherthecontrolis enabled. Thisalsocoversitemssuchas receiving focus.

Focused Readonly.Returnswhetherthecontrol currentlyhastheinputfocus.

Font Specifiesthecurrentfontforthecontrol.ForeColor Specifiestheforegroundcolorofthe


PropertyName Descriptioncontrol.

Handle Read-only.ReturnstheWindowhandlefor thecontrol.

HasChildren Read-only.Returnswhetherthecontrol containschildren.*

Height Specifiesthefullheightofthecontrol.IMEMode SpecifiestheInputMethodEditormode

supportedbythiscontrol.TheIMEisused forallowinguserstoentercharacters neededforAsianlanguages.

InvokeRequired Readonly.ReturnswhetherInvokemust beusedwhenmakingmethodcallsonthis control.Typically,trueonlywhenthehandle ofthecontrolisonadifferentthreadthanthemethodcall.

IsAccessible Specifieswhetherthecontrolisvisibleto accessiblityapplications.

IsDisposed Read-only.Returnswhetherthecontrolhas beendisposed.Iftrue,thecontrolisno longeraccessibleasavalidreference.

IsHandleCreated Read-only.Returnswhetherawindow handlehasbeenassociatedwiththis control.

Left Specifiesthex-coordinateoftheleftedge ofthecontrol'swindow.

Location Specifiesthecoordinatesoftheupper-left cornerofthecontrolrelativetotheupper- leftcornerofthecontrol'scontainer.

Name Specifiesthenameofthecontrol.Thisvalueistypicallyusedtorefertothecontrol incode.

Parent Specifiestheparentcontainerofthe control.

ProductName Read-only.Returnstheproductnameofthe applicationcontainingthecontrol.

ProductVersion Read-only.Returnstheversionnumberof theapplicationcontainingthecontrol.

RecreatingHandle Read-only.Returnswhetherthehandleof thecontroliscurrentlybeingre-created. Thecomboboxsampleintheprevious chapte r demonstratedhowthiscanoccur.Region Specifiestheellipticalorpolygonalarea withinthewindowassociatedwiththis control.Youseemanyexamplesofthis propertyinthechapteronirregularforms.

Right Read-only.Returnsthex-coordinateforthe


PropertyName Descriptionrightedgeofthecontrolrelativetothe containercontrol'sclientarea.

RightToLeft Specifieswhetherthealignmentofthe control'selementsisright-to-left.This propertyisusedtosupportlocaleswith right-to-leftfonts.

Size Specifiestheheightandwidthofthefull control.

TabIndex Specifiesthiscontrol'splaceinthetab orderofallcontrolswithinthesame container.

TabStop Specifieswhetherthecontrolcanreceive focusviatheTabkey.

Tag Specifiesextraneousdataforthecontrol. Forexample,ifacontrolneedsareference toaspecificobjectforittosuitthe programmer'sneeds,thispropertycould housethatobject.

Text Specifiesthe text associatedwiththis control.Thisis typically,althoughnot always,thetextdisplayed.

Top Specifiesthey-coordinateofthetopedge ofthecontrolrelativetothecontrol's containerclientarea.

TopLevelControl Read-only.Returnsthetop-levelcontrol thatcontainsthecurrentcontrol.Inthe instanceofaformcontainingmany containercontrolsthatinturncontainmay othercontrols,theformisreturnedforall controls.

Visible Specifieswhetherthecontrolisvisible.Width Specifiesthefullwidthofthecontrol.*Thesepropertiesmakereferencetocontainmentbythiscontrol;basedonthe hierarchy,onewouldconcludethatthisfunctionalityisincorrect.Table26 - 4coversthisinmoredetail.

EventsTheControlisalsotheprimarysourceofmanyoftheeventsavailabletoyouviaother controls.Table26 - 1 0 givesanorganizedsynopsiswithenhanceddescriptionsofthe eventsthatcomefromtheControlobject.Notethatmanyoftheeventsareveryself- explanatory.Specificexamplesforeventsinthefollowingtablearenotprovided.Other samplesthroughoutthischapteruseeventsextensively,andshouldgiveanindicationas towhattheydo.Table26-10:PublicInstanceEventsoftheControl

EventName DescriptionBackColorChanged Occurswhenthe BackColor propertyofthe controlchanges.

BackgroundImageChanged Occurswhenthe BackgroundIma geofthecontrol changes.

BindingContextChanged Occurswhenthe BindingContex tpropertyofthe controlchanges.

CausesValidationChanged Occurswhenthe CausesValidat ionproperty changes.

ChangeUICues Occurswhen Focusor Keyboardcues change.

Click Occurswhen the control has been clicked.ContextMenuChanged Occurswhenthe ContextMenu propertyofthe controlchanges.

ControlAdded Occurswhena controlhasbeen addedtothis control.

ControlRemoved Occurswhena controlhasbeen removedfromthis control.

CursorChanged Occurswhenthe Cursorproperty ofthiscontrol changes.

Disposed(InheritedfromComponent)

Representsthe methodthat handlesthe Disposedevent ofacomponent. Occurswhenthecomponent's resourcesare freed.

Table26-10:PublicInstanceEventsoftheControl

EventName Description

DockChanged Occurswhenthe Dockpropertyof thecontrol changes.

DoubleClick Occurswhen the controlhas been double-clicked.

DragDrop Occurswhena drag-and-drop operationhas beencompleted.DragEnter Occurswhenan objecthasbeen draggedtobe withinthe control'sbounds.

DragLeave Occurswhenan objecthasbeen draggedoutofthe control'sbounds.

DragOver Occurswhenan objecthasbeen draggedovera control'sbounds. Thiseventcovers theDragEnter andDragLeave events.

EnabledChanged Occurswhenthe Enabledproperty ofthiscontrol changes.

Enter Occurswhenthe controlisentered.

FontChanged Occurswhenthe Fontpropertyof thiscontrol changes.

ForeColorChanged Occurswhenthe ForeColor propertyofthe controlchanges.

GiveFeedback Occursduringa dragoperation. Thisistheevent thatallowsthe applicationto changethemousecursorand soon.


EventName Description

GotFocus Occurswhenthe controlreceives thefocus.

HandleCreated Occurswhenthe handleforthe windowis created.

HandleDestroyed Occurswhenthe handleforthe windowis destroyed.HelpRequested Occurswhenhelp isrequestedfora control.For example,by pressingF1.

IMEModeChanged Occurswhenthe IMEModeproperty changes.Invalidated Occurswhenthe control'sdisplayis updated.The rectanglethatis

invalidisavailableviathisevent.KeyDown Occurswhen a keyis pressed down while the controlhas the focus.

KeyPress Occurswhena keyispressed whilethecontrol hasthefocus.KeyUp Occurswhena keyisreleased whilethecontrol hasthefocus.

Layout Occurswhena controllaysoutits childcontrols.

Leave Occurswhenthe controlisleft.

LocationChanged Occurswhenthe Location propertyofa controlchanges.


EventName DescriptionLostFocus Occurswhenthe controlloses focus.

MouseDown Occurswhena mousebuttonis pressedwhilethe pointerisovera control.

MouseEnter Occurswhenthe mousepointer entersthecontrol.MouseHover Occurswhenthe mousepointer hoversovera control.

MouseLeave Occurswhenthe mousepointer leavesthecontrol.

MouseMove Occurswhenthe mousepointer moveswithinthe control.MouseUp Occurswhena mousebuttonis releasedwhilethe mousepointeris

overacontrol.MouseWheel Occurswhenthe mousewheel moveswhenthe controlhasthe focus.

Move Occurswhenthe controlismoved.

Paint Occurswhenthe controlisdrawn orredrawn.

ParentChanged Occurswhenthe valueofthe Parentproperty ofacontrolhas changed.

QueryAccessibilityHelp

Occurswhenthe Accessible objectofthe controlis providinghelpto accessibility applications.

Table27-1:Non-InheritedMembersofButtonBase

MemberName(scopeandtype) DescriptionFlatStyle(PublicInstanceProperty) Specfiesthe FlatStyle of the control.Can

beoneof fourvalues: Flat, PopUp, Standard, orSystem.

Image(PublicInstanceProperty) Specifesthe imagethat isdisplayed onthe Button control.

ImageAlign(PublicInstanceProperty) Specifies the alignmentof theimage displayedontheButton control.

ImageIndex(PublicInstanceProperty) SpecifiestheIndex valueofthe imageinthe imagelist displayedon theButton control.See ImageList

Table27-2:Non-InheritedMembersofListControl

MemberName(scopeandtype) DescriptionDataSource(PublicInstanceProperty) Specifiesthe DataSource ofalistcontrol. Thisistypically

acollectionor array.DisplayMember(PublicInstanceProperty) Ifthelist control contains objectsthat support

properties,this indicateswhich

Chapter27:SpecificControlsThereareafewcontrolsthatarebeyondthescopeofthis chaptersuchastheCrystalReportViewerandtheActiveXHostcontrols.

ButtonBaseThepurposeoftheButtonBasecontrolistoprovideallthebasicfunctionalitythatany buttonstylecontrolrequires.Thisclassinheritsdirectlyfromcontrol.Table2 7 - 1 listsand describestheproperties,methods,andeventsthatButtonBasebringstothetable.

ListControlThepurposeoftheListControlistoprovideallofthebasicfunctionalitythatanylist stylecontrolrequires.ThisclassinheritsdirectlyfromControl.Table2 7 - 2 listsand describestheproperties,methods,andeventsthattheListControlbringstothe table.

Table27-2:Non-InheritedMembersofListControl

MemberName(scopeandtype) Descriptionpropertyofthe objectto display.If unspecified,theresultoftheToString methodis used.SelectedIndex(PublicInstanceProperty) Specifiesthe indexofthe selecteditemin the ListControl.

SelectedValue(PublicInstanceProperty) Specifiesthe objectselected inthe ListControl.

ValueMember(PublicInstanceProperty) Analogousto DisplayMemb er.This indicateswhich propertyofthe objecttoreturn.

GetItemText(PublicInstanceMethod) Similartoa ToString Method.This method, however,takes anobjectasa parameterand returnsthetext ofthatobject.

DataSourceChanged(PublicInstanceEvent) Occurswhen the DataSource property changes.

DisplayMemberChanged(PublicInstanceEvent) Occurswhen the DisplayMemb erproperty changes.

SelectedValueChanged(PublicInstanceEvent) Occurswhen the SelectedVal uechanges.

Table27-3:Non-InheritedMembersofScrollableControl

MemberName(scopeandtype) DescriptionAutoScroll(PublicInstanceProperty) Specifieswhether ornotthe containerallows

theusertoscroll toanyitems beyondthevisible boundaries. Settingthisto trueessentially createsavirtual spacegreater thanthevisible space.

AutoScrollMargin(PublicInstanceProperty) Specifiesthe distancefromthe edgeofthe containerthata controlmustbe forthescrollbars toappear.

ValueMemberChanged(PublicInstanceEvent) Occurswhen the ValueMember property changes.

DataManager(ProtectedInstanceProperty) Handles managementof theBindingCont extofthe ListControl

ScrollableControlThepurposeoftheScrollableControlistoprovideallthebasicfunctionalitythat anyscrollingcontrolrequires,specificallyAutoScroll.Thisclassinheritsdirectlyfrom Control.Table27 - 3listsanddescribestheproperties,methods,andeventsthatthe ScrollableControlbringstothetable.

MenuThepurposeoftheMenuclassistoprovideallofthebasicfunctionalityformenus.This classinheritsdirectlyfromComponent. Table2 7 - 4 listsanddescribestheproperties, methods,andeventsthattheMenubringstothetable.

Table27-4:Non-InheritedMembersoftheMenuClass

MemberName(scopeandtype) DescriptionHandle(PublicInstanceProperty) ReadOnly. Returnsthe handlethat represents thewindow ofthis

object.

IsParent(PublicInstanceProperty) ReadOnly. Returnsa value indicating whetheror notthis menucontainsany menuitems.

MDIListItem(PublicInstanceProperty) ReadOnly. Returnsa value indicating themenu itemthatis usedtodisplayalistofMDIchild forms.

MenuItems(PublicInstanceProperty) ReadOnly. Returnsa collectionof menuitems associated withthis menu.

GetContextMenu(PublicInstanceMethod)

Returnsthe ContextMenuobject thatcontainsthismenu.

GetMainMenu(PublicInstanceMethod) Returnsthe MainMenu objectthat containsthis menu.

MergeMenu(PublicInstanceMethod) Mergesthe menuitem collections oftwo menus.

CloneMenu(ProtectedInstanceMethod) Performsa deep-copy of the current

ScrollBarThepurposeoftheScrollBarclassistoprovideallthebasicfunctionalitythatany scrollbarcontrolrequires.ThisclassinheritsdirectlyfromControl.Table2 7 - 5 listsand describestheproperties,methods,andeventsthattheScrollBarclassbringstothe table.Table27-5:Non-InheritedMembersoftheScrollBarClass

MemberName(scopeandtype) DescriptionLargeChange(PublicInstanceProperty) Specifiesthe valuetoaddor subtractfrom thevalue

propertywhen thescrollboxis movedagreat distance.

Maximum(PublicInstanceProperty) Specifies the upperlimit of the scrollbar value.

Minimum(PublicInstanceProperty) Specifies the lowerlimit of the scrollbar value.

SmallChange(PublicInstanceProperty) Specifiesthe valuetoaddor subtractfrom thevalue propertywhen thescrollboxis movedasmall distance.

Value(PublicInstanceProperty) Specifiesa numericvalue thatrepresents thecurrent positionofthe scrollboxonthescrollbar.

Scroll(PublicInstanceEvent) Occurswhen thescrollbox hasbeen movedbya mouseor keyboard action.

ValueChanged(PublicInstanceEvent) Occurswhen thevalue propertyhaschanged (typicallyviaa scrollevent,or programmatically).

Chapter29:IrregularFormsShapesTherearereallyonlyahandfulofshapesinthetoolkitofirregularformscreation. Thankfully,though,youonlyneedafew.Nearlyeveryshapecanbecreatedfroman ellipseorapolygon.Shapessuchascirclesandtrianglesarereallyonlyspecialcasesorcombinationsofthesetwofigures.Otheritemsthatcanbedrawnincludearcs,Beziers, curves,andlines.Thischapterprimarilydealswithclosedshapes.

GraphicsDrawinganirregularform,likedrawinganything,requiresfourthings:asurface,astylus, acolor,andsomethingtodraw.ThissectiondetailswhatobjectsintheFramework equatetotheserequireditems.Specialcareisgiventothoseobjectsthatarecomplexor usedfrequently.

SurfaceThesurfaceuponwhichyoudrawisequivalenttotwodifferentobjectswithinthe Framework:theGraphicsobjectandtheRegionobject.TheGraphicsobject providesthemethodsfordrawingtothedevicecontext.Adevicecontextisanalogousto acoordinatesystemlaidontopoftheform.Usefulitemssuchaspositioncanbe extrapolatedfromthisobject.Thisessentiallymeansthatthedrawingsurfaceoftheform,asrepresentedbytheGraphicsobject,canbedirectlyusedbyyourapplication.

PartVI:VB .NET and the Web Chapter31:IntroductiontoWebDevelopment Chapter32:IntroductiontoASP.NET

Chapter33:PageFrameworkChapter34:HTMLServerControlsChapter35:WebControls Chapter36:ValidationControlsChapter38:EventsChapter39:CascadingStyleSheetsChapter40:StateManagement

Chapter42:TracingChapter43:Security

Chapter31:Introduction to Web DevelopmentLanguages and Technologies of the WebThenumberofWebpagesontheInternetisenormous,andthelanguagesthatbuilt thesepagesarenumerousaswell.EventheuntrainedobservercanseeitintheURL extensionsthatareoutthere.Someoftheextensionsincludehtml,asp,jsp,cgi, perl,js,php,andmanymore.Thisisduetotheplethoraoflanguagesouttherethata programmercanusetobuildaWebpage.

HTMLHypertextMarkupLanguage(HTML)isalanguageusedtopresentinformationtothe browserfordisplay.HTMLisnotatrueprogramminglanguage—itwon'tallowyouto applyanylogic.Itisbasicallyacollectionoftagsthatbrowsersinterprettoapplystylesto text.HTMLcanalsoprovidelinkstootherpages,showimages,andpresentbasicforms.ThetagsinHTMLareenclosedwithinanopeningless-thansign(<)andaclosing greater-thansign(>).ItisimportanttonotethatdifferentbrowsersinterpretHTML differently,andnotallthetagsareequallyidentifiedineachofthevariousbrowsers.

CascadingStyleSheets(CSS)CascadingStyleSheets(CSS)isanoutstandingadditiontoHTMLthatallowsyouto applyacertainstyletoaparticularHTMLtag.Forinstance,ifyouwanteach<h1>tagin yourpagetobebold,beinArialfont,andhaveafontsizeof15,youcanapplyHTML<font>tagsaroundeachinstance.Thiscansometimesbeverytime-consuming,andcanmakeforsomemessycode.Byapplyingastylesheettothepage,youcanspecify howevery<h1>tagisformatted,whichsavestimeandallowsforcleanercode.

<html>

<head>

<title>MyHomepage</title>

<styletype="text/css">

body{

font-family:Arial,Helvetica,sans-serif;

font-size:smaller;

color:Red;

font-weight:bold;

}

</style>

</head>

<body>

HelloWorld!

</body>

</html>

JavaScript

Table31-1:T-SQLCommands

T-SQL

Description

Select Selectsspecifieddatafromthechosentable.The programmercanthenusethisdatainanumberof differentways.

Insert Insertsarowofdataintothedatabase.Itbasically createsanewrowoftabledata.

Update Updatesachosennumberofrowsofdata.Byupdating tabledata,dataischangedpermanantlywithinafield.

Delete Deletesaspecifiednumberofrows.Itispossibleto deletefromonerowofdatatoeveryrowinthe database.

JavaScriptisanoutstandingprogramminglanguagethatallowsyoutoprogramboth client-andserver-sideactions.MostdevelopersuseJavaScripttoperformactionsonthe client-side,whichallowsthemtoprogramforcertaineventstheusermakesonthepage. Forinstance,youmayhavenoticedthatifyouhoveryourcursoroveranimage(usuallyabutton),itchangestoadifferentimage.Thisiscalledarollover,andthisfunctionalityisusuallydoneinJavaScript.Itisbasedonanevent(thehoveringofthecursoroverthe image).Youcanusuallyprogramforanumberofdifferenteventsonthesamepage, suchasbuttonclicks,mouseovers,pageloads,andmore.

<html>

<head>

<title>MyHomepage</title>

</head><body>

<scriptlanguage="JavaScript"type="text/javascript">



</script>

</body>

</html>

Transact-SQLYes,thereisanSQLServerprogramtobuilddatabases,butthereisalsoaprogramminglanguagethatallowsyoutoprogramtransactionsagainstthisdatabase.ItiscalledTransact-SQL(orT-SQL).ToprogramagainstanOracledatabase,youwouldusePL-SQL,whichissimilartoT-SQL,butwithslightlydifferentsyntax(it'smorelikeC).

UsingT-SQL,youcansendawidevarietyofcommandstothedatabase.Hereisashort listofsomeexamples: Toselecttheentiretableofdatafromthedatabase,useSelect*

fromCustomers. Toselectonlyaselectedrowofdata,useSelect*from

Customerswherecustomerid=11. Toselectonlycertaininformationandthenreorderthedatabasedupon

selectedparameters,useSelectfirstname,lastnamefrom Customersorderbylastname.

Thelastexampleselectsthefirstnameandthelastnameofeachpersoninthe Customerstable.T-SQLthenrearrangesthisdatabasedonthecustomers'lastnames. WithT-SQL,itisalsopossibletousevariousothercommandstoperformtheactions neededinthedatabase.Table3 1 - 1liststhemaincommandstouseinT-SQL statements.

ADO2.6andADO.NET

Microsoft'sADO.NET,thelatestversionafterADO2.6,isacollectionofobjectsthat programmersusetomanagedata.ADOstandsforActiveXDataObjects.ThislatestversioniscalledADO.NET

ASP.NET

Initssimplestform,ASP.NETisanewtechnologyavailablewiththe.NETFramework thatallowsyoutobuildWebFormsandWebServices.ASP.NETcontainsacollectionof controlsthatyoucanprogram.Althoughitcontainsacollectionofbuilt-incontrols,it enablesyoutodevelopyourowncontrols.ASP.NETallowsyoutodevelopWeb-based applicationsinthesamemannerasaVisualBasic.NETWindowsForm.Thisnew technologyalsohassomeoutstandingnewfeaturesthatwerenotavailableinclassic ASPsuchaswaystomanagestateaswellasnumerousoptionsthatareavailableinthe configurationofyourapplications.

Chapter32:IntroductiontoASP.NETWithASP.NET,MicrosoftsetasideVBScript,andalloweddeveloperstousericher languagestodevelopserver-sidecode.DeveloperscannowuseVB.NET,C#,orJScript.NETtocodetheirWebpages.ThischapterwillfocusonusingVB.NETforWeb development.

Why ASP.NET?ASP.NETisanintegratedWebdevelopmentplatformthatallowsyoutousevarioustoolstobuildrichWebapplications.Thisnewtechnologyoffersgreatnewadvancesinstatemanagement,scalability,caching,deployment,security,performanceandsupportforaWebservicesinfrastructure.ASP.NETalsocontainsacollectionofcontrolstouseandbuildonwithinthecontextofaWebpage.ASP.NETisnotreplacingASP3.0.ASP.NETwasdevelopedbyMicrosoftasActiveServerPagesPlus(ASP+),andlater gotanamechangetoASP.NETandbecamepartofthe.NETfamily.

ASP.NETcontrols

ASP.NETincludesanumberofcontrolstoprogram.ThesecontrolsareusedwithinaWebFormtoproduceformswiththeexactfunctionalitythatyourequire.ForusewithintheWebFormareanumberofnewavailablecontrolssuchasHTML controls,Webcontrols,Validationcontrols,andUsercontrols.Itispossibleforyouto programthesecontrolsusingVB.NETtoprovidespecificfunctionality.

Now,ASP.NEThasasetofValidationcontrolsthatallowyoutospecifyclient-side validationrules.ASP.NETwilltakecareoftheJavaScript,andwillcodetheJavaScript basedonthebrowsertheuserisviewingthepagewith.

ASP.NETcomparedtoASP3.0

ASP.NETprovidesanumberofnewandexcitingfeatures.Bymakingsomebasic comparisonsofASP.NETtoASP3.0,youwillseewhyASP.NETprovidesabetterway tobuildWebpages.ASP.NETintheendwillmakeforeasierandfasterdevelopment, andtheapplicationsbuiltonthiswillbebetterandfaster.

PageextensionsThefirstnoticeabledifferenceisthatpagesbuiltusingASP.NETusetheaspxextension insteadoftheaspextensionthatisusedinASP3.0.WithtraditionalASP,wheneverthe servercametoanasppage,itsentthepagetobeprocessedbytheasp.dll,whereas theaspxpagesofASP.NETaresenttothexspisapi.dll.

Asstatedearlier,traditionalASPpagescanrunside-by-sidewithASP.NETpages.

Basedontheextensions,theywillbesenttotheappropriateDLLforprocessing.

Itisnotpossibletojustchangetheextensionnameofthefiletomagicallycreatean ASP.NETpage.YouwouldcreateanASP.NETpageonlybyextension,andyouwillget apagefulloferrorsifyoutry.

LanguageneutralityAmajorityoftraditionalASPdevelopersusedVBScriptasthescriptinglanguageto programtheirASPpages.WithASP.NET,VBScriptisnomore.ASP.NETdoesnotlimit itselftowhichlanguageitneeds.ASP.NETallowsyoutouseanyofthe.NETlanguages tousewhenprogrammingyourASP.NETpages(forexample,VB.NETandC#). ASP.NETisasetofcontrolsthatyoucanplaceonapagetoprovidespecific functionality,andyouuseotherlanguagestoprogramarichersetoffunctionalitiesand attributechanges.Nomatterwhich.NETlanguageyouusewhenyoubuildanASP.NET application,youhaveaccesstothesamecontrolsandfeaturesthateveryoneelsehas accessto.Youcanevenplugpiecesintoyourapplicationandnotbeconcernedabout which.NETlanguagetheywereprogrammedin—becauseitwon'tmakeanydifference. Alltheselanguagesworktogetherunderthesamesetofrules.

CodeseparationASP.NETincludesagreatnewfeaturecalledCodeBehind.WhendevelopingASP pages,thedeveloperwouldtraditionallyintermingleanumberoflanguageswithinone page(IrecentlydevelopedapagethatcontainedHTML,ASP,DHTML,JavaScript,and someCSS).Thepage,whencalledbyabrowser,wouldbeprocessedthroughthe asp.dllinalinearfashion,onelineatatime—startingatthetopofthepage.Withthis numberoflanguagesonasinglepage,thedevelopercouldhaveareallycomplicated pagetomaintainandupdate.Somedeveloperscallthisspaghetticode,andwithgood reason!

Therewerealsomanysituationsinwhichyoucouldhavemultipledevelopersworkingon oneASPpage.YoucouldhaveanHTMLdeveloperandanASPdeveloperworkingon distinctsectionsofthepage.Then,theJavaScriptwizardofthegroupwouldjumpinand startprogrammingsomeclient-sidecode.Witheveryonecodinghisownsections,the codewouldsometimesgetrathermessy.However,ASP.NETprovidesthemeansforprovidingthepage'slogic,theVB.NETcode,withinaseparatefile:theCodeBehindfile(seeFigure3 2 - 1 ).Thisallowspeopletoworkintheirownsettings,andnotbumpintooneanotherasthepagedevelops.Thisis alsothepartofthepageinwhichthedevelopercanprogramevent-drivenroutines.The authorswillbedoingalltheCodeBehindfilesinVB.NET,evenifitisalsopossibleto codetheminC#.

Figure32-1: AnexampleofaCodeBehindpage.NoticethatthepageiswrittenasWebForm3.aspx.vbonthetab.

EachcontrolthatisinthepresentationlayercanbecontrolledintheCodeBehindpage. EveneventsthathavenothingtodowiththeWebcontrolscanbeplacedinthe CodeBehindpage,suchaseventsforwhenthepageinitializesorisposted.

StatemanagementTraditionalASPcoulddealwithsessionsasameansofstatemanagement,althoughthis gotratherdifficultwhendealingwithaWebForm.IfauserrequestsanASPpagefrom

Table32-1:ASP.NETSessionObjects

SessionType Description

In-processmode Asession thatrunsin- process. Thisisthe default settingand isthesame astheASP 3.0session.

Out-of-processmode This session managementrunsout-of-process, andstores thesession information onthesame serveroran entirely different server.

SQLServermode Allowsfor thestoring ofsessions ina backend database.

Cookielessstate Forclients whochose nottotake advantage of the ASP.NET session state.

ServerA,atthesametimecreatingasession,andthenrequestsanASPpageserved fromServerB,thesessionwasimpossibletopassbetweentheservers.ASP.NETprovidesacompleteandrobustmeansofprovidingstatemanagement,however.Table3 2-1describesvariousASP.NETsessionobjects.

WebFormsWebFormsconsistofthetraditionalformsyoucanbuildinanyHTMLpage.WebForms areusedwheneverthereissomeinteractionwiththeuseronthepage.Someexamplesincludeanyoftheformelements,suchastextboxes,radiobuttons,andcheckboxes. Theseelementsdemandinteraction,andthereforeneedtobeencapsulatedwithina WebForm.WithWebForms,youcanreallygetdowntodetailandmakeeachaspectof theformfunctionasyouseefit.Youwillbebuildingalargenumberofformsinthe chaptersthatfollow.

DevelopingWebFormsisfairlystraightforward,andcanbedoneinacoupleofdifferent ways.ThefirstwayisthemethodthatmostASPprogrammersuse:codingeachofthe elementsstraightintothecodewindowofthepage(HTMLmode).Thesecondwayis morefamiliartotraditionalVisualBasic6.0developers:usingVisualStudio.NETto simplydraganddroptheitemsontothepage,therebybuildingtheform(Designmode).

Web ServicesAlthoughthispartofthebookdescribeseverythingyouneedtoknowtogetstarted buildingVB.NETWebFormsusingASP.NET,itisalsopossibletobuildASP.NETWeb Services.WebServicesareusedtoremotelycallaspecificfunctionalityacrosstheInternetusing XMLtotransportthedata.Wewon'tbediscussingWebServiceswithinthissectionof thebook.

XMLEveryoneistalkingaboutXMLtoday.Eveniftheydon'tknowwhatitisorwhatitdoes, peopledoknowthatitisimportant.Youhaveprobablyheardbusinessmanagersasking theirITcolleagues,"Yeah,butdoesitsupportXML?"(Ironically,theyhadproblems openingtheirbrowsersandpullingupthecompany'sWebsitethedaybefore.)

WithinASP.NET,XMLhasstrongersupportthanitdidwithASP3.0.Thegreatthingis thatwithASP.NET,youcannowread,write,oreditXMLasyouseefit.XMLis becomingmoreandmorepopularwiththeevolutionoftheInternet.Itisagreattoolto useforhandlingdata.

SecurityASP.NEToffersatremendouslybettersecurityfeatureset.Withtheweb.configfile, youcannowmodifysecuritysettingsinonespotinyoursystem,andthosechangeswill takeeffectimmediatelywithoutstoppingandstartingIIS.WithASP.NET,youcanusea widevarietyofauthenticationandauthorizationmodels,suchasWindows,Forms,and Passportauthentication.

CreatingyourfirstWebapplication

PullupVS.NET.DependingonhowyouhavetheIDEconfigured,youshouldseetheStartPage,aswellastheSolutionExplorerandtheemptyPropertiesBox.TheStartPagelistsanyapplicationsthatyoumayhavealreadystarted.Tobuildyour newapplication,clickNewProjectwithintheStartPage.TheNewProjectdialogbox displays(seeFigure 3 3 - 3 ).

Figure33-3: TheNewProjectdialogbox

Forthepurposesofthisbook,selecttheVisualBasicProjectsfolder.Youseea selectionoftemplatesintherightwindowofthedialogbox.Thelistofdialogboxes includethefollowing:

WindowsApplication ClassLibrary WindowsControlLibrary ASP.NETWebApplication ASP.NETWebService WebControlLibrary ConsoleApplication WindowsService EmptyProject EmptyWebProject Newprojectinexistingfolder

YoushouldselectASP.NETWebApplication,whichisaprojectforcreatingan applicationwithaWebuserinterface.Nametheapplicationwhateveryouwant,andthe locationwheretheapplicationwillresideshouldbehttp://localhost/.Afteryou configurethisdialogbox,clickOpen.VS.NETthencreatesanapplicationfolderwithinyourwwwrootfolder.Withinthefolder, itplacesanumberoffilesthatareimportantforyourapplication.Youcanviewallthese filesthatarecreatedwithintheSolution

ExplorerboxinVS.NET (seeFigure 3 3 - 4 ).

Figure33-4: TheSolutionExplorerallowsyoutoviewallthefileswithinyoursolution.

VS.NETwillhavecreatedthefollowingfilesforyourapplication: References:Thisisafolderthatcontainsapplicationreferencesto

.NETFrameworknamespaces.IfyouopenthefolderwithintheSolution Explorerwindow(clickonceontheplussignnexttothefolder),youwill noticewhatnamespacesarethereatthatmoment.Atthispointyour applicationisreferencingonlySystem,System.Data, System.Drawing,System.Web,System.Web.Services,and System.XML.

AssemblyInfo.vb:ThisVB.NETfilecontainsalltheinformationforyourassembly,suchasversioninganddependencies.

Global.asax:SimilartotheGlobal.asafilefromASP3.0.Thisisthe ASP.NETapplicationfileinwhichyoucanplacecodetorespondto application-levelevents.

Styles.css:ACascadingStyleSheetfilethatappliesstylestoyourdocuments.

Web.Config:Theconfigurationfilethatcontainstheapplication settings.ThisisanXML-basedfilethatiseasytounderstand.

WebApplication1.vsdisco: ThisisanXMLfilethatcontains informationallinksaboutanASP.NETWebService.

WebForm1.aspx:ThisisthefirstWebFormASP.NETpageforyour application.Ifyouwant,right-clickthefileandrenameitdefault.aspx.

WorkingwithyourfirstWebFormNowthatyouhaveyourfirstWebFormopen,noticethatyouseeapagethatcontainsa lotofdotsthroughoutthepage.ThismeansthatyouareworkingwithintheGridLayout mode.TochangetotheFlowLayoutmode,clickanywherewithinthedesignarea. NoticethatalonglistofpropertiesnowappearswithinthePropertiesbox(seeFigure33 - 5 ).ScrolldownuntilyoufindthepageLayoutproperty,andchangeitthere. FlowLayoutmeansthatallthecontrolswillbelaidoutinaleft-rightandup-down manner.GridLayoutlaysoutthecontrolsbaseduponXYpositioning,similartothe wayitwasinVisualBasic6.0.ASPdeveloperswillbemorefamiliarwiththe FlowLayoutmo

de,andVisualBasic6.0developerswillbemorefamiliarwiththe GridLayoutmode.

WorkinginDesignmode

IfyouworkinDesignmode,youseetheToolboxontheleftsideoftheVS.NET application.ClickingtheWebFormstabwithintheToolboxdisplaysalltheWebcontrols andValidationcontrols.TheHTMLtabshowsyoualargelistofHTMLelementsthatcan beconvertedtoHTMLServercontrols.TobuildaformwithinDesignmode,justdrag-and-dropyourselectedcontrolsontothepage.ToapplyanyVB.NETcodetothecontrol,justdouble-clickthecontrol.Youwill seetheCodeBehindpage,whichisaseparatecontainerforallyourserver-sidecode.It alreadycreatedaPage_Loadroutineforyouaswellasaroutineforthecontrolthatyou justclicked.

Usingthetabsatthetop,youcanswitchbetweenyourCodeBehindpageandthe Presentationpagewithease.Double-clickinganycontrolreturnsyoutotheCodeBehind page.

Afteryoufinishbuildingyourapplication,right-clickthefilewithintheServerExplorer box,andchooseBuildandBrowse.Thissavesthefileandrunsthefilethrougha browser,butallwithinVS.NET.Ifthereareerrorsonthepage,VS.NETwillinformyou ofthoseerrors.

Workingwithcontrols

Youcanalsoworkwiththecontrol'spropertiesorattributeswithintheDesignmodeofVS.NET.Clickonceonthecontrolthatyouwanttoworkwith,andnoticethatallthecontrol'spropertiesappearinthePropertiesbox.Changinganyofthepropertiesherewillbereflectedbacktothecontrol.Afterchangingthepropertiessothatthecontrolisas youwantit,clickHTMLmodeandseehowVS.NETalteredthecodetoreflectthe changesyoumadeinDesignmode.

AddingmorefilesItisquiterarewhenanInternetapplicationcontainsonlyonepage.Youusuallyneeda numberofpages.TocreateanotherpagewithinVS.NET,right-clickyourapplication withintheServerExplorerboxandselectAdd.ScrolldownandchooseAddNewItem. YouwillbepresentedwiththeAddNewItemdialogbox(seeFigure 33 - 6 ).

Figure33-6: AccesstheAddNewItemdialogboxtocreateanotheritem.

Youseethefollowingitems,allofwhichcanbeaddedtoyourapplication: WebForm:CreatesaWebForm.aspxfileinyourapplication.Thisisthe formforWebapplications. WebService:CreatesaService1.asmxfileinyourapplication.Thisis

avisuallydesignedclassforcreatingaWebService. Class:CreatesaClass1.vbfileinyourapplication.Thisisanempty classdeclaration. Module:CreatesaModule1.vbfileinyourapplication.Thisisafilefor storinggroupsoffunctions. ComponentClass:CreatesaComponent1.vbfileinyourapplication.

Thisisaclassforcreatingcomponentsusingthevisualdesigner. DataFormWizard:CreatesaDataWebForm1.aspxfileinyour

application.ThisisadataformforWebapplications. DataSet:CreatesaDataset1.xsdfileinyourapplication.Thisisafile

forcreatinganXMLschemawithDataSetclasses. WebUserControl:CreatesaWebUserControl1.ascxfileinyour

application.ThisisanASP.NETservercontrolcreatedusingthevisual designer. HTMLPage:CreatesanHTMLPage1.htmfileinyourapplication.Thisis

anHTMLpagethatcanincludeclient-sidecode. Frameset:CreatesaFrameset1.htmfileinyourapplication.Thisisan

HTMLfilethathostsmultipleHTMLpages. StyleSheet:CreatesaStyleSheet1.cssfileinyourapplication.This

isacascadingstylesheetusedforrichHTML-styledefinitions. XMLFile:CreatesanXMLFile1.xmlfileinyourapplication.Thisis basicallyablankXMLfile. XMLSchema:CreatesanXMLSchema1.xsdfileinyourapplication.

ThisisafileforcreatingaschemaforXMLdocuments. XSLTFile:CreatesanXSLTFile1.xsltfileinyourapplication.Thisis

afileusedtotransformXMLdocuments. WebCustomControl:CreatesaWebCustomControl1.vbfileinyour

application.ThisisaclassforcreatinganASP.NETservercontrol.

CodeFile:CreatesaCodeFile1.vbfileinyourapplication.Thisis basicallyablankcodefile. DynamicDiscoveryFile:CreatesaDisco1.vsdiscofileinyour

application.ThisisafileusedtopublishinformationaboutaWebService.

StaticDiscoveryFile:CreatesaDisco1.discofileinyour application.ThisisafileusedtopublishinformationaboutaWeb Service.

GlobalApplicationClass:CreatesaclassforhandlingWebapplicationevents.

WebConfigurationFile:CreatesafileusedtoconfigureWeb applicationsettings. TextFile:CreatesaTextFile1.txtfileinyourapplication.Thisisa blanktextfile. InstallerClass:CreatesanInstaller1.vbfileinyourapplication.

Thisisaclasstobeinvokedatsetuptime. CrystalReport:CreatesaCrystalReport1.rptfileinyour

application.ThisisaCrystalReportfilethatpublishesdatatoaWindows orWebForm. BitmapFile:CreatesaBitmap1.bmpfileinyourapplication.Thisisa

Win32bitmapfile. CursorFile:CreatesaCursor1.curfileinyourapplication.Thisisa

Win32cursorfile. IconFile:CreatesanIcon1.icofileinyourapplication.Thisisa

Win32iconfile. AssemblyResourceFile:CreatesaResource1.resxfileinyour

application.Thisisa.NETresourcefile. AssemblyInformationFile:CreatesanAssemblyInfo1.vbfilein

yourapplication.Thisisafilecontaininggeneralassemblyinformation. JScript:CreatesaJScript1.jsfileinyourapplication.Thisisascript filecontainingJScriptcode. VBScript:CreatesaVBScript1.vbsfileinyourapplication.Thisisa scriptfilecontainingVBScriptcode. WindowsHostScript:CreatesaWindowsScript1.wsffileinyour

application.ThisisafilecontainingscriptthatisrunasaWindows program.

Chapter34:HTMLServerControlsXHTML-Compliant CodeWhenwritingHTMLServercontrolstoprogram,itisveryimportanttowritethecontrols sothattheyareXHTML-compliant.

Therulesarefew andfairlystraightforward.Thefirstruletofollowisthattagsarenested properly.Tonesttagsproperly,youneedtoopenandclosetheminaspecificorder.The ruleis to closethetagsin thereverseorderin whichyouopenthem.Forinstance,ifyou openTagAandthenyouopenTagB,youcannotcloseTagAuntilyoucloseTagB.

INCORRECT:

<ahref="somepage.aspx"><b>Hello World!</a></b>Asyoucanseefromthefollowingexample,youopenthe<a>tagandthenopenthe<b>tagtomakethelinkbold,butyouclosedthe<a>tagbeforeyouclosedthe<b>tag. ThisisnotXHTML-compliantcode.Thiscodeshouldinsteadbewrittenasfollows:

CORRECT:

<ahref="somepage.aspx"><b>Hello World!</b></a>

Itisalsoimportanttonotethatforeveryopeningtag,theremustbeaclosingtagforall tagsthathaveclosingtags.So makesurethatwheneveryouopenanyof theseHTML tags,youalsoclosethetagintheproperplacewithinthedocument.Fortagsthataresingularelements,younowneedtoendthetagwitha/>toclosethetaginordertobeXHTML-compliant.Forinstance,the<hr>tagdoesnothaveopeningandclosingtags,instead,itisasingularelement.WithXHTML,youwouldnowdisplay the<hr>tagas<hr/>whenyouareprogrammingit.

Common Tag AttributesInorderfortraditionalHTMLelementstoworkasHTMLServercontrols,youhavetoadd somecommonattributestoworkagainstinordertochangetheelement'sfunctionality. ThefirstattributethateveryHTMLServercontrolmustcontainisarunat=server

withinthetagitself.Theattributerunat=servertellstheprocessingserverthatthetag isprocessedontheserver,andisnottobeconsideredasatraditionalHTMLelement. Also,thetagmustcontainanIDattributeinorderfortheservertoidentifyitandforyoutoprogramit.ThefollowingexampleisaHTMLServercontrol.

<aid="FirstLink"runat="server">ClickMe!</a>This<a>taghasbeenturnedintoanHTMLServercontrolbyitsinclusionoftheIDand therunat=serverattributes.

Overview of HTML Server ControlsASP.NETServercontrolsaregroupofnewcontrolsprovidedby.NET.HTMLServer controlsareonetypeofcontrolnowavailable.OthertypesincludeWebServercontrols andValidationcontrols.Figure34 - 1 showsthehierarchyofHTMLservercontrolsintheSystem.Web.UI.HtmlControlsnamespace.

Figure34-1: HierarchyofHTMLServercontrolsHTMLServercontrolsmapdirectlytotheircorrespondingHTMLelements.When convertingASP3.0pagestoASP.NETpages,usingHTMLServercontrolsisaless- painfulsolutionthanusingASP.NET'sWebcontrols(discussedinthenextchapte r ). Table3 4 - 1describesthesecontrolsinmoredetail.

Table34-1:HTMLServerControlsQuicklist

Control RelatedHTMLTagHTMLAnchor Allowsaccesstoprogramagainstthe<a>

tag.HTMLButton Allowsaccesstoprogramagainstthe

<button>tag.HTMLForm Allowsaccesstoprogramagainstthe

<form>tag.HTMLGeneric ThiscontrolallowsaccesstoHTMLtagsthat

arenotrepresentedbyanyHTMLServer controlspecifically;forexample,the<span>,<div>,and<font>tags.

HTMLImage Allowsaccesstoprogramagainstthe<img>tag.

HTMLInputButton Allowsaccesstoprogramagainstthe<inputtype=button>,<input type=submit>,and<input type=reset>tags.

HTMLInputCheckbox Allowsaccesstoprogramagainstthe<inputtype=checkbox>tag.

HTMLInputFile Allowsaccesstoprogramagainstthe<inputtype=file>tag.

HTMLInputHidden Allowsaccesstoprogramagainstthe<inputtype=hidden>tag.

HTMLInputImage Allowsaccesstoprogramagainstthe<inputtype=image>tag.

HTMLInputRadioButton Allowsaccesstoprogramagainstthe<inputtype=radio>tag.

HTMLInputText Allowsaccesstoprogramagainstthe<inputtype=text>and<input type=password>tags.

HTMLSelect Allowsaccesstoprogramagainstthe<select>tag.

HTMLTable Allowsaccesstoprogramagainstthe<table>tag.

HTMLTableCell Allowsaccesstoprogramagainstthe<td>and<th>tags.

HTMLTableRow Allowsaccesstoprogramagainstthe<tr>tag.

HTMLTextArea Allowsaccesstoprogramagainstthe<textarea>tag.

Chapter35:WebControlsWithinASP.NETServercontrols,Webcontrolsareonetypeofcontrolthatisnow available.OthertypesincludeHTMLServercontrolsandValidationcontrols.

BetweenWebcontrolsandHTMLServercontrols,Webcontrolsarethemore sophisticatedcontroltype.Theyallowahigherleveloffunctionalitythatisnotfoundin HTMLServercontrols.

UnlikeHTMLServercontrols,whichmapdirectlytotheircorrespondingHTMLelements, WebcontrolsgenerateHTMLcodebaseduponfunctionalityandthevisitingclient's browsertype.WithWebcontrols,youmightsaythatyouwantatextboxinyourWeb Form.Youcanchangethestyleofthetextboxbyjustchangingthepropertiesofthetext boxcontrolitself.Bychangingtheseproperties,youcanspecifywhetherthecontrol shouldoutputaregulartextbox,apasswordtextboxoratextarea.Whensomeonehits thatparticularpage,ASP.NETsendstotheclientthecodethatisappropriateforthat

browser.EachbrowsermayseedifferentHTMLcode,dependingonwhattheirbrowser supports.ASP.NETtakescareofallthebrowserdetectionandtheworkthatgoeswith thisforyou.

HTMLServerControlsversusWebControlsAWebcontrollookslikethis:

<asp:Label[attributes]>HelloWorld!</asp:Label>

OneimportantdifferencebetweenHTMLServercontrolsandWebcontrolsisthatthe attributesinHTMLServercontrolsarespecifictothatHTMLelement,buttheattributes withinWebcontrolsarespecificforthecontrolitself,notfortheHTMLthatisgenerated baseduponthecontrol.Whendecidingwhattypeofcontroltouse,youshouldbaseyourchoiceonwhatcontrol offersthespecificfunctionalitythatyourequire.Table3 5 - 1 summarizeswhentouse HTMLServercontrolsandwhentouseWebcontrols.Table35-1:HTMLServerControlsversusWebControls

ControlType

WhentoUseThisControl

Webcontrol Whenyourequirearichersetoffunctionalitytoperform complicatedpagerequirements.

WhenyouaredevelopingWebpagesthatwillbeviewed byamutitudeofbrowsertypesthatwouldrequiredifferent codebaseduponthesetypes.

WhenyoupreferamoreVisualBasic-typeprogramming modelthatisbasedontheuseofcontrols.

HTML Server control

WhenconvertingtraditionalASP3.0Webpagesto ASP.NETWebpages,andspeedisaconcern.You'llfind thatitisaloteasiertochangeyourHTMLelementstoHTMLServercontrolsratherthenchangingthemtoWeb controls. WhenyoupreferamoreHTML-typeprogrammingmodel.

Web Controls and How to Program for Them

Webcontrolscanbeassimpleandascomplexasyouwantthemtobe,butingeneral, theyareveryeasytousewithinyourpages.Figure35 - 1showsthehierarchyofWebcontrolsintheSystem.Web.UI.WebControlsnamespace.

Figure35-1: HierarchyofWebcontrolsYouneedtocodeWebcontrolsinanXHTML-compliantway,meaningthatyoumust

properlynesttags.Closethetagsthataresingularelementswith/>.Forinstance,you canwritetheLabelcontrolasthefollowing:

<asp:labelrunat="server"id="label1"></asp:label>

Or,youcanwritetheLabelcontrolasthefollowing:

<asp:labelrunat="server"id="label1"/>

Table3 5 - 2 givesabriefdescriptionofthecontrolsthatarecoveredinthischapter.

Table35-2:WebControls

WebControl Description<asp:adrotator> Similartothe traditional ASP adrotator component. Thiscontrol displaysa

specified orderof images.Itis alsopossible tosetthe sequenceof imagestobe random.

<asp:button> Usedto performatask orinitiatean event.Usedto submitformstotheserver.

<asp:calendar> Arichcontrol thatdisplaysa graphical calendar,and allowstheusertoselectadatethat caninitiatean eventonthe page.

<asp:checkbox> Displaysa traditional HTMLcheck boxthat allowsuserstoclickitonoroff.

<asp:checkboxlist> Agroupof checkboxes thatallowfor mutiple selections.

<asp:datagrid> Alistcontrol thatallows data-bound informationto bedisplayed intables.The tablescanbeconstructedtoallowfor editingandsorting.


WebControl Description

<asp:datalist> Alistcontrol thatallows data-bound informationto bedisplayed. Construction ofthedisplay isdoneby usinga customizable template.

<asp:dropdownlist> Displaysa traditional HTMLselect tagthatallows userstoselect anitemfroma drop-downlist ofitems.

<asp:hyperlink> Displaysa traditional HTML hyperlinkthat usersclickto performan event(suchasgoingtoanewpage).

<asp:image> Displaysan image.

<asp:imagebutton> Thesameas aButton control,but allowsan imagetobe usedforthe button.<asp:label> Displaystext thattheuser cannotedit directly.

<asp:linkbutton> Thesameas aButton control,but lookslikea hyperlink.

<asp:listbox>Similartothe drop-downlist control,but insteadofseeingjust onelistitem, theusercan seemultiple listitems.It alsooptionally allowsfor mutiple selections


WebControl Description<asp:literal> Displaysstatic text.

<asp:panel> Createsa borderless divisiononthe formthat servesasa containerfor othercontrols.

<asp:placeholder> Reservesa locationinthe pagecontrol hierarchyfor controlsthat areadded programmatic ally.

<asp:radiobutton> Displaysa traditional HTMLradio button.

<asp:radiobuttonlist> Displaysa groupof traditional HTMLradio buttons.The usercan selectonly

onechoice fromthe group.

<asp:repeater> Alistcontrol thatallowsfor data-bound informationto bedisplayed usingany numberof controlsasa template.

<asp:table> Displaysa traditional HTMLtable.


WebControl Description<asp:textbox> Displays a traditional HTML text box.

<asp:xml> DisplaysXML documents, andallows XSL documentsto transform them.

DataBinding

DataisveryimportanttoalmosteveryWebapplication.Today,itisquiteraretopresent onlystatictextandimageswithinyourWebdocuments.Itisdatafromavarietyof sourcesthatisdrivingcurrentWebpages.

ThiswasthegreatthingaboutASP3.0.Youcoulddeveloppagesthatwouldrender whentheuserpulledupthepageinthebrowser.Asitwasrendering,thepagewould grabdatafromallsortsofsources,andplacethisdatainappropriateplaceswithinthe documentforpresentation.ItisimportanttonotethatwithDataBinding,thecontrolisnotconnectedtothedatasource.Instead,whatyouaredoingismakingacopyofthedataandthenbindingthis copywiththeServercontrol.

WithDataBinding,notonlycanyouconnecttotraditionaldatasourcessuchas relationaldatabases,butyoucanalsomakeconnectionstoawidevarietyofotherdata sources.Youcanconnecttoanyofthefollowingdatasourcesandmore:

DataSets XMLfiles Arraylists Hashtables Properties Expressions Functions Collectionsandlists

Tobindtodatasourcestobeusedincomplexcontrolssuchasthe<asp:datalist>,<asp:datagrid>,and<asp:repeater>controls,youusetheDataBind()method

ListBoundcontrolsTherearethreeListBoundcontrolstousewithinyourapplications:<asp:datalist>,<asp:datagrid>,and<asp:repeater>.Allthreecontrolsofferoutstanding programmingfunctionalitytoyourWebpagesbyallowingyoutospecifythelayoutand appearanceofrowsofdata.Thedatathatthesecontrolspresentisdatathatyouwould bindthecontroltofordisplaying,updating,insertingand/ordeleting.

<asp:datalist>TheDataListcontrolallowsyoutodisplaydataonaWebpageusingcustom templatesandstylesthatyoudefine.Withinthecodeofthedocument,theDataList controliswrittenas<asp:datalist>.ThereareoptionswithintheDataListcontrol thatallowuserstoeditanddeletedataaswell.Thefollowingexampleshowstheuseof theDataListcontrol:

<asp:DataListid="DataList1" CellPadding="pixels"

CellSpacing="pixels" DataKeyField="DataSourceKeyField"

DataSource='<%databindingexpression%>'

ExtractTemplateRows="True|False" GridLines="None|Horizontal|Vertical|

Both" RepeatColumns="ColumnCount" RepeatDirection="Vertical|

Horizontal" RepeatLayout="Flow|Table" ShowFooter="True|False"

ShowHeader="True|False"

OnCancelCommand="OnCancelCommandMethod"

OnDeleteCommand="OnDeleteCommandMethod"

OnEditCommand="OnEditCommandMethod"

OnItemCommand="OnItemCommandMethod"

OnItemCreated="OnItemCreatedMethod"

OnUpdateCommand="OnUpdateCommandMethod" runat="server">

<AlternatingItemStyleproperty="value"/>

<EditItemStyleproperty="value"/>

<FooterStyleproperty="value"/>

<HeaderStyleproperty="value"/>

<ItemStyleproperty="value"/><SelectedItemStyleproperty="value"/>

<SeparatorStyleproperty="value"/><HeaderTemplate>HeadertemplateHTML

</HeaderTemplate>

<ItemTemplate>

ItemtemplateHTML

</ItemTemplate>

<AlternatingItemTemplate>AlternatingitemtemplateHTML

</AlternatingItemTemplate>

<EditItemTemplate>

EditeditemtemplateHTML

</EditItemTemplate>

<SelectedItemTemplate>SelecteditemtemplateHTML

</SelectedItemTemplate>

<SeparatorTemplate>SeparatortemplateHTML

</SeparatorTemplate>

<FooterTemplate>

FootertemplateHTML

</FooterTemplate></asp:DataList>ThecustomtemplatesyoucreatetodisplaythedatacancontainbothHTMLtraditional elements(suchas<b>,<table>,<select>tags)andanyofthecontrolsthatwere discussedinthissection.Thinkoftemplatesaswrappersforpresentationforcertainsectionsofthecode.TheDataListcontrolsupportsthetemplatesshownin Table35 - 5 .Table35-5:TemplatesUsedintheDataListControl

Template DescriptionItemTemplate Thisistheonlyrequired template.The ItemTemplateisrendered

onetimeforeachrowof data.

AlternatingItemTemplate Ifthistemplateisprovided withintheDataList control,itrendersforevery otherrowofdata.Usethis templateifyouwanttoprovidealternatingcolorsfortherowsofyourtable.

SelectedItemTemplate Thistemplatedisplayswhen theuserselectsanitemthatisintheItemTemplateor the AlternatingItemTempla te.Youcanchangethe backgroundcolororeven showadditionalinformation

Table35-5:TemplatesUsedintheDataListControl

Template DescriptionEditItemTemplate Thetemplatethatis displayedwhentheuseris editingoneoftherowsof data.

HeaderTemplate Ifthistemplateisprovided, itisthefirstrowbeforethe ItemTemplateis rendered.Youcandisplay columnheadingsand introductionswiththis template.

FooterTemplate Similartothe HeaderTemplate, althoughthisisthelastrow afterallthedatais displayed.

SeparatorTemplate Thistemplateisrendered betweeneach ItemTemplateor AlternatingItemTempla te.Itisusefultoprovide somesortofvisual separationofrowsofdata.Inoneofitssimplerforms, theSeparatorTemplate cancontainjustan<hr>tag.

Figure35-17: TheMicrosoftAccessCustomerstableinDesignview

Chapter36:ValidationControlsIntroductiontoValidationcontrolsHowtouseValidationcontrolswithinWebFormsHowtouseregularexpressions

What Validation MeansValidationistestingtodeterminewhethertheuserenteredsomethingintothefield.Afteryoudeterminethatsomethingwasentered,youcanalsochecktoseewhetherwhatwas enteredis eithera numberora character,andalsocompareuserinputbetweendifferent fields.

DatacollectionontheInternetisoneofthemostimportantfeaturesavailable,anditis importanttomakesurethatthedatayoucollecthasvalueandmeaning.Thewaytodo thisistomakesurethatyoueliminateanychancesthattheinformationcollecteddoes notabidebytherulesyououtline.

Thevalidationcontrolsatyourdisposalincludethefollowing:CompareValidatorCustomValidatorRangeValidatorRegularExpressionValidatorRequiredFieldValidator

ValidationSummary

Table36-1:ValidationControls

ValidationControl Description<asp:comparevalidator> AValidation controlthat allowsfor comparison sbetween theuser's

inputandanotheritemusinga comparison operator (equals, greater than,lessthan,andsoon).

<asp:customvalidator> AValidation controlthat checksthe user'sentry using custom- coded validation logic.

<asp:rangevalidator> AValidation controlthat checksthe user'sinput basedupon alower-and upper-level rangeof numbersor characters.

<asp:regularexpressionvalidator> AValidation controlthat checksthat theuser'sentry matchesa pattern

definedbya regular expression. Thisisa goodcontrol touseto checke-mail addresses andphone numbers.

Table36-1:ValidationControls

ValidationControl Description<asp:requiredfieldvalidator> AValidation controlthat ensuresthat theuserdoesnotskipaform

entryfield.

<asp:validationsummary> AValidation controlthat displaysall theerror messages fromthe validatorsin onespecific spotonthe page.

Figure36-1: TheformwithoutanyvalidationPlacethiscontrolrightunderthebanneroftheform.Testit,andnoticehowitis displayingthepageerrors.FeelfreetoswitchtheDisplaymodetobothListand Paragraphtoseehowitlaysout.Also,anothergreatfeatureofthiscontrolisthatitcan displaytheerrorsinapop-upmessageboxforLevel4browsersandabove.

Chapter38:EventsAneventoccurswhenanobjectonthepagesendsamessagetotheserverthatsome sortofactionhastakenplace.Understandingevent-drivenprogrammingisessentialto programmingVisualBasic.NETWebapplications.VisualBasic.NETisbuiltonthis principlethatthepageyoudevelopisfullofobjects,andtheseobjectssometimesreact toeventsfromtheuser,systemevents,orothereventsyouprogram.

PlacingEventsinYourControlsControlsareobjectsthatwaitforspecificeventsandnotifytheserverwhen thosespecifiedeventstakeplace.Theactthatinitiatesthenotificationiscalled atrigger,andtheobjectthatsendsthetriggeriscalledaneventsender.The codethatrunswhenaneventistriggerediscalledaneventhandler.Acommonexampleofanobjecttriggeringaneventisabuttononapage.Thebuttonistheobject,andtheuserclickingonitinitiatesthetrigger(theOnClickevent)thatisthensenttotheappropriateeventhandler.Forinstance,<asp:button>allowsthefollowingevents tobeused:

OnClickOnCommandOnDataBindingOnDisposedOnInitOnLoadOnPrerenderOnUnloadIntelliSensedisplayslightning-bolticonsnexttoevents,asshowninFigure3 8 - 1.

Figure38-1: IntelliSenseshowingtheavailableeventsfortheButtonWebcontrol

Table38-1:EventArguments

Parameters DescriptionsenderAsObject Anobject that represents theobject thatraised theevent.

Table38-2:OtherTypesofArguments

EventArgs(System.TypeName)

DescriptionFileSystemEventArgs Provides information ondirectory events,such as Created, Changed, and

Deleted.ImageClickEventArgs Provides information onwhena userclicks on an image.

KeyEventArgs Provides information onkeyboard events,such asKeyUp and KeyDown.

CommandEventArgs Provides information onthe command event.

Building EventsAfteryou'vespecifiedtheeventwithinthecontrol,youneedtogivetheevent callavalue.Thisvaluewillbethenameoftheeventhandlerforthatparticular event.Forinstance,ifyouwantedthebuttontomonitorclickevents,youwould usetheOnClickeventandthenmaketheeventhandler,Button1_Click, performthefunctionalityyouwantedbasedonthatevent.

Thesampleeventhandlerhasthefollowingformat:

SubButton1_Click(SenderAsObject,EAsEventArgs)

Button1.Text="Thebuttontexthaschanged!"

EndSub

Using Web Form EventsEventsinWebFormsareconsiderablydifferentthaneventswithindesktopapplications. Withinatypicaldesktopapplication,theevent'striggerandtheeventhandlerareboth happeningclient-side.EventswithinaWebFormaretriggeredclient-side,butinmost casestheyneedtobehandledontheserver.ASP.NETusesHTTPPosttomanage theseserver-sideevent-handlingsituations.TheASP.NETframeworkthendetermines whichmethodneedstotakecareofhandlingtheevent.

ASP.NETtakescareofallofthisforyoubehindthescenes,butit'simportantto understandwhat'sgoingonhere.SinceWebapplicationsneedtomakeround-tripsto theservertoperformserver-sideevents,usingalargenumberofservercontrolsthat containasubstantialnumberofserver-sideeventscanhaveadefiniteimpactonthe performanceofyourWebapplication.

EventargumentsTheeventhandlersthatyoubuildforWebFormapplicationscontaintwoarguments, senderAsObjectandeAsEventArgs.Table38 - 1 describesthesetwo arguments.

Table38-1:EventArguments

Parameters DescriptioneAsEventArgs Containsall theevent specificdata thattheeventsender passes along.

Inmostcases,thesetwoargumentswillbethetypicalargumentsusedwithinanyeventhandler.ThesecondargumentwilltypicallyusethetypeSystem.EventArgs,butthere arecertaincontrolsthatrequireaspecifictypetopassalonganydatapertinenttothe controlthat'ssendingtheevent.Table3 8 - 2 listssomeotherpossibletypesofarguments thatyoucanuseinplaceofEventArgs.

Table38-2:OtherTypesofArguments

EventArgs(System.TypeName)

DescriptionFileSystemEventArgs Provides information ondirectory events,such as Created, Changed, and

Deleted.ImageClickEventArgs Provides information onwhena userclicks on an image.

KeyEventArgs Provides information onkeyboard events,such asKeyUp and KeyDown.

CommandEventArgs Provides information onthe command event.

EventpostbacksWhenyou'reusingHTMLandWebcontrolsthroughoutyourpages,therearemany eventtriggersthatcauseaneventtobesenttotheservertobehandled.Forinstance, thebuttonOnClickissenttotheserverforprocessingoncetheuserclicksonthe button.However,therearealsoeventsthataretriggeredonaWebFormthatare depositedandsaveduntilthere'sapostbacktotheserverforprocessing.

Creating Event Handlers in Design Mode

Defaulteventhandlers

Followthesestepstocreateanapplicationthatallowsyoutobuildeventsforthebutton control.1. StartanewapplicationcalledEventHandlerApp.Thiswillbean

ASP.NETWebapplication.Onthepage,placeabuttonandalabel control.Figure3 8 - 3showswhatyourpageshouldlooklike.

Figure38-3: YourWebForm1.aspxpage2. Double-clickontheButtoncontroltocreateapagecalled

WebForm1.aspx.vb.Withinthispage,yourcursorwillbeplacedwithin afreshlycreatedeventhandler,abuttonclickhandler.Yourpage shouldresembleFigure 38 - 4 .

Figure38-4: WebForm1.aspx.vbandyourButton1_ClickeventhandlerVisualStudio.NETchosetheclickeventhandlerforthebuttonbecausethat's theButtoncontrol'sdefaultevent.Eachcontrolhasitsowndefaultevent.For instance,theDropDownListcontrol'sdefaulteventisthe SelectedIndexChangedevent.

3. Next,addthefollowingcodefortheButton1_Clickevent:

Label1.Text="Thebuttonhasbeenclicked!"Whenyouright-clickonWebForm1.aspxwithintheSolutionExplorerand selectBuildandBrowse,you'representedwiththenewlycreatedpage.

4. ClickthebuttonandyougetthetextwithintheLabelcontrolthat informsyouthatyouclickedthebutton,initiatinganevent.Thiswasall basedupontheeventhandlerexecutingcodebaseduponatrigger(thebuttonclick).TheresultcanbeseeninFigure38 - 5 .

Figure38-5: Youreventhandlerinaction!

Non-defaulteventhandlers

WhatifyouwanttoaddmoreeventhandlersbaseduponyourButtoncontrol?VisualStudio.NETmakesitquiteeasy.Simplyfollowthesesteps:

1. Getbacktothecode-behindpagebyclickingonthe WebForm1.aspx.vbfiletab.Therearetwodrop-downboxesatthe topofthepage.TheoneontheleftistheClassNamedrop-downbox. TheotheristheMethodNamedrop-downbox.

TheClassNamedrop-downboxcontainsalistofthecontrolsthatareonthepage.Byselectingoneofthecontrols,youcanspecifyspecificevent handlersfortheselectedcontrol.

2. SelecttheButton1control,andthenyoucanpulldownalargelistof eventsyoucanuseagainsttheButtoncontrolwithintheMethodName drop-downbox.Thedefaultevent,Click,isinbold.Youshouldseea listofevents,asshowninFigure38 - 6 .

Figure38-6: Alistofavailableeventstoprogramagainst3. SelecttheLoadevent.Thesubroutineforthiseventisthencreated instantlyinthecode-

behindpage,withtheproperarguments.4. Addthefollowingcode:

Label1.Text="Thebuttonhasloaded!"5. Right-clickonthefileandchooseBuildandBrowse.Noticethatonce

theButtoncontrolisloaded,itdisplayswhatithadintheLabelcontrol. PressingthebuttonchangesthetextwithintheLabelcontrolbased upontheButton1_Clickevent.TheresultscanbeseeninFigure38 - 7 .

Figure38-7: Whenthepageisloaded,theButton1_Loadeventistriggered.

VisualStudio.NETletsyouprogramforyourcontrol'sdefaulteventsaswellasthenon- defaultevents,asyoujustdidinthepreviousexample.

Chapter40:StateManagement

Understanding StateTraditionalWin32applicationsconsistentlymaintainedstateastheuserworkedthrough theprogram.Thestateoftheuserwasconsistentlyknowntotheapplication.Basically, stateiswhattheapplicationknowsabouttheuser.Thatincludeswhotheuseris,where heisintheprocessoftheapplication,andwhathehasenteredintotheapplicationto thatpoint.

ASP.NETincludesthefollowingfeaturesandtechniquestoapplywhenyou'reworking withstatemanagement:ViewStateQuerystringsSessionsCookies

ViewStateViewStateisthelatestASP.NETfeaturethatwasn'tavailableinASP3.0.With ViewState,youcaneasilymaintainthestateofyourcontrolsbetweenroundtripstothe server.ASP.NETrequiredthiscapabilitybecauseyoucanprogramyourWebformswith multipleroundtripstotheserver.It'spossibletoprogramyourWebcontrolssothateach controlforcesthepagetomakearoundtriptotheservereverytimethecontrolis changedinordertoperformanevent.

TogglingViewStateonandoff

KeepingtheViewStatefunctionalityonisn'talwaysgoingtobeaprioritywitheveryWeb formyoucreate.Forthisreason,youcanturntheViewStateoff,thussavingserver resourcesandincreasingthespeedofyourapplication.Youcanturnthisfunctionalityoff

intwoways.ThefirstistodisableViewStateonthepagelevel,andtheotheristodisableitonthecontrollevel.TodisableViewStatefortheentirepage,turnoffthisfunctionalitywithinthepagedirective.ToturnofftheViewStatefunctionalityfortheentirepage,justaddthefollowingattribute tothepagedirectiveatthetopofthepage.

<%@PageEnableViewState="False" %>It'salsopossibletodisableViewStateonthecontrollevel.Ifmaintainingacontrol'sstate isnotanimportantfeatureofthatcontrol,turnitoff.Thismildlyincreasesthe performanceofthepageoverall.ToturnoffViewStateforacontrol,addthe EnableViewStateattributetothecontrol:

<asp:Labelid="Label1"Runat="Server" EnableViewState="False"

/>Tip PayingattentiontowhichpagesandcontrolsareViewState-enabled

leadstobetteroverallapplicationperformance.

QuerystringsQuerystringsareaneasywaytopassdatafromonepagetothenextwithinaWeb application.Theyplaceacreatedname/valuepairandappenditontotheURLtobe passedtothenextpage.

Creatingquerystrings

Thereareanumberofdifferentwaystocreatequerystrings.Oneofthesimplerwaysis todirectlyplacethename/valuepairswiththeURL.

<ahref="WebForm2.aspx?username=Bill&employeeid=9040777>RegistrationPage</a>

WhereverthereisaURLinyourpage,youcanplacequerystringsalongwiththatURL. Forexample,youcanworkthemintoyoureventsonthecode-behindpageasfollows:

Response.Redirect("WebForm2.aspx?username=Bill")

It'salsopossibletocreatethevaluesofthequerystringsasthepageisparsedonthe serverbyconcatenatingthevaluestotheURL:

Response.Redirect("WebForm2.aspx?user="&TextBox1.Text&_

"&employeeid="&TextBox2.Text&"")

CookiesCookiesarekey/valuepairsthatarestoredontheclientcomputer.Usingcookiesto persistinformationisasimpleandeasyoptioninASP.NET.Cookiesarepassedalong withtheHTTPrequesttotheserverandareusedtoidentifytheuseruponreceipt.

Advantagestousingcookies

Therearemanyadvantagestousingcookieswithinyourapplicationstostoresimple data.Firstofall,itdoesn'trequireserverresourcesbecausenoneofthecookiesare storedontheserver.Secondly,youcansetcookiestoexpirewhenthebrowserisshut downorforanydateinthefuture.Therefore,it'spossibletoremembertheuserupon returnvisitsweeksormonthslater.

Disadvantagestousingcookies

Therearealsosomenegativestousingcookies,andforsomeapplicationstheycan accountforsomeserioussecurityflaws.Onenegativeisthatcookiesneedtobesmall. Youcannotsendlargeamountsofdatatotheclienttostoreontheirmachine.Generally, there'sa4,096-bytelimittothesizeofacookie,sothetypesofdatathatyoucanstore arelimited.Thebiggestnegativeisthatcookiesareeasyforknowledgeableusersto change.Thiscanbeamajorproblemifyou'reusingcookiesforuserstogainaccessto privateinformation.

Chapter41:ASP.NETApplicationsAWebapplicationmayconsistofacollectionofASP.NETfilesandtheGlobal.asax file.(TheGlobal.asaxfileisdiscussedinitsownsectionofthischapter.)Whenyou typeaURLintoyourbrowser(suchashttp://www.somewhere.com/), you'recalling aWebapplicationandfiringanyapplicationeventsthatgoalongwithit.Locallyonthe server,theWebapplicationresidesinavirtualdirectorythatyouspecify,typicallywithin theC:\Inetpub\wwwrootdirectory.

Creating a Web ApplicationWithclassicASP,youcouldcreateaWebapplicationbyhavingacollectionof.aspfilesandaglobal.asafilewithintherootdirectory.It'simportantto notethattheseclassicfilescanresideinthesamevirtualdirectoryasyour.aspxpageswiththeglobal.asaxfileandtheywon'tinterferewitheachother.Thesetwoapplicationswon'tsharestateorevents.Intheusualfashion, whenpeopleupgradefromoneversionofaproducttoanother,thenewversionususallyoverridestheolderone.Butinthiscase,ASP.NETdoesn't overridetheclassicASPdynamiclinklibrary(DLL).Instead,filesrunside-by- side.However,interminglingthetwomayproveproblematicbecausethetwo versionsdon'tsharestateorevents.

WiththegrowthoftheInternetandthewideacceptanceoftheWebbrowseras awaytoportinformationandapplicationsaroundtheworld,moreandmore emphasisisbeingplaceduponWebapplications.It'snowbecomingastronger necessityindevelopmenttomakeagroupofpagesworktogetherjustasa groupofformscanworktogetherinaWin32application.Theincreasing popularityoftheInternetasaportalforWebapplicationdevelopmentisdirectly relatedtothegrowthoftheInternetasawhole.Itisbecomingfareasierfor companiesandorganizationstouseabrowsertoporttheirapplications,insteadofforcinguserstoinstallacertainversionofanapplicationontheir machinesathomeoratwork.Portingtheirapplicationsthroughthebrowser guaranteesusersthelatestversionoftheapplication.Usersarealsoquite knowledgeablethesedaysaboutworkinginformsthatareinabrowser.Itis alsofarbetternottoworryabouttheenduser'shardwaresituationandpush thedata,asopposedtopullingdatainaWin32application.ProbablythebiggestconcernwithWebapplicationdevelopmentfor programmersisstatemanagementortheapplications'abilitytopassthevalue ofvariablesfromonepagetoanother.Howyouhandlethismatteralso addressesissueswithsecurityandserverresources.

WithVisualStudio.NET,creatingaWebapplicationisaneasyand straightforwardprocess.Todoso,followthesesteps:

1. FromtheStartPagethat'sdisplayedwhenyoupullupVisualStudio.NETforthefirsttime,openanyexistingapplicationsthatyou've createdinthepast,orstartanewapplication.Ifyoudonotseethe StartPagewhenyouopenupVisualStudio.NET,clickHelpShowStartPage.TheStartPageisshowninFigure 41 - 1 .

Figure41-1: StartanewapplicationinVisualStudio.NETfromtheStartPageandselectNewProject.

2. Tostartanewapplication,clickontheNewProjectbutton.This displaysthedialogboxyouseeinFigure4 1 - 2 .Ithasalargelistof variousapplicationsthatyoucancreatewithVisualStudio.NET.

Figure41-2: NewProjectdialogbox.3. ChooseASP.NETWebApplicationandclickOK.VisualStudio

.NETautomaticallycreatestheapplicationforyou,aswellasthe appropriateapplicationfiles(suchasglobal.asax).AfterVisual Studio.NETcreatestheapplication,youcanseeallthefilesinthe SolutionExplorerwindow(seeFigure41 - 3 )withinVisualStudio.NET,oryoucanviewthefilesinyourC:\Inetpub\wwwroot\directoryonthelocalserver.

Table41-1:Application-SpecificItems

ItemCreated Description\binFolder Thisfolderisusedfor.NETassembliesthatareusedby

theapplication.Global.asax Thisisafilewhereyoucanspecifyapplicationeventsand

variables.ThisisthenextversionoftheclassicASP global.asafile.

web.config ThisisanXMLfilethatallowsthedevelopertoset applicationsettingssuchassecurity,state,andanumber ofotheritems.

Figure41-3: TheSolutionExplorerdisplaystheentireWeb applicationyou'vecreated.

Noticethatbycreatingthisapplication,you'vecreatedanumberof otheritemsaswell.NotalltheitemsareshownintheSolution Exploreratthispoint,though.

4. LookatthefilesthatarelistedintheSolutionExplorer,andthengotoC:\Inetpub\wwwroot\WebApplication1andcompare what'sdifferent.Therearesomeextrafilesandfoldersinthe WindowsExplorerview.VisualStudio.NETdoesn'tshowyouallthe filesthatareactuallywithintheapplication,butonlytheonesthat youneedtoworkwithonaregularbasis.

5. ToshowmoreofthefilesandfoldersthatareatyourdisposalwithintheSolutionExplorer,clickontheShowAllFilesbuttonlocatedat thetop.Thisshowsalargerlistofavailableitems.Themost importantoftheseapplicationitemsaredescribedin Table41 - 1 .

Deleting an ApplicationDeletingordestroyinganapplicationisjustaseasyascreatingitwas.Withinthe SolutionExplorerwindowinVisualStudio.NET,right-clickontheapplicationandselect Remove.Thisremovestheapplicationfromtheserveranddeletesallthefiles.

global.asaxTheglobal.asaxfileisusedbytheapplicationtoholdapplication-levelevents, objects,andvariables.It'sthenextversionoftheglobal.asafilethatwasusedin classicASP3.0,soifyouwerecomfortablewiththat,you'llfeelquiteathomewith global.asax.

Therecanonlybeoneglobal.asaxfileforanapplication.However,it'spossiblefora global.asaxfiletoresidenexttoaglobal.asafilewithoutanyconcerns.Just realizethatrunningthemside-by-sidewon'tallowyoutosharesessionsorevents betweenthetwo.Inthissituation,your.asppageswithintheapplicationusethe global.asafile,andthe.aspxpagesuseitsapplicationfile,global.asax.Theglobal.asaxfilesupportsanumberofitems:

Directives—VerymuchlikethedirectivesthatareusedinASP.NETpages, usercontrols,andWebServices,thesedirectivesallowyoutospecify instructionstotheapplication.

Declarations—Theseallowyoutodeclarespecificitemssuchasscriptsandincludes.

Applicationevents—Theseareeventsthatcanbeinitiatedonanapplication level.

ApplicationdirectivesApplicationdirectivesareverymuchlikethedirectivesthatyoucanusewithinASP.NET pagesandWebServices.Theglobal.asaxfilesupportsthethreefollowingtypesof directives:

@Application @Import @Assembly

Beforeexploringeachofthese,it'simportantthatyouunderstandhowtowritean applicationdirectivewithinyourglobal.asaxfile.Thedirectiveiswritteninthe followingformat:

<%@[Directive][Attribute=Value]%>Thedirectivegoesatthetopofthepageintheglobal.asaxdocument.Thedirective isopenedandclosedwiththesamebracketsusedinclassicASP,withtheopening<% andclosing%>.Thedirectiveallowsforasmanyattribute/valuepairsasyouwish.Soif youhadmorethanoneattribute,thedirectivewouldbewrittenasfollows:

<%@[Directive][Attribute=Value][Attribute=Value]%>

@ApplicationThe@Applicationdirectivedefinesapplication-specificattributes.Thisdirective supportsthetwofollowingtypesofattributes:

Inheritsallowsdeveloperstospecifythebaseclassthatglobal.asaxuses.

Descriptionallowsdeveloperstospecifyadescriptionfortheentireglobal.asaxfile.

Here'sanexamplethatusesbothattributeswithinonedirective:

<%@ApplicationInherits="PM.Object"Description="TheProject

ManagementApplicationfortheSalesDepartment."%>Note TheASP.NETparserignoresthedescriptiondirectiveatruntime.

Thisisimportantifyouhavealengthydescription.

@ImportThe@Importdirectivespecifiesthenamespacestobeimportedintotheapplication, therebymakingallclassesandinterfacesavailabletothepagesoftheapplication.This directiveonlysupportsoneattribute—Namespace.TheNamespaceattributedirectlyspecifiesthenamespacetobeimported.Notethatwith the@Importdirective,itcannotcontainmorethanoneattribute/valuepair.Here'sanexamplethatimportstwodifferentnamespacesusingthe@Importdirective:

<%@ImportNamespace="System.Data" %>

<%@ImportNamespace="System.Net" %>Theimportantthingtounderstandisthattherearealreadyanumberofnamespaces beingimportedintotheapplicationautomatically.Thefollowingnamespacesarealready imported:

System System.Collections System.Collections.Specialized System.Configuration System.IO System.Text System.Text.RegularExpressions System.Web System.Web.Caching System.Web.Security System.Web.SessionState System.Web.UI System.Web.UI.HtmlControls System.Web.UI.WebControls

There'snoneedtore-importtheseitemsbecausethey'realreadythere.It'salsopossible toimportnamespacesintoyourapplicationswithintheweb.configfile,whichare discussedlaterinthechapter.Importinganamespaceintoyourapplicationallowsyoutouseitsclasseswithoutfullyidentifyingtheirnames.Forinstance,ifyouimportthenamespaceSystem. Data.OleDBintotheapplicationorintotheASP.NETpage,youcanthenreferto

classeswithinthisnamespacebyjustexpressingthesingularclassnames.Youcould refertoOLEDBConnectioninsteadofSystem.Data.OleDB.OLEDBConnection,for example.

@AssemblyThe@Assemblydirectiveattachesassembliestoapageasitcompiles,thereby makingalltheassembly'sclassesandinterfacesavailabletothepage.Thisdirective supportsthetwofollowingattributes:

Nameallowsdeveloperstospecifythenameofanassembly.Thisassemblyistheonethatisattachedtothepagefiles.Thenameofthe assemblyshouldonlyincludethefilenameandnotthefile'sextension. Forinstance,ifthefileisMyAssembly.vb,thevalueofthename attributecouldbeMyAssembly.

Srcallowsdeveloperstospecifythesourceoftheassemblyfiletouse incompilation.Note TheSrc(source)attributeisanoptionalattributethatspecifiesthe

fileofthecodethatyouwanttoincludewithinthescriptblock.Anexampleofthe@Assemblydirectiveisasfollows:

<%@AssemblyName="MyAssembly"%>

<%@AssemblySrc="MyAssembly.vb"%>Notethatthesourceattributecancontainthecompletepathaswell.Also,any assembliesthatareplacedwithinthe\bindirectoryareautomaticallyavailabletothe page.

DeclarationsCodedeclarationswithinaglobal.asaxfileworkinthesamemannerastheydowithinyourASP.NETpages.Codeisdeclaredbetween<script></script>tags,and youcandefineanynumberofvariables,eventhandlers,andmethods.Hereisan exampleofusingcodedeclaration:

<scriptrunat="server"language="LanguageType" src="FilePath">

Writeyourcodeouthere.

</script>The<script>tagmustcontainarunat=serverattribute/valuepair,andthenyoucanspecifytwootherattributeswithinthetagitself—thelanguageandsrcattributes.Thelanguageattributespecifiesthelanguagethatisusedinthescript.Forthepurposesofthisexercise,usethelanguage="VB"attribute/valuepair.Youdon'tneedtodeclarethisattributewithinthe<script>tagifyou'vedeclaredthelanguageineithertheapplicationorpagedirective,orifit'sdeclaredintheweb.configfile.Thefollowingcodedemonstrateshowtousethe<script>tagswithinaglobal.asaxfiletodefineaneventhandler:

<scriptlanguage="VB"runat=server>SubApplication_OnStart()

'Applicationstartupcodegoeshere…

EndSub

</script>

Understandingweb.configweb.configisanapplicationfilethatallowsyoutosetapplication-widesettingsfrom oneconvenientfile.Thisfileiscreatedforyouwhenyoucreateanapplication.Ifyou wantedtochangeanyoftheapplicationsettingsinclassicASP,itwasdoneintheIIS MicrosoftManagementConsole(MMC).Theadministratorhadtostopandstartyour applicationforthesettingstotakeplace.WithASP.NET,youjustneedtoopenthe web.configfileinanytexteditor,changethesettings,andresavethefile.ASP.NET canthendetectwhentherearenewconfigurationsettingsforyourapplication,andit doesn'tneedtostopandstarttheapplication.Instead,ASP.NETletscurrentusersfinish withtheapplicationundertheoldsettings,andanynewusersaredirectedtothe applicationwiththenewsettingsapplied.

Chapter42:TracingAgreatnewfeatureofASP.NETistheabilitytotracetheinformationthat'spassedfrom requestsandresponses.Thisplaysagreatroleintheerror-checkinganddebuggingof applications.

ThetracingfeatureinASP.NETisanewmeansofdebuggingaWebapplication.Oneof themoreimportantstepsindevelopingapplicationsfortheWebisunderstandingwhich

informationisbeingsentfromonepagerequesttothenext.Withtracingturnedonin yourASP.NETapplication-youcancloselyfollowallthevariablesandconditionswithin yourpagesinunprecedentedways.

Understanding the Benefits of ASP.NET Tracing Everyonemakesmistakes,andprogrammersarenoexception.These mistakescouldbeinthecode,orhowthebrowserinterpretsthecode.Theycouldevenbeinthecommunicationsbetweencomponents.ClassicASPdidn't allowdeveloperstoeasilytraceinformationinrequestsandresponses.So instead,manydevelopersbuilttheirowntypesoftracingdirectlyintothecode. Forexample,manyprogrammerswouldlittertheirapplicationswith Response.Writestatementstoseehowtheirpage'sstatewasworking.Note Response.Writeisameansofwritingcontenttothebrowser

window.Forexample,writingResponse.Write("ASP.NET iscool!") causesthespecifiedtexttobeprintedtothebrowserwhenthe usercallsthepage.

Carryingsessionsaroundfrompagetopage,andinmanycaseschangingthevalueofthesesessions,isvitaltotheproperfunctioningofyourapplications. Therefore,placingtheseResponse.Writestatementsalloweddevelopersto seewhatwashappeningwiththesessionsandotherelementsasthey progressedthroughtheapplication.Althoughthisworked,thereweremanyproblems.Ittooktimetoplacethesestatementsintheapplicationonthe pagesthatneededthem.Then,ittooktimetoeithercommentthemalloutor removethemfromtheapplicationaltogether.

Enabling TracingYoucanconfigureyourASP.NETapplicationstoenabletracingintwoplaces.Thefirstis attheapplicationlevel,andthesecondoptionisatthepagelevel.Notethatyoucanhavebothoptionsturnedonatonce.

EnablingtracingattheapplicationlevelIt'squiteeasytoenabletracingwithinyourASP.NETapplicationsateithertheapplicationlevelorthepagelevel.Toenabletracingapplication-wide,opentheweb.configfileandmakesomemodificationsthere.Youcanfindtheweb.configfilewithintherootofyourapplication.

.

Table42-1:Attributesinthe<trace>Node

Attribute DescriptionEnabled Turnsthe tracingonoroff. Thedefaultis false.

RequestLimit Thisisthe numberof HTTPrequests thatwillbe recorded.The defaultsettingis 10.Asthe requestsbuild up,ASP.NET tracingkeeps trackofthelast specified numberof requests.

Whenyouopentheweb.configfile,youseethefollowinglineofcodethatdealswith tracingintheapplication:

<traceenabled="false"requestLimit="10"pageOutput="false"

traceMode="SortByTime"localOnly="true"/>Toturntracingon,changetheenabledattributetotrue.Thisturnstracingon,but

nothingisviewableonthepagesthemselvesyet.Table4 2 - 1 listswhattheseattributes meaninthemodificationofthetracingenvironment.

Table42-1:Attributesinthe<trace>Node

Attribute DescriptionPageOutput Asettingoftrue meansthatthe tracing informationis shownoneach pageasit's

rendered,in additiontobeingrecordedinthe trace.axdfile. Thedefaultis false.

TraceMode Thisattribute specifiesthe displayorderof thetracing information. Optionsinclude SortByTimeor SortByCatego ry. SortByTimeis thedefault setting.

LocalOnly Indicates whetherthe trace informationis shownonlyon thelocalserver orisshownto remoteclients also.

Chapter43:SecurityAuthentication and AuthorizationThewaytomakesecurityworkinyourapplicationsiswithauthenticationand authorization.Eachoneplaysanimportantroleinthedevelopmentofthesecuritymodel thatyoubuildintoyoursite.

AuthenticationAuthenticationistheprocessofdeterminingtheidentityoftheuser.Oncetheuserhas beenauthenticated-youcanusehisidentitytodetermineifhehasauthorizationto proceed.

Therearemanydifferentmodesofauthenticationtousewithinyourapplications.Someofthesemodesincludebasicauthentication-digestauthentication- formsauthentication- Passport-IntegratedWindowsauthentication(suchasNTLMorKerberos)-or authenticationmethodsthatyoumightdevelopyourself.

Theweb.configfilehasthreedifferentauthenticationmodulesthatyoucanuseinthe developmentofyourWebapplications:

Windows Forms Passport

Table4 3 - 1 describesthedifferencesintheseformsofauthentication.Table43-1:AuthenticationProviders

AuthenticationProvid

Description

Windows Windows authenticati onisused together withIIS authentication.Authenticationis performed byIISinthe followingways:basic- digest-or Integrated Windows Authenticati on.WhenIIS authenticati onis complete- ASP.NET usesthe authenticate didentityto authorize access.

Forms Requests thatarenot authenticatedrequests are redirectedto anHTML formusingHTTPclient- side redirection. Theuser provideshis login information andsubmits theform.If the application authenticatestherequest-thesystem issuesa formthat containsthe credentialsora keyfor reacquiring theidentity.

Table43-1:AuthenticationProviders

AuthenticationProvid

Description

Passport A centralized authenticati onservice providedby Microsoft thatoffersa singlelogin andcore profile servicesfor member sites.

<authenticationmode="Windows|Forms|Passport|None"/>

Noticethatfourpossiblechoicesareusedindeterminingthemodeofauthentication. ThedefaultsettingisWindows.

Windows-basedauthenticationWindows-basedauthenticationexistsbetweentheWindowsserverandtheclient's browser.Windows-basedauthenticationgoestoIIStoprovidetheauthentication module.Usingthiskindofauthenticationisquiteusefulinanintranetenvironment- whereyoucanlettheserverdealwiththeauthenticationprocess.

Windows-basedauthenticationfirsttriestousetheuser'scredentialsfromthedomain login.Ifthisfails-itthenpopsupadialogboxsotheusercanre-enterhislogin information.WhenWindows-basedauthenticationisused-theuser'spasswordisn't passedfromtheclienttotheserver.Ifauserhasloggedonasadomainuseronalocal computer-theuserwon'tneedtobeauthenticatedagainwhenaccessinganetwork computerinthatdomain.ThenextstepistoconfigurethesampleapplicationsothatitusesaWindows–basedauthenticationsystem.

CreatingusersFollowthesestepstocreateusersonthelocalserver:

1.WithinWindows2000Professional- openuptheComputerManagementutility(Start ControlPanel AdministrativeTools

ComputerManagement).Youcanalsoopenuptheutilityby right-clickingontheMyComputericononyourdesktopand choosingManage.

Note TheComputerManagementutilitymanagesandcontrolsresourcesonthelocalorremoteservers.Therearemanythingsthatyoucando withintheComputerManagementutility-butyouwanttofocuson creatingusers.OpenuptheLocalUsersandGroupsbranch.

2.Afterexpandingthisbranch-twofoldersaredisplayed-UsersandGroups.

3.Right-clickontheUsersfolderandselectNewUser-asshowninFigure43 - 1 .TheNewUserdialogboxappears(seeFigure 43 - 2 ).

Figure43-1: Selectinganewuser

Figure43-2: Givetheuseranameinthisdialogbox.4.Givetheuseraname-suchasJdoe.Youcanprovidehisfullname anddescription.5.GivetheuserapasswordandunchecktheUsermustchange

passwordatnextlogoncheckbox.Thisisjustatestonyourpart- butit'sbesttoforcetheusertodothiswhenyoucreatearealuser inthesystem.

6.Onceyou'vefilledinallthenecessaryinformation-clickCreate.YourusernowappearsinthelistofusersintheComputerManagement utility.

AuthenticatingandauthorizingauserNext-arrangeforIIStoauthenticateusersonceyouprovidetheauthorizationsbased upontheseauthentications.Inordertoaccomplishthis-openuptheweb.configfile andchangesomeoftheapplicationsettingswithinthefile.Youfindtheweb.configfile withintherootdirectoryofyourapplication.Onceit'sopen- navigatedowntothe<authentication>node.Directlyafterthisnode-placethefollowingcode:

<identityimpersonate="true"/>Itdoesn'tneedtobedirectlyafterthe<authentication>node-butit'sshownthat wayhereforfilereadability.They'rerelatedintermsofthefunctionalityyou'reworking withnow.Thiscodechangestheimpersonateattributetotruesothatyoudon'thavetodealwithauthenticationandauthorizationissuesintheASP.NETapplicationcode.Instead-you're relyingonIIStoeitherauthenticatetheuserandpassanauthenticatedtokentothe ASP.NETapplicationor-ifit'sunabletoauthenticatetheuser-passanunauthenticated token.Next-changethe<authorization>nodetosuityourneeds.Theauthorization elementallowsfortwosubelements-<allow>and<deny>.Youcanhaveasmanyof thesetwosubelementswithintheauthorizationelementasyouseefit.Boththe<allow>and<deny>nodescancontaintheattributesusers-roles-and verbs.usersspecifiesindividualuserstoallowordenyaccesstotheapplication- rolesisforgroups-andverbsspecifieshowtheusercametotheapplication.(Groups arediscussedinthenextsection .)Thischapterwon'tbeshowinganyexamplesusingtheverbsattribute-butbasically-youcanallowordenyusersbasedonwhethertheycametotheapplicationusingGET-POST-HEAD-orDEBUGmethods.

<authorization>

<denyusers="*"/>

</authorization>A"*"referstoallusers-anda"?"referstoanonymoususers.Soyoujustinstructed theapplicationtodenyallusers-evenifthey'reauthenticated.Next-typeintheURL.You'reaskedtologontotheapplication-eventhoughnobodyisallowed(seeFigure43 - 3 ).You'regiventhreechancestotypeinyourlogininformation.

Figure43-3: RequesttologontotheapplicationBecauseyou'renotlettinganyuseraccesstheapplicationafterthethirdtry-you're informedthatyouweredeniedaccess(seeFigure43 - 4 ).

Figure43-4: Accessdenied

Accessing Authentication PropertiesIt'spossibletoaccessauthenticationpropertiesandusethemwithinyourcode.For instance,directlyinthecode,it'spossibletoaccesstheuser'sloginnameandfindoutif he'sanauthenticateduser.

Tochecktheuser'sloginname,youwouldusethefollowingcode: DimUserNameAsString

UserName=User.Identity.Name

Tocheckiftheuserisauthenticated,usethefollowingcode: DimUserAuthAsBoolean

UserAuth=User.Identity.IsAuthenticatedThisreturnsTrueiftheuserisauthenticatedandFalseifhe'snot.Oneexampleistouse thisstatementdirectlyinanIfThenclause,asshownhere:

IfUser.Identity.IsAuthenticated Then

'dosomething

Else

'dosomethingelse

EndIfPerforming Forms-Based AuthenticationAnotherpopularwaytoauthenticateandauthorizeuserstohaveaccessto applicationresourcesistohavethemtypeintheircredentialsintoHTMLforms. Whenauserattemptstoentertheapplicationbutisunauthenticated,he's redirectedtoaspecifiedloginpage.Herehecantypeinhisusernameand passwordtogetauthenticated.Oncehe'sauthenticated,theuserreceivesa HTTPcookietouseonsubsequentrequests.Toactivateforms-basedauthentication,youfirstneedtochangetheweb.configfileasfollows:

<authenticationmode="Forms">

<formsname="MyForm"path="/"loginUrl="login.aspx"

protection="ALL"timeout="30">

<credentialspasswordFormat="Clear">

<username="Jdoe"password="Password"/>

<username="Bill"password="Obiwan"/>

</credentials>

</forms>

</authentication>

<authorization>

<allowusers="Jdoe,Bill"/>

<denyusers="?"/>

</authorization>Theattributesoftheformselementaredefinedasfollows:

name—Thisisthenamethatisassignedtothecookie.Thedefaultvalue is.ASPXAUTH.

loginUrl—SpecifiestheURLtowhichtherequestisredirectedfor loginifnovalidauthenticationcookieisfound.Thedefaultvalueis default.aspx.

protection—Specifiestheamountofprotectionyouwanttoapplytothecookie.Therearefouravailablesettings:All,None,Encryption,andValidation.

All—Specifiesthattheapplicationusesbothdatavalidationand encryptiontoprotectthecookie.Allisthedefault(and recommended)value.

None—Appliesnoencryptiontothecookie.Thisisn'tthebestsettingtouse,butitcouldbeusedforpersonalizationandforsettingsthatdon't requireanyamountoftruesecurity.Thisoptionistheleastresource- intensiveofthefourchoices.

Encryption—Thisisasettingwherethecookieisencryptedbutdata validationisn'tperformedonit.Cookiesusedinthiswaymightbe subjecttochosenplaintextattacks.

Validation—ThisistheoppositeofEncryption.Datavalidationisperformed,butthecookieisnotencrypted.

path—Specifiesthepathforcookiesissuedbytheapplication.Inmost casesyouwanttouse"/",whichisthedefaultsetting.

timeout—Specifiestheamountoftime,inminutes,afterwhichthe cookieexpires.Thedefaultvalueis30.

PartVII:WebServicesChapter44:IntroductiontoWebServices Chapter45:WebServicesInfrastructure Chapter46:SOAPChapter47:BuildingaWebServiceChapter48:DeployingandPublishingWebServicesChapter49:FindingWebServicesChapter50:ConsumingWebServices

Chapter44:Introduction to Web ServicesThe Next-Generation InternetThenextgenerationoftheInternetisuponus.Manytalentedandenergeticpeopleare workingveryhardtodelivertheinfrastructurethatwillmaketheInternetaplatformfor doingbusinessinwaysthatwereunimaginableonlyafewyearsago.ThisInternetofthe futureholdsgreatpotentialforallowingbusinessestocollaborateandintegratedataand applicationsasneverbefore.Itpromisestopulltogetherislandsofinformationintoa transparentlycoordinatedwholeanddeliverthatinformationtoallkindsofdevices, includingcellphones,personaldigitalassistants,handhelddevices,laptops,pagers,and others.Theheartandsoulofthesenext-generationservicesareExtensibleMarkupLanguage (XML),HypertextTransferProtocol(HTTP),andWebServices.XMLisaWorldWide WebConsortiumstandardthatpermitsdatatobeportableandself-describing,soitcan beexchangedeasilybetweenapplicationsanddevicesonmanyplatforms.Web ServicesallowuserstoprogrammaticallyexchangestructureddataencodedasXML overtheInternetviaHTTP.YoucanthinkofWebServicesasprogrammableURLs.

Statedanotherway,aWebServiceisanapplicationcomponentthatcanbecalled remotely.Thus,anysystemthatsupportsthesebasic,standardprotocolsiscapableof supportingWebServices.

Understanding the Need for Web ServicesWebServicessolveabasicbutpervasiveproblemthatmanyofusexperiencewith today'sInternet.Althoughthereareliterallybillionsofpagesofusefuldataand informationontheWeb,it'stypicallydifficulttoextract,examine,andusethatdata programmatically.MuchofthisdifficultyarisesfromthefactthattheWeb(atleastasitexiststoday)isdesignedforhumanconsumption.Consequently,dataispresentedinaformthat'seasyforpeopletoreadbutrelativelydifficultanderror-proneforapplications toreadandprocessreliably.

Asanexample,manye-commercesitesneedtocalculateshippingchargesbasedona varietyofshippingoptions.Typically,suchasitemightmaintainasetofdatabasetables thatdescribetheshippingoptionsandchargesforeachshippingcompany.Obviously, thiscanbecomeatime-consumingprocessbecausethedataislikelytochangeoften andsomeonemustupdatethetablesrepeatedly.Amoresophisticatedapproachmightincorporateaprocesscalledscreenscraping,whichanalyzesthedatainapageforcertainpatternsandextractsthisdataforfurther processing.SupposethatoneoftheshippingcompaniesmaintainsaWebsitethat convenientlyliststhevariousshippingoptionsandassociatedcharges.Byusingscreen scraping,aprogramcanexaminetheWebpageandextracttheshippinginformation fromthatpage.

Ofcourse,therearemanyotherpotentiallyvaluableapplicationsofWebServices.Some examplesoftheseservicesincludethefollowing:

Creditcardvalidation,financialaccountmanagement,stockquotes,and soon.Theseareservicesthatmightbetoodifficultortooexpensiveto implementyourself.

Userauthentication,usagebilling,usageauditing,andsoon.These servicesprovidecommonlyneededfunctionalityforotherservices.

Travelbooking.Thistypeofserviceaggregatesdistributed,discreteservices intoanorchestratedwhole.Accountsreceivable,accountspayable,invoicing,purchaseorders,and

soon.Theseservicesprovidetheabilitytointegrateyourbusiness systemswithyourpartners(orotherbusinesssystemswithinyourown organization).

Packagingapplicationcodeintoreusablecomponentsthatcanbecalledacrossprocess andmachineboundariesisn'tanewconcept.Today,wehavetechnologiessuchasthe ComponentObjectModel(COM),theCommonObjectRequestBrokerArchitecture (CORBA),InternetInter-ORBProtocol(IIOP)andRemoteMethodInvocation(RMI),to nameafew.Akeylimitationofthesetechnologiesisthatthey'renoteasilyinteroperable betweenthetremendousnumberofheterogeneoussystemsthatmakeuptheInternet.

Basic Elements of Web ServicesMicrosoftprovidesanexcellentplatformforbuildingandconsumingWebServiceswith the.NETFramework,whichvirtuallyeliminatestheneedtolearnaboutthe"plumbing" involvedinbuildingandconsumingWebServices.Ifthingsworkedrightallthetime,therewouldbenoneedtoevendiscussthisplumbing.Butofcourse,thingsdon'talways workright,soit'susefultohaveabasicunderstandingofthefoundationuponwhichWebServicesarebuilt.

Thekeytothebroad-reachingcapabilitiesofWebServicesontheInternetisasoftware infrastructurebuiltonInternetstandardsthatdoesn'trelyonanyplatform-specific technology.Thisinfrastructuresuppliesstandards-basedservicesthatprovidethe followingcapabilitiestoWebServices:

Describingdatainastructured,portablemannerCommunicatingrequestsandresponsesbymeansofanextensiblemessage formatDescribingthecapabilitiesofWebServicesDiscoveringavailableWebServicesDeterminingwhichsitesprovideWebServices

ThefollowingsectionswillhelpyoutounderstandwhytheseissuesareimportantandwillintroduceyoutothetechnologiesthatprovidethesecapabilitiestotheWebServices platform.

DescribingdataToenableWebServicestocommunicatetheirdataunambiguously,efficiently,and effectively,youmustuseacommon,portable,andstandardmethodfordescribingdata. Thesimple(andlogical)answerisXML.

XMLisusedextensivelyineveryaspectofWebServices.It'sastandards-basedmethod fordescribingdata(alsoknownasmetadata).XMLcandescribedatabyusingasimple grammarthatishighlyinteroperablebetweenthemanyhetero-geneoussystemsthatareconnectedtotheInternet.UsingthebasicelementsoftheXMLlanguage,youcandescribebothsimpleandcomplexdatatypesandrelationships.

XMLhasseveralkeystrengthsthathavehelpedittobecomethedefactomethodfor describingdata(especiallycomparedtoHTMLandotherbinaryformats).Theseinclude thefollowing:

It'satext-basedlanguage,whichmakesiteasilyreadableandmoreportablethanbinarydataformats.

Youcandefineyourowntagstodescribedataanditsrelationshipsto otherdata(hencetheword"extensible"initsname).

Itstrictlyenforcesitslanguagesyntax,unlikeHTML. ParsersarewidelyavailabletoaccuratelyparseandvalidateXML

structuresthatyoudefine,whichmeansyoudon'thavetodoityourself!

ThefollowingsectionsbrieflyexaminethesyntaxandstructureofXMLdocuments.

Specifically,whenyou'recreatinganXMLdocument,it'sveryimportantthatyoufollow thesebasicrules: Allelementsmusthaveanendtag. Allelementsmustbecleanlynested(nooverlapping). Allattributevaluesmustbeenclosedinquotationmarks. Eachdocumentmusthaveauniquefirstelement(thedocumentroot).

Chapter45:WebServicesInfrastructure

Microsoft WebServices PlatformOneoftheprimarymotivationsbehindthecreationoftheWebServicesarchitecturewas theinadequacyoftheexistingdistributedobjectmodeltechnologies,suchasthe DistributedComponentObjectModel(DCOM),theCommonObjectRequestBroker Architecture(CORBA),andtheInternetInter-OrbProtocol(IIOP)forInternet-based applications.Althougheachofthesetechnologiesworkedwellinacontrolled, homogeneousenvironment,thisobviouslycannotbeguaranteedforsystemsonthe Internet.What'smore,theselegacyobjecttechnologiescouldalsobeextremelylarge andcomplex(somemorethanothers).Again,thismakesitdifficulttorelyontheseolder technologiesasafoundationfordistributedcomputingontheInternet.

ThemajoradvantagesoftheWebServicesfoundationareitssimplicityanditsreliance onexisting(oremerging)Internetstandards.ThisensuresthatWebServicescanbe implementedallacrosstheInternet.AlthoughtheWebServicesfoundationdoesagreatjobofenablingaprogrammableInternetcomposedofdistributedbuildingblocks,there'sreallymuchmoretocreating scalable,robust,distributedapplications.Eachindividualplatformmustsupplythese servicesbecausetheWebServicesfoundationdoesn'tattempttoaddresstheseissues. TheMicrosoft.NETplatformisspecificallydesignedtoprovidetheseessentialservices thatmakeiteasytocreateworldclassWebServices.Figure4 5 - 1 illustratesthe MicrosoftWebServicesplatformarchitecture.

Figure45-1: TheMicrosoftWebServicesplatformarchitecture

AsshowninFigure45 - 1 ,theCommonLanguageRuntime(CLR)isbuiltontopofthe

systemservicesplatform(suchasWindows2000).LayeredontheCLRisthe.NET FrameworkClassLibrary,whichprovidesalargesetofservicesviaahierarchically arrangedcollectionofclassesandtypes.OntopofthisbasearetheASP.NETWeb platformandWindowsFormsenvironments.Thischapterlooksatmostofthese architecturalpieces,astheyrelatetothedevelopmentandconsumptionofWeb Services.

OneoftheprimarygoalsoftheMicrosoftWebServicesplatformistomakeiteasyto buildWebServicesthatcansolvecomplex,business-criticalproblems.Thefollowing sectionswilltakealookattheWebServicesplatformfeaturesthatmakeiteasyto createthesetypesofapplications.TheMicrosoft.NETFramework

The.NETFrameworkisMicrosoft'spremierplatformforbuildinganddeployingrobust WebServices.It providesbuilt-insupportfor creatingand consumingWebServicesin threekeyareas:

TheCommonLanguageRuntime(CLR) The.NETFrameworkClassLibrary ASP.NET

Let'sexaminesomeofthefeaturesofthesekey.NETFrameworkpieces,whichprovide arobustenvironmentforthecreationandexecutionofworld-classWebServices.

The CommonLanguageRuntimeTheCLRprovidesthefoundationforthe.NETFramework.It'sresponsibleformanaging codeatexecutiontimeandprovidesthefollowingservices:

Automaticmemorymanagement—Garbagecollectionishandledbytheruntime,relievingtheprogrammerfrommanagingmemory.This improvesthereliabilityandstabilityofapplications.

Codesafetyandsecurity—Codecanbe"lockeddown"topreventunauthorized,oruntrustedaccess.Thissecurityinfrastructureishighly flexibleandconfigurable.

Codeversioninganddeploymentsupport—Multipleversionsofcodecanberuninside-by-sidemode,thusprovidingmorereliable operationforolderapplicationsthatrelyonolderversionsofcode libraries.

Cross-languageintegration—Enablesallprogramminglanguagestosharedataconsistentlyviaacommontypesystem.

Remoting—Extendsthecallingofcomponentsacrossprocessand machineboundariesusinganextremelyefficientwireprotocol. Self-describingobjects—Metadatathatdescribesanobject's

capabilitiesisstoredwiththeobject,makingiteasytodynamically determinehowtointeractwithanobject.

Threadmanagement—Asimpleyetflexiblethreadmanagementinfrastructuremakesiteasytocreatemulti-

threadedapplications.CodethattargetstheCLRiscalledmanagedcode.Compatiblelanguagecompilersgeneratecodethatenablestheruntimetomanagetheexecutionofyourapplications.Todothis,compilersgenerateMicrosoftIntermediateLanguage(MSIL).Thisintermediatecodeisplatform-independentandcanbehostedonanyprocessorarchitecturesupportedbytheCLR.AJust-In-Time(JIT)compilerisusedtoconvertMSILintoprocessor-specificcodeatruntime.Duringexecution,CLR-managedcodeautomatically receivesthebenefitsofmemorymanagement,cross-languagedebuggingsupport, security,andmanyotherfeatures.Managedcodeispackagedintounitscalledassemblies.Thesearethebuildingblocksof.NETFrameworkapplicationsandformthefundamentalunitofdeployment,version control,reuse,andsecurity.Anassemblycontainsalloftheinformationnecessaryfor theCLRtoprovideitsservices.

AmajordesigngoaloftheCLR(asistrueofallthepiecesintheWebServicesarchi- tecture)istomakethedevelopmentprocesseasier.Asyoucansee,theCLRprovidesanexcellentexecutionenvironmentforWebServices.Thedeveloperdoesn'tneedtoprovideandmanagethesefeatureshimself,makingitquickandeasytobuildanddeployrobustWebServiceapplicationsthattakeadvantageoftheCLR.

The.NETFrameworkClassLibraryThe.NETFrameworkClassLibraryisacollectionofclassesthatareorganizedintoa singlehierarchicaltreeofnamespaces.Theclasslibraryprovidesaccesstosystem featuresviaclasses,interfaces,andvaluetypesthatgreatlyenhanceprogrammer productivityandsimplifythedevelopmentprocess.Theclasslibraryisbuiltontopofthe CommonLanguageRuntime,whichwasjustdiscussed.Therefore,it'salsomanaged

codethatreceivesallthebenefitsprovidedbytheCLR.

AttherootoftheclasslibraryhierarchyistheSystemnamespace.Thisnamespace containsover100coretypesandclassesthatareusedbyall.NETapplications.In additiontotheSystemnamespace,theclasslibrarycontainsnamespacesforabstract baseclassesandderivedclassimplementations.ThisincludesfileI/O,messaging, networking,security,andaccesstotheInternet.Youcanusetheseclassesas-isor derivefromthemtocreateyourownimplementations.The.NETFrameworkusesadot-basednamingschemetorepresentgroupedclassesandtypesthatmakeupanamespace.Namespacesmakeiteasiertosearchforand referenceclassesandtypes.Thenamespacenameincludeseverythingfromthe beginningofthenameuptothelastdotinthename.Theremainingpartofthename identifiesthetypename.Forexample,theSystem.WebnamespacedefinestheWeb type,whichbelongstotheSystemnamespace.Table45 - 1 listssomeofthe namespacesthatimplementfeaturesofWebServicesonthe.NETplatform.

Table45-1:.NETWebServiceNamespaces

Namespace Purpose

System.Web.Services Contains classes that enable youto buildand consume Web Services.

Table45-1:.NETWebServiceNamespaces

Namespace Purpose

System.Web.Services.Description Contains classes that enable youto describe aWeb Service viathe Web Service Descripti on Languag e (WSDL).

System.Web.Services.Discovery Contains classes that impleme ntthe discoveryprocessusedby Web Service consumersto locate available Web Services.

System.Web.Services.Protocols Contains classes that implementthe protocols usedto exchangeWeb Service message s between Web Services andWeb Service consumers.

ASP.NETASP.NETisaunifiedWebdevelopmentplatformthatprovidesadvancedservicesfor buildingWebapplicationsandWebServices.Itprovidesanewprogrammingmodeland infrastructurethatallowsyoutocreatepowerfulWebapplicationswithunprecedented speed,flexibility,andease.ASP.NETisfullysupportedbythe.NETFramework,allowing youtotakefulladvantageoftheCommonLanguageRuntime(CLR),typesafety, inheritance,andalloftheotherfeaturesofthatplatform.

ASP.NETofferstwoprogrammingmodels:WebFormsandWebServices.Developers canuseWebFormstocreatethemoretraditionaltypeofWebapplicationwhereusers interactwithindividualpagesandinputforms.WebServices,ofcourse,isthefocusof thispartofthebook.

BothoftheseprogrammingmodelsoffertwotechniquesforcodingWebpagesandWeb Services.Usingembeddedimplementationcode,thelogicforaWebpageorWeb Serviceisembeddedinthepageitself(muchlikethatofthetraditionalASP programmingenvironment).Contrastthistechniquewiththecode-behindfileapproach. Usingcode-behind,thelogicforaWebpageorWebServiceisstoredinaseparatefile fromtheuserinterfaceofaWebpageortheentrypointdeclarationofaWebService.

Bydefault,VisualStudiocreatesASP.NETWebFormsandWebServicesbyusingthe code-behindtechnique.Thiscreatesacleardistinctionbetweenthedefinitionoftheuser interface(orWebService)andthecodethatimplementsitsbehavior.

ThenextfewsectionssurveysomeofthefeaturesoftheASP.NETplatformthatare availabletoASP.NETWebServices.

ASP.NETapplicationsAnASP.NETapplicationconsistsofallthefiles,pages,handlers,modules,and executablecodeinaWebservervirtualdirectory(andanysubdirectories).WebServices

arealsoASP.NETapplicationsandthereforearegovernedbythesameconfiguration rulesasanyotherASP.NETapplication.EachASP.NETapplicationcanincludeanoptionalGlobal.asaxfileintherootvirtualdirectory.Thisfilecontainshandlersforapplication-leveleventsthatcanberaisedby ASP.NET.Forexample,youcanhandlesucheventsasApplication_OnStartand Application_OnEndintheGlobal.asaxfile.Inadditiontotheseevents,youhaveaccesstoanyeventsexposedbyHTTPModules.AnHTTPModuleisaclassthatcanprocessinformationfromanyHTTPrequestsmade toyourASP.NETapplication.Youcancustomizeorextendmodulessuppliedby ASP.NETorcreateyourown.AnyeventsraisedbyHTTPModulesarehandledwithin theGlobal.asaxfile.WebServiceprojectscreatedwithVisualStudioautomaticallycreateaGlobal.asaxfile.Thisemploysacode-behindfiletocontainthecodethathandlestheaforementioned events.Thecode-behindfileisdeclaredintheGlobal.asaxfilebyusingtheASP.NET Applicationdirective:

Web Services InfrastructureWebServiceDirectoriesWebServiceDiscoveryWebServiceDescriptionWebServiceWireFormats

WebServicediscoveryWebServicediscoveryistheprocessoflocatingoneormorerelateddocumentsthat describeaspecificWebService.ThesecapabilitiesaredescribedinastandardwaybyusingtheWebService DescriptionLanguage(WSDL),whichisanXMLgrammarspecificallydesignedforthis purpose.

BeforeyoucansubmitrequeststoaWebService,youmustknowhowtoformata requestforaparticularservice.Itmustbeintheformofamessagethatencodesthe operationrequested(suchasconvertingatemperaturefromoneunittoanother),aswell asanydatarequiredtocarryouttheoperation(suchastheinputtemperature,thesourceunits,andthetargetunits).Inaddition,youmustknowwhetherornottoexpectaresponsemessagefromtheWebServiceandwhatformatthisresponsewilltake(such astheconvertedtemperaturevalue).

TheWebServicediscoveryprocesspermitsaconsumertosearchforandlocatethe WSDLdocumentforaWebService.AconsumermusthavetheWSDLdocumentbefore anyrequestscanbeproperlyformattedanddeliveredtotheWebService.

TheDISCOspecificationdefinesanXML-basedgrammarandalgorithmfordiscovering theexistenceofWebServicesandlocatingtheirWSDLdocuments.UsingDISCO,you candefinesearchtreesthatareprocessedaccordingtotheDISCOalgorithmtolocate WebServicedescriptions.

DiscoverydocumentsareXMLfilesthathaveafiletypeof.discoor.vsdisco (whenautomaticallygeneratedbyVisualStudio).Adiscoverydocument isacontainerfortwotypesofelements:pointerstoWSDLdocuments,andpointersto otherdiscoverydocuments.ThesepointerstaketheformofURLsandcanbeabsolute orrelative.The<contractRef>elementisusedtolinktoWebServiceWSDL documents,whereasthe<discoveryRef>elementisusedtolinktootherdiscovery documents.

WebServicedescriptionAWebServicedescriptionisanXMLdocumentthatdefinesthecapabilitiesofaWeb Service.UsingtheWebServiceDescriptionLanguage(WSDL)XMLgrammar,youcan clearlyandunambiguouslydefinetheWeb-addressableentrypoints,therequest messagesthataWebServicewillaccept,andtheresponsemessagesaWebService canreturn.Alsoincludedinthisdescriptionarethesupportedprotocolbindingsanda descriptionofthedatatypesprocessedbytheWebService.

Recallthatthe.NETFrameworksupportsself-describingassemblies.Thisis accomplishedbystoringmetadatawiththeassemblythatdescribestheinterfaces,data types,andotherinformationabouttheclassesintheassembly.Usingtheself-describing natureof.NETassemblies,the.NETFrameworkcangenerateWSDLdocumentsto describeWebServicecapabilitiesfromthe.NETassembliesthatcontainASP.NETWeb Servicecode.

Chapter46:SOAPWhat Is SOAP?TheSimpleObjectAccessProtocol(SOAP)isalightweight-XML-basedprotocolfor exchanginginformationinadecentralized-distributedenvironmentsuchasthatoffered bytheInternet.Inotherwords-SOAPenablestwoprocesses(possiblyondifferent machines)tocommunicatewitheachotherregardlessofthehardwareandsoftware platformsonwhichthey'rerunning.OneofthegreatestbenefitsofSOAPisthatit'spartofanopenprocessthathasbeen embracedatanunprecedentedlevelbymostofthemajorhardwareandsoftware vendors.TheSOAPspecificationisanopentechnology(havingbeensubmittedtothe W3C)thatprovidesthebasisforapplication-to-applicationintegrationknownasWeb Services.

BenefitsofusingXMLwithSOAP

ThefundamentalbuildingblockofSOAPisXML.SOAPdefinesaspecializedyetflexible XMLgrammarthatstandardizestheformatandstructureofmessages.Messagesare-in turn-thefundamentalmethodforexchanginginformationbetweenWebServicesand WebServiceconsumers.UsingXMLtoencodeSOAPmessagesprovidesseveral benefits-suchasthefollowing:

It'shuman-readable-makingiteasiertounderstandanddebug. Parsersandrelatedtechnologiesarewidelyavailable. It'sanopenstandard. ManyrelatedtechnologiesthatcanbeleveragedinSOAPare included.

Thus-XMLisanaturalchoiceforencodingSOAPmessages-anditcontributestothe simplicityofthespecification(atleastinrelationtomorecomplexbinaryprotocolssuch asCOMandCORBA).

The SOAP SpecificationTheSOAPprotocolspecificationisaW3C-submittednotethat'snowundertheumbrella oftheXMLProtocolsworkinggroup.Version1.2ofthespecification(thefollow-upto version1.1)wasunderdevelopmentasaworkingdraftatthebeginningofJuly2001. The.NETFrameworkandASP.NETWebServicesproduceandconsumeSOAP messagesthatarecompliantwithversion1.1oftheSOAPprotocolspecification.

TheSOAPprotocolspecificationhasfourprimaryparts,eachofwhichhasaspecific purpose:Adefinitionforamandatory,extensiblemessageenvelopethatencapsulates

allSOAPdata.TheSOAPenvelopeisthefundamentalmessagecarrier thatformsthebasisforSOAPmessageexchangebetweenSOAP-aware endpoints.ThisistheonlypartoftheSOAPspecificationthat'smandatory.

Asetofdataencodingrulesforrepresentingapplication-defineddatatypes,andamodelforserializingdatathatappearswithintheSOAPenvelope.

AdefinitionforanRPC-style(request/response)messageexchangepattern.SOAPdoesn'trequiretwo-waymessageexchanges,butWebServices typicallyimplementsuchRPC-stylerequest/responsepatternswhenused withHTTPasthetransportprotocol.Thus,therequest/responseRPC-style protocolisafunctionofHTTPandnotofSOAP.

AdefinitionforaprotocolbindingbetweenSOAPandHTTP.ThisdescribeshowSOAPmessagesaretransmittedusingHTTPasthetransport protocol.

SincetheSOAPenvelopeistheonlymandatorypartofthespecification,let'sfirsttakea

lookattheelementsthatmakeupaSOAPmessage.

Elements ofa SOAP MessageASOAPmessageiscomposedofthethreefollowingprimaryelements,eachofwhich performsaspecialpurpose:

Envelope—ServesasacontainerfortheremainingSOAPmessageelements.

Header—Containsoptionaldatathataconsumermayormaynotberequired tounderstandinordertoprocessthemessageproperly.Thisistheprimary extensibilitymechanismofSOAP.

Body—Containstheactualencodingofamethodcall,andanyinput argumentsoranencodedresponsethatcontainstheresultsofthemethod call.

Thenextfewsectionslookatthesemessageelementsindetail.

TheSOAPenvelopeTheSOAPenvelopeelementisarequiredpartofaSOAPmessage.Itservesasa containerforallremainingSOAPmessageelements.Typically,thisincludestheSOAP headerandbodyelements.Inaddition,theenvelopedefinesthenamespacesusedby theseelements.Figure46 - 1depictsthestructureofacompleteSOAPmessage.

Figure46-1: TheSOAPmessagestructureTodeliveraSOAPmessagetoanendpoint,addressinginformationthat'sspecifictothe transportprotocolbindingisusedtoensurethatthemessageisdeliveredtothecorrect endpoint.It'smuchlikeputtingarecipient'snameandaddressonarealenvelopesoa postalauthoritycandeliverit.InthecaseofHTTP,acustomHTTPheadernamed SOAPActionisusedtodirectthemessagetotheproperendpoint.

TheSOAPheader

TheSOAPheaderelementisanoptionalpartofaSOAPmessage.Itdefinesadditional informationthatcanberelatedtothemethodrequestinthebodyelement.Or,more likely,itdefinesinformationindependentofthemethodrequestthat'srequiredor otherwiseusefultoyourapplication.SOAPdoesn'tdefinethespecificcontentsor semanticsforaSOAPheader.SOAPheadersarequitesimilarinconcepttotheMETAtagsfoundinHTMLdocuments. Theydefinemetadatathatcanbeusedtoprovidecontextto,orotherwisedirectthe processingof,themessage.

TheSOAPbody

TheSOAPbodyelementisarequiredpartofaSOAPmessagethatcontainsthedata specifictoaparticularmethodcall,suchasthemethodnameandanyinput/output argumentsorthereturnvaluesproducedbythemethod.ThecontentsoftheSOAPbody dependonwhetherthemessageisarequestoraresponse.Arequestmessagecontainsmethodcallinformation,whereasaresponsemessagecontainsmethodcallresultdata.

SOAP Data Type SupportTheSOAPspecificationdefinesdatatypesupportintermsofXSD,theXML Schemaspecification.Thisspecificationdefinesstandardsfordescribing primitivedatatypes,aswellascomplex,hierarchicalstructures.Asyouwould expect,there'ssupportforintegers,strings,floats,andmanyotherprimitive types,aswellaslists(orarrays)oftheseprimitivetypes.

Inadditiontoprimitivetypes,user-definedstructurescanberepresented.This pavesthewayfordescribingcomplex,hierarchicaldatarelationshipssuchas thosefoundinaninvoiceorpurchaseorder.Thebottomlinehereisthatit's possibletodescribeanytypeofdatausingXSD.Thus,SOAPcansupportany datatype,fromthebuilt-inprimitivesdefinedbyXSDallthewaytoany arbitraryuser-definedstructure.ThisisoneoftheprimaryreasonsthatSOAP isthepreferredprotocolforexchangingWebServicerequestandresponse messages.ItenablesWebServicestoacceptaswellasreturnanytypeofdatathatcanberepresentedbyanXSDschema.TheCommonLanguageRuntime(CLR)within.NETsupportsawidevarietyof thecommondatatypes.Allofthesedatatypesaresharedequallyacrossallof

the.NETlanguagesandalsohaveawell-definedmappingtoXSDdatatypes, asshownin Table46 - 1 .

Table46-1:XSDDataTypesvs.CLRDataTypes

XMLSchemaDefinition CommonLanguageRuntime

Boolean BooleanByte N/A

Table46-1:XSDDataTypesvs.CLRDataTypes

XMLSchemaDefinition CommonLanguageRuntime

double Doubledatatype N/Adecimal Decimalenumeration Enumfloat Singleint Int32long Int64Qname XmlQualifiedNameshort Int16string StringtimeInstant DateTimeunsignedByte N/AunsignedInt UInt32unsignedLong UInt64unsignedShort UInt16

SOAP in the .NET FrameworkFortunately,everythingthatyou'velearnedaboutSOAPuptothispointislargely unnecessarywithrespecttoimplementingsimpleASP.NETWebServices.Thisis becauseASP.NETandthe.NETFrameworkautomaticallygenerateandprocessSOAPmessagesforyourWebService,leavingyoutofocusonwritingthelogicofyourWebServiceapplicationusingafamiliarobject-orienteddesignapproach.

However,moresophisticatedWebServicesmayrequireaccesstotheSOAPmessages inordertoaddcustomheaders,examineincoming/outgoingSOAPmessages,or otherwisealterthedefaultformatofmessagesgeneratedbythe.NETXMLserializer wheninteroperatingwithSOAPmessageprocessorsonotherplatforms.

IfSOAPmessagecustomizationbecomesnecessaryforaparticularWebServicethat youwanttoimplement,the.NETFrameworkandASP.NETcangiveyouaccesstothe SOAPmessages.ThissectionwilllookatthefollowingfeaturesprovidedbyASP.NET forcustomizingthedefaultSOAPmessageformatsandcontents:

SOAPheadersSOAPextensionsSOAPexceptions

The .NETSoapHeaderattributeAsyousawinthelastexample,theSoapHeaderattributeisusedtoenablesupportfor SOAPheadersonspecificWebServicemethodsthataredeclaredwiththeWebMethod attribute.Specifically,theSoapHeaderattributeissuppliedwiththenameofamember variablethat'saninstanceofyourcustomSoapHeaderclass.Technically,thissyntaxis settingapropertyoftheSoapHeaderattribute,namelytheMemberName-property.The

SoapHeaderattributesupportsthesethreeproperties: MemberName Direction Required

TheMemberName-propertyoftheSoapHeaderattributeidentifiesthenameoftheclass variablethatdeterminesthetypeoftheSOAPheader.Inthisexample,thetypeofthe SOAPheaderisobtainedfromtheAuthSoapHeadermembervariablewithinthe MyWebServiceclass.TheDirectionpropertyoftheSoapHeaderattributeisusedtospecifyinwhichdirectiontheheaderisexpectedtobesupplied.Bydefault,SOAPheadersareattached tomethodrequestsonlyandaresaidtobeinboundtotheWebService.Usingthis property,youcanchangethisdefaultbehavior.TheDirectionpropertyacceptsan enumerationnamedSoapHeaderDirectionthatsupportsthefollowingthreevalues:

SoapHeaderDirection.In:DeclaresthattheSOAPheaderisexpectedtobesuppliedtorequestmessagesgeneratedbytheWebService consumer.

SoapHeaderDirection.Out: DeclaresthattheSOAPheaderis expectedtobesuppliedbyresponsemessagesgeneratedbytheWeb Service.

SoapHeaderDirection.InOut: DeclaresthattheSOAPheaderisexpectedtobesuppliedbyboththerequestandresponsemessages.

Here'sanexampleoftheDirectionpropertyinVB.NET:

<SoapHeader("AuthSoapHeader", Direction:=SoapHeaderDirection.Out>Finally,theRequiredpropertyoftheSoapHeaderattributeisaBooleanpropertythat controlswhetherornottheSOAPheaderisrequired.Bydefault,thispropertyissetto true.Thismeansthatiftheheaderisn'tsupplied,aSoapexceptionwillberaised.Setting thispropertytofalsemakestheheaderoptional,asinthefollowingexample:

<SoapHeader("AuthSoapHeader", Required:="false")>

ThesearethebasicsforusingSOAPheadersinASP.NETWebServices.Buthowdoes aconsumeraccesstheSOAPheadertosetthevaluesthatneededtobepassed? Fortunately,thesedetailsarehandledforyoubyASP.NETwhentheWebServiceproxy classiscreated.ThismakessettingSOAPheadervaluesassimpleassettingaproperty ontheproxyclassinstance.You'lllearnallaboutWebServiceproxyclasses(theprimarymeansbywhichaconsumerinteractswithaWebService)inthechapteraboutconsumingWebServices.

Now,let'slookataslightlymoreadvancedfeatureofASP.NETcalledSOAPextensions.

UsingSOAPextensions

OneofthemoreadvancedfeaturesofSOAPwithinthe.NETFrameworkistheSOAP extensionstechnology.ThisletsyouinspectormodifyaSOAPmessageatspecific stagesinmessageprocessingoneithertheclient(theconsumeroftheWebService)or server(theWebServiceitself).Ofcourse,thisassumesthattheclientandserverare bothbasedonthe.NETFramework.

Thisisapowerfulfeaturebecauseitallowsyoutoimplementsomeveryinteresting applicationsthatcanbeleveragedbyWebServicesand/ortheirclientsinacompletely transparentmanner.Forexample,youcancreateextensionsthat

Encryptmessagestoprotectthecontentswhileintransit. Compressmessagestoreducethesizeofthetransmissionstream. Logmessagesforauditingortracingmessageactivity(especiallyuseful indebugging). ProcessSOAPattachments.

Chapter47:BuildingaWebServiceThischapterteachesyouhowtobuildasimpleWebServiceusingVisualBasic.NETin MicrosoftVisualStudio.Itgoesstep-by-stepthroughtheprocessofcreatingaWeb ServicethatconvertsgiventemperaturesbetweenFahrenheit,Celsius,Kelvin,and Rankine.Alongtheway,I'lldescribesomeoftheVisualStudioimplementationoptions relatedtobuildingWebServices.

Creating the Temperature Conversion Web ServiceThetemperatureconversionWebServiceconvertsspecifiedtemperaturevaluesfrom FahrenheitorCelsiustoeitherFahrenheit,Celsius,Kelvin,orRankine.Eachofthese unitconversionsisdefinedbyawell-

knownarithmeticformulathatcanbeeasily representedinVisualBasicanddoesn'trequirealotofcode.Thischapterkeepsit simplesothatyoucanfocusmoreonthevariousarchitecturalelementsofASP.NET WebServices,ratherthanthedetailsofthealgorithmimplementedbythecode.

Beforeyoustartbuildingthisservice,youshouldknowalittleaboutthefollowing componentsofthisexample:Temperatureconversionformulas

Table47-1:TemperatureConversionFormulas

From/To Fahrenheit(F)

Celsius(C)

Kelvin(K)

Rankine(R)

Celsius ((C*9)/5)+32

N/A C+273.15

F+459.67

Fahrenheit N/A ((F-32)*5)/9

C+273.15

F+459.67

MethoddescriptionsMethodargumentsMethodbehavior

TemperatureconversionformulasTable4 7 - 1 showstheconversionsthataresupportedbytheserviceandthe correspondingformulasusedtoperformtheconversion:

Asyoucanseefromthetable,someoftheconversionsarespecifiedassuminganinitial conversiontoanotherunit.Forexample,toconvertaCelsiustemperaturetoRankine, thetemperaturevalueisfirstconvertedtoFahrenheitandthentheremainingconversion rulesareapplied.

Finally,inkeepingwiththegoalofcodesimplicityandbrevity,theserviceonlysupports temperatureconversionsfromCelsiusorFahrenheittoanyoftheotherapplicableunits.

MethoddescriptionThetemperatureconversionWebServicesupportsasinglemethodnamedCTemp, whichismodeledalongthelinesoftheclassicVisualBasictypeconversionfunctions suchasCBool,CLng,CDbl,etc.Theobviousdifference,ofcourse,isthatyou're convertingtoothernumericunitsinsteadofconvertingtootherdatatypes.

MethodargumentsThetemperatureconversionmethodacceptsthethreeargumentsthataresummarized inTable 47 - 2 .Table47-2:TemperatureConversionMethodArguments

ArgumentName DataType

Comments

Temperature Decimal Any numeric valuethat canbe specifiedby the Decimal datatype.

FromUnits String Valid valuesare Cfor Celsiusor FforFahrenheit.

ToUnits String Valid valuesare Cfor Celsius,F forFahrenheit,KforKelvin,and Rfor Rankine.

ThemethodreturnsaDecimalresult,whichisthevalueoftheconversiontotheunitsspecifiedintheToUnitsargument.

MethodbehaviorIftheFromUnitsandToUnitsargumentsarethesame,themethodcallissuccessful andtheTemperatureargumentisreturnedunchanged.IftheFromUnitsand/or ToUnitsdon'tspecifyvalidunitidentifiers,anArgumentExceptionexceptionis thrown.Likewise,iftheconversionspecifiedbytheFromUnitsandToUnits argumentsisn'tsupported,anArgumentExceptionexceptionisthrown.

BuildingtheWebServiceinVisualStudioTheVisualStudioIntegratedDevelopmentEnvironment(IDE)isahighlyproductivetool forbuildingWebServices.AsyoulearnedinthepreviouschaptersofPartVI I ,Web Servicesrequireanaddressableentrypointfile,anassemblythatimplementsthe functionalityoftheservice,aWebServiceDescription(WSDL)document,anoptional Discovery(DISCO)document,andanoptionalUDDIregistration.Fortunately,the.NET FrameworkandVisualStudioimplementmuchofthisinfrastructureforyou,allowingyou tofocusyoureffortsonthefeaturesoftheWebService.

WebServicesbuiltwithVisualStudioareASP.NETWebServices.Thismeansthata WebServicebuiltinVisualStudioleveragestheASP.NETinfrastructure,tools,and runtime.Ofcourse,ASP.NETitselfisbuiltuponthefoundationofthe.NETFramework

andtheCommonLanguageRuntime(CLR),providingallofthebenefitsofthese technologiestoyourWebServiceimplementation.

TheserelationshipsarealsoimportantbecausetheyaffectthephysicalstructureofWeb ServiceswithintheVisualStudioenvironment.Thepowerofthismodelisquiteevident asyoubegintodissectthevariouspiecesofaWebServiceonthe.NETplatformand understandtheirfeatures.Thischaptercoversthesepointsasyouworkyourway throughthetemperatureconversionWebServiceimplementation.

BeforeyoustartworkingwithVisualStudiotobuildaWebServiceapplication,youmust considerafewenvironmentalfactorsrelatedtoyoursoftwareandnetworkconfiguration. Theseconsiderationsdirectlyaffecthowyoubuild,debug,anddeployWebServices usingVisualStudio.Theyfallintotwocategories:

WebServiceDevelopmentEnvironment—DescribesthesoftwareenvironmentnecessaryfordevelopingaWebService. WebServiceProjectAccessMethods—Describesthemethodsfor

managingtheWebServiceprojectfilesonaWebserver.

ASP.NETWebServicedevelopmentenvironment requirementsThetypicaldevelopmentenvironmentforanASP.NETWebServiceapplicationusually consistsofthefollowingelements:

ApersonalworkstationcontainingtheVisualStudiodevelopmentsoftwareand.NETframeworkSDKusedtodesignandbuildyourWebService.

AdevelopmentWebserverthat'sconfiguredtohostandruna development(non-release)versionofyourWebService.

AproductionWebserverthat'sconfiguredtohostthefinalruntime(release)versionofyourWebService.

CreatingaWebService projectThefirststeptobuildingthetemperatureconversionWebServiceoutlinedatthe beginningofthischapteristocreateaWebServiceprojectinVisualStudio.Afteryou've startedVisualStudio,chooseNewfromtheFilemenuandthenchooseProjectfromthe submenu.VisualStudiodisplaystheNewProjectdialogshowninFigure 4 7 - 3 .

Figure47-3: VisualStudio.NETNewProjectdialogbox

TheNewProjectdialogboxiswhereyoucancreatemanydifferenttypesofprojects basedonpreconfiguredprojecttemplates.Thesetemplatesdefinesuchthingsasthe basicstructureofaproject,thefilestobeincluded,andtheparametersnecessaryto buildanddeployyourproject.

TocreateaVisualBasic.NETWebServiceproject,followthesesteps:1.ChoosetheVisualBasicProjectsfolderfromthelistofprojecttypes

ontheleft.Next,choosetheASP.NETWebServiceiconfromthe listoftemplatesontheright.2.Specifyanameforyourproject.ThesampleprojectisnamedCTemp,

soenterCTempintheNametextbox.Noticethatasyoutypeinto thetextbox,VisualStudioautomaticallyfillsouttheprojectlocation, showingyouwhereyourprojectfileswillbestored.

3.TheprojectlocationtextboxdefineswhichWebserveryouusetostoreandexecuteyourWebServiceprojectfilesduring developmentinVisualStudio.

B

ydefault,theprojectlocationpointstothelocalWebserveronyourcomputer.MycomputernameisJDC7200CTE,whichresultsinarootlocation ofhttp://jdc7200CTE.Yournamewillbedifferent,ofcourse.Usually,you shoulddevelopandtestyourWebServiceusingyourlocalcomputer'sWeb serverbecausethat'sthesimplestconfiguration.

UnderneaththeLocationtextbox,thedialogboxdisplaysthecompletepath toyournewWebService.ThisisthepaththatconsumersofyourWeb Servicecanusewhencallingyourservice(atleastwhileit'sunder development).

4.ClicktheOKbuttontocreatetheproject.Atthispoint,VisualStudioconnectstotheWebserveryouspecifiedintheLocationtextbox andcreatestheWebServiceprojectfilestructure.VisualStudio alsocreatesasolutionfileonyourlocalcomputer.

Note IftheWebserveryouspecifiedisn'tonyourlocalcomputer,thesolutionfileistheonlyfilethat'sstoredlocally.

WhenVisualStudiohasfinishedcreatingtheproject,theIDElookssimilartoFigure47 - 4 .

Figure47-4: VisualBasic.NETWebServiceprojectinVisualStudio

CreatingWeb methodsNowthatyou'veupdatedtheclassname,you'rereadytoinserttheimplementationcode foryourWebService.Beginbyenteringthefollowingmethoddeclarationintothecode windowinsideyourTempConverterclass:

<WebMethod()>PublicFunctionCTemp(_

ByValTemperatureAsDecimal,_ ByValFromUnitsAsString,_

ByValToUnitsAsString)AsDecimal

Adding theimplementationcode

SelectCaseFromUnits.ToUpper.Chars(0) Case"F"'Fahrenheit

SelectCaseToUnits.ToUpper.Chars(0)

Case"F"'Noconversionnecessary

ReturnTemperature

Case"C"'ConvertFahrenheittoCelsius

Return((Temperature-32)*5)/9

Case"K"'ConvertFahrenheittoKelvin

Return(((Temperature-32)*5)/9)+273.15

Case"R"'ConvertFahrenheittoRankine

ReturnTemperature+459.67

CaseElse

'Throwexception

ThrowNewArgumentException("BadToUnitsarg.") EndSelect

Case"C"'Celsius

SelectCaseToUnits.ToUpper.Chars(0)

Case"C"'Noconversionnecessary

ReturnTemperature

Case"F"'ConvertCelsiustoFahrenheit

Return((Temperature*9)/5)+32

Case"K"'ConvertCelsiustoKelvin

ReturnTemperature+273.15

Case"R"'ConvertCelsiustoRankine

Return(((Temperature*9)/5)+32)+459.67

CaseElse

'Throwexception

ThrowNewArgumentException("Bad ToUnitsarg.") EndSelect

CaseElse

'Throwexception

ThrowNewArgumentException("BadFromUnitsarg.") EndSelect

EndFunction

Building the Web ServiceNowthatyou'veaddedalloftheimplementationcodeforyourCTempWeb Service,you'rereadytobuildit.WhenyoubuildaVisualStudioASP.NETWeb Serviceproject,thefollowingoccurs:

1. VisualStudiosavesallofthefilesintheprojectyoumodifiedsincethelastbuild.

2. VisualStudiocopiesthe{servicename}.asmxfileandthe defaultprojectfilestothedevelopmentWebserver.

3. The{servicename}.asmx.vbclassfileandtheGlobal.asaxclassfilearecompiledintotheproject.dllfile,whichisthencopiedtotheserverinthedefault\Bindirectoryofthetargetvirtual directory.Iftheprojectissettocompileadebugversion,Visual Studiocreatesaproject.pdbfileinthe\Bindirectory.

TobuildtheCTempWebService,chooseBuildfromtheBuildmenu.VisualStudiodisplaystheOutputwindowtoshowtheprogressandfinalresultsofthe buildprocessforyourproject,asshowninFigure47 - 6 .

Figure47-6: ResultsofbuildingtheWebServiceinVisualStudioNowthatyou'vesuccessfullybuiltyourWebService,you'rereadytotestit. Thenextsectio n coversWebServicetesting.

Testing the Web ServiceVisualStudioandthe.NETFrameworkprovideseveralmethodsyoucanusetotestyourWebService.ThesimplestandquickestmethodtotestyourWebServiceistousea WebbrowserusingtheHTTP-GETprotocol.Thistechniquedoesn'trequiredevelopinga consumerapplication.

Note ThistechniqueworksonlyfortheHTTP-GETprotocolsupportthat'sprovidedbythebrowser.Bydefault,anASP.NETWeb ServicebuiltinVisualStudiosupportstheHTTP-GET,HTTP- POST,andHTTP-SOAPprotocols.

InadditiontousingaWebbrowserwithHTTP-GET,youcanalsotestyourWebService usingaWebbrowserwithHTTP-POST,withaslightmodificationtothedefaultASP.NETpageusedtoviewWebServices.Finally,youcantestyourWebServiceby developingacustomconsumerapplication.TestingtheWebServicewithHTTP-GET

UsingaWebbrowsertotestyourWebServicewiththeHTTP-GETprotocoldoesn't requireyoutodevelopaconsumerapplication.Therefore,thisisaquickandeasyway toperformsomeinitialtestingofyourWebService.TheHTTP-GETprotocolencodes data(inthiscase,methodarguments)asquerystringparameterswhenpostingtothe server.Thisencodingmethodisusedtopassthepropermethodinputargumentsas querystringarguments.

TherearetwowaystoinvoketheHTTP-GETprotocolusingaWebbrowsertotestyour WebService.Youcanusethebuilt-intestpageofferedbytheASP.NETruntimeoryou canencodethecompleteURLtoyourWebServiceusinglocation,methodnameandanyinputargumentsasquerystringparametersintheaddressbarofyourbrowser.ThissectionillustrateseachofthesetechniquesusingtheCTempWebServiceasan example.

Chapter48:DeployingandPublishingWebServicesDeployingaWebServiceenablesittoexecuteonaspecifichostWebserver,whereas publishingaWebServiceenablespotentialconsumerstolocateandinterrogatethe capabilitiesoftheWebServicebeforeactuallycallinganymethodsoftheservice.This chapterdiscusseswhatyouneedtodobeforedeployingaWebService,theoptionsfor deployingandpublishingaWebServiceusing.NETtechniques,andthesupportbuilt intoVisualStudio.

Deployment PreparationBeforeyoudeployaWebService,youmustmakesurethattheWebService specifiesauniqueXMLnamespace.Thisname- spaceisusedwithintheWeb ServiceWSDLdocumenttouniquelyidentifythecallableentrypointsofthe service.Asmentionedin Chapter4

Table48-1:FilesDeployedwithaWebService

Folder File Description\inetpub\wwwroot\CTemp CTemp.asmx TheWeb Service entrypoint file.The

folder containing thisfile shouldbe configured asaWeb application directoryin IIS.

Global.asax The ASP.NET application startupfile.

Web.config The ASP.NET application configurationfile.

\inetpub\wwwroot\CTemp\bin

CTemp.dll TheWeb Service assembly thatcontainstheimplementationclasses fortheWeb Service,as wellasany dependent assemblies thataren't partofthe.NETFramework.

7,thedefaultWebServicenamespaceissettohttp://tempuri.org/whenyou'rebuildingaWebServiceinVisual Studio.NowthatyouarereadytodeployandpublishyourWebService,you mustchangethistemporarynamespacedesignatortoapermanentvalue.

BeforeyoudeploytheCTempWebService,youneedtochangethedefaultname-spacetoamoresuitablevalue.Todothis,followthesesteps:

1. StartVisualStudio.2. LoadtheCTempproject.3. IftheimplementationcodeintheCTemp.asmx.vbfileisnot displayed,openitbyright-

clickingonthefileintheSolutionExplorer windowandchoosingOpen.4. OntheTempConverterclassdeclarationline,addthe

<WebService>attributealongwiththeNamespacepropertyand setittotheappropriatevalue.

Deploying Web ServicesGenerallyspeaking,thedeploymentprocessforaWebServiceinvolvescopyingthe WebServiceentrypointfile(the.asmxfile),theWebServiceassemblyalongwithany dependentassemblies(excludingthe.NETframeworkassemblies),andrelatedsupport files(suchastheWebServicecontractfile)toanappropriatelyconfiguredvirtual directoryfilestructureonthetargetWebserver.

Insharpcontrastfromdeployingprevious-generationWindowsapplications,Web Servicestypicallyareeasytodeploy.VisualStudiomakesthisprocesseveneasierby providingseveraldeploymentoptionsthatareavailabledirectlywithintheVisualStudio environment.AtypicalWebServicebuiltinVisualStudioconsistsoftheWebServiceentrypointfile(the.asmxfile),theWeb.configfile,theWSDLfile,theDISCOfile,theWebService assemblythatcontainstheimplementationclassesfortheWebService,andany dependentassembliestheWebServicereferences(excludingthe.NETFramework).Table4 8 - 1 summarizesthestandardfilestructurefordeployingtheCTempWebService builtwithVisualStudio.

WebServicedeploymenttools

ThereareseveralchoicesfortoolsyoucanusetodeployaWebService,dependingon thecomplexityandcircumstancesofthatparticularproject.Thesechoicesare

VisualStudioWebSetupProject VisualStudioProjectCopy DOSXCOPYCommand GenericFileTransferMethod

Publishing Web ServicesPublishingaWebServiceenablespotentialconsumerstolocateandinterrogateservice descriptionsthatinstructtheconsumeronhowtointeractwiththeWebService.The processoflocatingandinterrogatingWebServicedescriptionsisreferredtoasthe discoveryprocess.ThetwomethodsforenablingdiscoveryofaWebServiceareDISCO andUDDI.Youmaychoosetouseoneorbothofthesemethodsbasedontheconsumeraudienceyouaretryingtoreach.

Table48-1:FilesDeployedwithaWebService

Folder File Description\inetpub\wwwroot\CTemp CTemp.asmx TheWeb Service entrypoint file.The

folder containing thisfile shouldbe configured asaWeb application directoryin IIS.

Global.asax The ASP.NET application startupfile.

Web.config The ASP.NET application configurationfile.

\inetpub\wwwroot\CTemp\bin

CTemp.dll TheWeb Service assembly thatcontainstheimplementationclasses fortheWeb Service,as wellasany dependent assemblies thataren't partofthe.NETFramework.

PublishingwithDISCOConsumersofWebServicesenactadiscoveryprocesstolocatethoseservices.The discoveryprocesssearchesforXML-encodeddiscoverydocumentsthatcontainpointers tootherresourcesthatdescribetheWebService.EncodingdiscoverydocumentsinXMLenablestoolssuchasVisualStudiotoprogrammaticallydiscovertheavailabilityof WebServices(ifyouknowtheURLtotheserver).ThisishowtheWebReference metaphorworksinVisualStudiowhenyouprovideitwithaspecificdiscoveryURL. Alternatively,youcanusethedisco.exetoolthatcomeswiththe.NETFramework SDKtodiscoverWebServices.WebServicediscoveryviaVisualStudio'sWebReferencefeatureortheNET FrameworkSDK'sdisco.exetoolisusefulwhentheconsumerknowstheURLtothe serverthat'shostingtheWebServiceortheapplicationvirtualdirectory.VisualStudioautomaticallycreatesaDISCOfilewhenyoucreateaWebServiceproject. Thisfilehasatypeof.vsdiscoandisstoredinthemainapplicationvirtualdirectory (alongwiththe.asmxfile).Asanexample,yourCTempWebServiceprojectcontainsa filenamedCTemp.vsdisco.Thisfilecontainslinkstotheresourcesthatdescribethe CTempWebService.

PublishingwithUDDI

DiscoveryofWebServicesviaDISCOissufficientifyouknowtheURLtotheWebserverortheapplicationvirtualdirectorythathoststheWebService.However,incaseswherethisinformationisunavailable,youmustuseamoregeneralizedsearchtool.UniversalDescription,Discovery,andIntegration(UDDI)enablesaWebServiceconsumertosearchforandlocateWebServices,eveniftheconsumerisunawareoftheexactlocation,owner,orauthorofthoseWebServices.

UDDIistoWebServiceswhatLycosandAltaVistaaretoWebpages.UDDIhelps consumerslocateWebServicesbasedonalogicallycentralized,globallyavailable registryofbusinessesaccessibleviatheInternet.UDDIconsistsoftwobasicparts:

AnXMLschemathatdescribesandcategorizesabusinessandtheWebServicesthatitoffers.

Thebusinessregistry(ordatabase)thatcontainsallknowninformation aboutbusinessesandWebServicesbasedontheXMLschema.

Chapter49:FindingWebServices

FindingWebServiceswiththediscotoolThe.NETFrameworkprovidesatoolnameddisco.exetolocateWebServicesata givenURLandcopytheWebServicedescriptionsthatitfindstoyourlocalharddrive. Theoutputofthediscotoolistypicallyusedasinputtothewsdltooltocreateaproxy classwithwhichtoconsumetheWebService.Thegeneralformatofthediscocommandlineis

disco[options]URLHere,URLspecifiestheHTTPaddressofthetargetWebserverthatyouwanttosearch fordiscovery(.disco)documents.Thediscotoolsupportsthecommand-lineoptionslistedinTable4 9 - 1 .Table49-1:DiscoToolCommand-LineOptions

Option Description/d[omain]:domain Specifiesthe domain nametouse when connecting toaproxy serverthat requires

authentication.

/nosave The discovered documents orresults (.wsdl,.xsd,.disco, and.discomapfiles)arenot savedto disk.The defaultisto savethese documents.

/nologo Suppresses

FindingWebServiceswithUDDIWhilethediscotoolisaneffectivemeansoflocatingWebServicedescriptions,it requiresyoutoknoweithertheURLtoaspecifictargetserverwheretheWebServiceis deployedortheURLtoaspecificWebServicevirtualdirectoryonaWebserver.Inany case,youwon'tbeabletofindanyWebServicesusingdiscowithoutknowingaURL.

Asmentionedpreviously,UDDIisamoregeneralizedsearchtoolforlocatingWeb Services.UsingUDDI,youcanspecifysearchtermsthatallowyoutopinpointWeb Servicesyouwanttousebasedoncompany,industry,servicetypes,andmanyother classifications.Usingthesemoregeneralizedsearchterms,UDDIcanreturninalistof URLswithinformationaboutspecificWebServices,includingtheWSDLdocumentthat youaresearchingfor.

InthemiddleofthepageistheAdvancedSearchform.Fromhere,youcanentertextin theSearchFortextboxtoperformacustomsearchofvariousfieldswithinthedatabase. YoucanlocateWebServicesinthismannerbysearchinganyoneofthefollowingfield types:

Businessname—Usethisfieldtosearchwithinregisteredbusinessnames.Forexample,youcouldsearchforservicesprovidedbyIBM.

Businesslocation—Usethisfieldtosearchbygeographiclocation.Forexample,youcouldsearchforcompaniesthatprovideservices withintheSt.Louisarea.

Servicetypebyname—Usethisfieldtosearchservicessubmittedbyacompanybytheservicename.

Businessidentifier—Identifiersarepiecesofdatathatareuniqueto anindividualbusiness,suchasthestandardD-U-N-S(r)Number. Thereareseveralstandardidentifiers,aswellascustomones,thata companycanregister.

DiscoveryURL—Providesalocationwithdetailsaboutaparticularentity,suchastheURLtoacompanyWebsiteoraparticularWebService.

GeoWebTaxonomy—Providesastandard,hierarchicalclassification ofgeographiclocationsbywhichtosearch.

NAICSCodes—TheNorthAmericanIndustryClassificationSystem (NAICS)providesastandard,hierarchicalclassificationofbusinesses basedontheproductsorservicestheyprovide.

SICCodes—StandardIndustrialClassification(SIC)providesa standard,hierarchicalclassificationofbusinessesbasedonindustry.

UNSPSCCodes—UniversalStandardProductsandServicesCodes (UNSPSC)providesastandard,hierarchicalclassificationof businessesbasedontheproductsandservicestheyprovide.

ISO3166GeographicTaxonomy—SimilartotheGeoWebTaxonomy,providesastandard,hierarchicalclassificationof businessesbasedongeography.

RealNamesKeyword—RealNamesisakeyword-likename,similartoAOLkeywords,thatisregisteredtoaspecificcompany.

Chapter50:ConsumingWebServicesWeb Service Consumer OverviewAWebServiceconsumerisanyapplicationthatreferencesandusesaWebService.It cantakemanyforms:aclientapplication,aserverapplication,acomponent,oreven anotherWebService.Itdoesnotmatter,aslongasitcancallWebServicesbyusing HTTPandSOAP.

ToconsumeaWebService,youneedtodothefollowing:FindtheWebService.ObtainitsWSDLservicecontract.GenerateaproxyclasswithwhichtocalltheWebService.

Createaninstanceoftheproxyclass.Callthemethodsexposedbytheproxy.

Creating the Web Application ProjectLet'sbeginbyusingVisualStudiotocreatetheprojectfilesforyourWebServiceconsumerapplication:

1. Ifyouhavenotalreadydoneso,startVisualStudionowandchooseNewfromtheFilemenu,andthenchooseProjectfromthe submenu.ThisdisplaystheNewProjectdialogbox,asshownin Figure50 - 1 .

2. IntheNewProjectdialogbox,selecttheVisualBasicProjectsfolderfromthelist of projecttypeson theleftsideof thedialogbox.Then chooseASP.NETWebApplicationfromthe listof templatesonthe rightsideofthedialogbox.

3. Next,typeCTempClientintheProjectNametextbox.Notethat,bydefault,theprojectfilesarelocatedonyourlocalWebserverina virtualfoldernamedCTempClient.

Figure50-1: TheVisualStudioNewProjectdialogbox.4. Afteryouhaveenteredthisinformation,clicktheOKbuttonto

createtheproject.VisualStudioautomaticallycreatestheproject andalloftherelatedprojectfilesnecessarytocreateanASP.NET WebapplicationonyourlocalWebserver.Afteryou'vecreated, loaded,andbuilttheproject,theVisualStudiowindowshould resembleFigure 50 - 2 .

Figure50-2: ASP.NETWebapplicationskeletoninVisualStudio.VisualStudiodisplaystheformdesignersurfaceofthedefaultASP.NETWebForm(namedWebForm1.aspx).Eventually,thisformwilldisplaytheuserinterfaceforrequestingtemperatureconversionsinaWebbrowser.

WhenyoucreateanASP.NETWebapplicationprojectinVisualStudioby usingtheWebapplicationprojecttemplate,aprojectfilestructureiscreatedon thetargetWebserverandaVisualStudioSolutionfileiscreatedonyourlocal computer.ThefileslistedinTable50 - 1areautomaticallycreatedbyVisualStudioandplacedinthefilestructureonthetargetdevelopmentWebserver.

Table50-1:VisualStudioWebApplicationProjectFiles

ProjectFile DescriptionWebform1.aspx Thisfile containsthe form definition,userinterface controls,and soonthat makeupthe

WebForm. WebForm1.aspxisthe defaultname giventothe pageby VisualStudio whentheWeb application projectisfirst created.

WebForm1.aspx.vb Thisfile containsthe code-behind classthat handlesthe eventsand related functionality represented bytheWeb Form.

AssemblyInfo.vb Thisfile contains information aboutthe assemblies withinthe WebService project.

Web.config ThisXMLfile contains ASP.NET application configuration information fortheWeb Service.

Table50-1:VisualStudioWebApplicationProjectFiles

ProjectFile DescriptionGlobal.asax Thisfileis responsible forhandling ASP.NET application- levelevents.

Global.asax.vb Thisfile containsthe code-behind classthat handlesthe ASP.NET application- levelevents. Thisfileis referencedby the Global.asa xfileinits ASP.NET application directive.By default,this filedoesnot appearinthe Solution Explorer.

{projectname}.vbproj Thisfile contains project metadata suchasthe listofproject files,build settings,and

soon.

{projectname}.vbproj.webinfo

Thisfile containsa pointertothe Webserver virtual directorythat hostsyour Web application projectfiles.

{projectname}.vsdisco

Thisfile containsthe links(URLs)tothe discovery (disco) information forthis application.

Building the Web FormNowthatyou'vecreatedthebaseprojectfilesforyourconsumerapplication andaddedaWebReferencetotheCTempWebService-you'rereadytobuild aformthatallowsyoutoentervaluesthatcanbepassedtotheCTempWeb Serviceanddisplaytheresultsafteracallismade.IfthedesignersurfacefortheWebForm1.aspxpageisnotcurrentlydisplayed-clickthetabinthemainwindowareaofVisualStudiocorresponding tothisfile.TheWebFormdesignerallowsyoutodraganddropcontrolsonto thedesignersurfaceandmanipulatetheminaWYSIWYGmanner.

Thisapplicationusesthefollowingcontrols:Twotextboxes-onefortheinputtemperatureandonefortheoutput temperatureTworadiobuttonlists-onetoselecttheinputtemperatureunitsandone toselecttheoutputtemperatureunitsOnecommandbuttontoexecutetheunitsconversion

Draganddropthesecontrolsontothedesignersurfaceoftheform.The controlsareavailableinthecontroltoolboxfromtheleftsideofthemainVisual Studiowindow.Ifthecontroltoolboxisnotvisible-chooseToolboxfromthe Viewmenu.Youshouldbeabletofindthecontrolsthatyouneedwithinthe WebFormssectionofthecontroltoolbox.

Afteryouhaveaddedthecontrolstothedesignersurface-youneedtoset somecontrolproperties.MakesurethePropertieswindowappearsby choosingPropertiesWindowfromtheViewmenu.

FollowthesestepstoinitializethecontrolpropertiesofeachcontrolontheWebForm:

1. Clickoneofthetextboxestoselectit.2. InthePropertieswindow-eraseanytextintheTextpropertyand

changetheIDpropertytotxtInputTemp.Thistextboxallowsthe usertoenteraninputtemperaturevalue.Notethatthetextstoredin theIDpropertyisusedtoreferencethiscontrolwithinyourform codeatruntime.

3. Clicktheremainingtextboxtoselectit.4. InthePropertieswindow-eraseanytextintheTextproperty-

changetheReadOnlypropertytoTrue-andchangetheID propertytotxtOutputTemp.Thistextboxisusedtodisplaythe temperatureconversionvalue.TheReadOnlypropertyprevents usersfrommodifyingthetextinthetextbox(sincethisissettothe appropriatevaluebytheformafterobtainingtheresultsoftheunit conversion).

5. Clickthecommandbuttontoselectit.6. InthePropertieswindow-changetheTextpropertytoConverts

ToandchangetheIDpropertytobtnConvert.Clickingthisbutton executestheunitsconversionbasedonthesettingschosenbytheuserintheothercontrols.TheTextpropertyisusedtodisplaya stringonthefaceofthebutton.

7. Clickoneoftheoptionbuttonliststoselectit.8. InthePropertieswindow-changetheIDpropertyto optFromUnits.Next-

selecttheItemspropertyandclickthe detailsbutton(thebuttonwiththeellipsis).ThisdisplaystheListItem CollectionEditordialogbox-asshowninFigure50 - 6 .

Figure50-6: VisualStudioListItemCollectionEditordialogbox.9. Addtwoentriestothelist:onenamedCelsiuswithavalueofCand

onenamedFahrenheitwithavalueofF.SettheFahrenheititem's SelectedpropertytoTruesothatthisentryisselectedbydefault whentheformisdisplayedforthefirsttime.Whenyouarefinished addingtheoptionbuttonlistitems-closetheListItemCollection EditordialogboxbyclickingtheOKbutton.

10.Clicktheremainingoptionbuttonlisttoselectit.11.InthePropertieswindow-changetheIDpropertytooptToUnits.

Next-selecttheItemspropertyandclickthedetailsbutton.This displaystheListItemCollectionEditordialogboxonceagain.

12.RepeatthestepsyouusedtopopulatetheoptFromUnitsoptionbuttonlist_to_addthevariousoutputunititemsto thislist.You shouldaddoptionsforFahrenheit(valueF)-Celsius(valueC)- Kelvin(valueK)-andRankine(valueR).SettheCelsiusitem'sSelectedpropertytoTruesothatthisentryisselectedbydefault whentheformisdisplayedforthefirsttime.Whenyouarefinished addingtheoptionbuttonlistitems-closetheListItemCollection EditordialogboxbyclickingtheOKbutton.

Afteryouhavecompletedthesesteps- rearrangethecontrolsontheformsothattheyresembletheformlayoutshowninFigure50 - 7 .

Figure50-7: ArrangementofuserinterfacecontrolsontheWebForm.NowthatyouhaveyourWebFormcreatedandinitialized-youarereadyto addthecodetotheformthatcreatesaninstanceoftheCTempproxyclassso youcaninteractwiththeproxyclasstoperformtemperatureunitconversions.

Application Execution ModelTheconsumerapplicationisstartedwhenauserrequeststhemainformofthe application:

1. AuserrequeststhemainformoftheCTempClientapplication,suchashttp://localhost/CTempClient/WebForm1.aspx.2.

TheIISWebserveronlocalhostreceivestherequest(technically,anHTTPGETrequest)andhandsitofftotheASP.NETruntimeforexecutionofthepage(becausetherequested pagehasan.aspxextension).Thishand-offoccursviaanISAPI filterextensionthatisregisteredwithinIIStohandleallofthe ASP.NETfiletypes.3. TheASP.NETruntimecreatesaninstanceofthepageclassthat

representstheWebFormandexecutesthepage.4. ThepageclassgeneratestheHTMLandsendsittothebrowser,

causingtheformtoberenderedintheuser'sbrowserwindow.5. ThepageclassisthendestroyedbytheASP.NETruntimealong

withanyothernecessaryrequestcleanupprocessing.(Remember, HTTPisastatelessprotocol,sothereisnoneedtokeepthepage classaroundaftertheHTMLhasbeentransmittedtotheclient.)

6. TheuserentersinformationintotheformandclickstheConvertTobutton.ThiscausestheformtobepostedbacktotheWebserver.

7. Again,theWebserverhandsofftherequest(technically,anHTTP POSTrequest)totheASP.NETruntime,whichcreatesanew instanceofthepageclassthatimplementstheWebFormand executesthepage.

8. Becausethisisapostbackrequest,theserver-sidebuttoncontrol'sClickeventcodeisexecuted.Recallthatthisiswhereyouadded yourcodetocreateandcalltheCTempWebService.

9. TheClickeventcodecreatesaninstanceoftheCTempWeb Serviceproxyclass.Thisclassinheritsfromthe System.Web.Services.Protocols.SoapHttpClientProtoc olclass.ThisprovidesthefoundationforcommunicatingthemethodrequestandresponseviaSOAPmessagesovertheHTTPtransport.

10.TheClickeventcodenow callsthesynchronousCTempmethod ontheproxyobject,passingtheinputargumentsobtainedfromthe postbackdataoftheform(viaserver-sidecontrolproperties).

11.TheWebServiceproxycallstheInvokemethod,passingalongthe inputarguments.ThismethodserializestheCTempmethodcallinto aSOAPmessagethatmatchesthemethodsignaturedefinedinthe WSDLdocument.TheSOAPmessageisthenaddedtothepayload ofanHTTPrequestanddeliveredtotheWebServiceendpoint(the URLofthe.asmxfile).

12.TheIISWebserverthathoststheCTempWebService(inthisspecificcase,localhost)receivestherequest(technically,a

SOAPPOSTrequest)andhandsitofftotheASP.NETruntimeto executetherequestedpage.13.TheASP.NETruntimedeserializestheSOAPpayloadfromthe

request,createsaninstanceoftheCTempWebService implementationclass,andexecutestheCTempmethod,passingthe inputarguments.

14.Next,theASP.NETruntimetakestheresultoftheCTempmethod callandserializesitintoaSOAPresponsemessage.Thismessage isthenaddedtothepayloadofanHTTPresponseanddelivered backtotheclient(inthiscase,yourproxyclass).

15.TheInvokemethodoftheproxyclassdeserializestheresultfromtheSOAPresponsemessageintoageneric.NETObjecttype.This typeisthenexplicitlycasttothereturndatatypeexpectedbythe caller(inthiscase,aDecimaltemperaturevalue)andreturnedto yourconsumerapplication.

16.TheClickeventcodeinyourconsumerapplicationtakestheresult,convertsittoastringdatatype,andassignstheresulttothe outputtextboxintheWebForm,formattedtotwodecimalplaces. Theeventcodeprocessingisnowcompletedandpageexecution continues.

17.Thepageexecutesthroughitsrenderingphasetogeneratethe HTMLthatis returnedto theuser'sbrowser.Justas before,the pageclassis thentorndownby theASP.NETruntime,andany othercleanupprocessingthatisnecessaryisexecuted.