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Server-side Programmingusing
ASP .NET Web Forms
Yingcai Xiao
Part I
Programming the Internet
Programming the Internet
The Internet as a Computer
Every computer on the Internet is a “CPU” Transmitting data/information in a standardized way is
the key
Analogy of Internet Protocols:
IP => “Binary” (low-level Internet transmission protocol)
HTTP => “Assembly” (high-level Internet transmission protocol)
HTML => High Level Language (for writing web-pages)An international language everyone
understand
Internet Protocol IP: Internet Protocol
data transmission protocol (standard) for the Internet.• The Internet is a computer network based on the Internet Protocol. • Each computer on the Internet is identified by its Internet Address:
130.101.10.134 or wp.cs.uakron.edu • Data transmitted between computers on the Internet as packet.• Each packet has an IP header followed by data.• The first 2 entries in an IP header are the receiver’s address and the sender’s
address. IP is similar to postal mailing (Packet Switching), not phoning (Circuit Switching).
• IPv4 (32bit addressing, 4B), IPv6 (48bit addressing, 256T)• The headers are in the standard IP format, platform-independent. • Data (any type) is transmitted over the Internet bit-by-bit. No restrictions on
what can be transmitted.• Binary data are platform-dependent. Binary data transmitted from one
computer to another computer may not be readable by the receiver if it has a different binary data format than the sender.
Hypertext Transfer Protocol Can we make it platform-independent? The World Wide Web is an application built on the Internet using the Hypertext
Transfer Protocol in which only text data is permitted to be transmitted.
HTTP (Hypertext Transfer Protocol) • Tim Berners-Lee ("father of the Web") and RFC 2068
(www.w3.org/Protocols/rfc2068/rfc2068).• Entirely text based: ASCII (8-bits) or Unicode (16-bits).• Platform independent • Defines how Web browsers and Web servers communicate.• 7 instructions defined in HTTP 1.1.: GET, POST, …• Transmitted over TCP/IP (Transport Control Protocol/Internet Protocol).• Web applications are implemented over the Internet using HTML and other
Web languages.
HTML (Hypertext Markup Language) • Defines syntax and semantics of the Web language.• Entirely text based (platform independent)• Hypertexts are tagged in < >, not to be displayed. They are
metadata describing regular text. (http://www.w3schools.com/tags/)
• Browsers are GUI-based HTML interpreters. HTML 4.01 became XHTML 1.0 in 2000
simple.html:<html>
<body>Hello, world
</body></html>
HTML
Client-Side:• Thin client
1. Only a browser is needed.2. The browser renders a html page on the client
computer.3. HTML (static), DHTML (dynamic), HTML5 (dynamic
and multi-medium).4. Programming with embedded scripts: JavaScript, .
Dynamic and computational. 5. Ajax (asynchronous JavaScript & XML):
asynchronous.6. Plugins: VRML (3D Web)7. Java Applet: transmit the application to the client and
run it there. Too much to transmit for large distribution lists.
Computing over the Internet
Client-Side:• Thick client
1. Client program installed prior, no need to download at runtime.
2. Runs like any other program on the client, but can talk to the server when needed.
3. .NET Remoting, Windows Communication Foundation (WCF),
4. Java's Remote Method Invocation (RMI)5. Common Object Request Broker Architecture
(CORBA)
Computing over the Internet
Server-Side:• Web pages are generated by server side programs at
runtime. Dynamic contents and heavy-duty computing.• Server Scripts
1. Perl, PHP, ….2. Does not scale well. (each client needs a process to
service)• Server VMs
1. .NET ASP (Active Server Page), JSP (Java Server Page),
2. All clients are served by a single process. The process will create a thread to serve each client.
Computing over the Internet
Server-Side:• CMS (Content Management Systems): web contents are
managed at server side on demand. • Dejango CMS, Joomla.
Server-Client Communication:• Important for Internet based computing.• HTTP channel (slower, works for both thin and thick
clients).• TCP/IP channel (faster, works only for thick clients).
Computing over the Internet
What happens when browsing a web page on a server?
http://www.wintellect.com/simple.html • Start a client (a browser).• Type in the URL (Unified Resource Locator).• Internet’s Domain Name System (DNS) converts www.wintellect.com into an IP address (66.45.26.25).• The browser opens a socket (IP) connection to the server using default port 80 (mailbox #). http://www.wintellect.com:80/simple.html
What happens when browsing a web page on a server?
• The browser transmits an HTTP request to the server.GET /simple.html HTTP/1.1Accept: */*Accept-Language: en-usAccept-Encoding: gzip, deflateUser-agent: Mozilla/4.0.(compatible; MSIE.6.0; Windows NT 5.1)Host: www.wintellect.comConnection: Keep-Alive[blank line]
What happens when browsing a web page on a server?
• The server transmits an HTTP response back.
HTTP/1.1 200 OKServer: Microsoft-IIS/5.0Date: Wed, 24 Oct 2001 14:12:37 GMTContent-Type: text/htmlAccept-Ranges: bytesLast-Modified: Wed, 24 Oct 2001 14:00:53 GMTETag: "d02acf81975cc11:a78"Content-Length: 46[blank line]<html><body>Hello, world</body>
</html>
What happens when browsing a web page on a server?
• Upon receiving the response, the browser parses the HTML and displays the resulting Web page.
• This is just a static page.• To compute, we need get the data from the client user.
A client form is needed. HTML form serves the purpose.
http://winserv1.cs.uakron.edu/xiaotest/Calc.html<html> <body> <form method=“post”> <input type="text" name="op1" /> + <input type="text" name="op2" /> <input type="submit" value=" = " /> </form> </body></html>
HTML Forms
What’s happening?
No action to send anything to the server when the user types values in the text fields. But when the submit button (<input type=“submit”>) is clicked, the browser submits the form along with any input in the form’s controls. POST /calc.html HTTP/1.1…Content-Length: 11[blank line]op1=2&op2=2
Part II
Server Side Programming
Web Server
Deploying a Web Page on an IIS server.IIS: Internet Information Services
Server: winserv1.cs.uakron.eduDeploying Directory: C:\Inetpub\wwwrootAccess URL: http://winserv1.cs.uakron.edu/ (case insensitive)
Server-Side ProcessingCommon Gateway Interface (CGI)• CGI applications write HTTP responses to standard output (stdout) on the server, which are then forwarded to the client browser.• Defines a low-level programmatic interface between Web servers and applications that run on Web servers. • CGI applications can be written in any programming language. • CGI applications read the input accompanying postbacks through server environment variables and standard input (stdin).• Slow, restarts a process on every request.
ISAPI
ISAPI: Internet Server Application Programming Interface• ISAPI extensions are Windows DLLs hosted by IIS. • They’re referenced by URL just like HTML files (for example, http://www.wintellect.com/calc.dll). • IIS forwards HTTP requests to an ISAPI DLL by calling a special function exported from the DLL. • The DLL generates HTTP responses. • Faster than CGI (run in the same process as IIS). • Once loaded, they remain in memory. • They’re difficult to write.
Active Server Pages (ASP)
Active Server Pages (ASP) Introduced in 1996. Dynamically generates HTML on Web servers. Allows HTML and scripts / languages to be mixed. The embedded script code are between the <% and %> tags. When an Active Server Page is requested, ASP server parses
the page and executes any scripts contained inside it. Scripts access the input by using the Request object. Scripts write HTML to the HTTP response using the Response
object, which is sent to the client by the Web server along with the static HTML.
ASP integrates with ActiveX Data Objects (ADO). Interpreted, slow. Lacks encapsulation.
<%@ Language="VBScript" %><html> <body> <form> <input type="text" name="op1" value="<%= Request ("op1") %>"/> + <input type="text" name="op2" value="<%= Request ("op2") %>" /> <input type="submit" value=" = " /> <% If Request ("op1") <> "" And Request ("op2") <> "" Then a = CInt (Request ("op1")) b = CInt (Request ("op2")) Response.Write (CStr (a + b)) End If %> </form> </body></html>
Calc.asp
Part III
ASP.NET
APS.NETASP: Microfoft’s equivalent of JSPCode on the server that dynamically generates HTML for the clients at runtime.
JSP: Java Server PageJava code on the server that generates HTML for the clients.HTML contents can be dynamically generated at runtime
ASP.NET: ASP based on the .NET framework, one of the most popular web programming techniques. Code on the server that dynamically generates HTML for the clients at runtime.
ASP.NET
WEB
SERVER
IIS
WEB
CLIENT
Application 3
Application 2
Application 1
ASP.NET
HTTP
Web Forms
Web Forms are GUI-based EDP (Event Driven Programming) web pages built
around controls and event handlers. .NET web forms are processed on the server side. Web forms use HTML, HTTP and IP to transmit and display GUI into a client
web-browser.
ASP.NET Web Forms• GUI for Web applications• Object-oriented (encapsulation, inheritance, polymorphism)• Event driven (EDP)• Server-side processing (dynamic generation of HTML)• Compiled code, faster• HTML embedding tag: <asp: \>
(processed on the server side)• File extension: .aspx• To deploy on winserv1:
copy Examples/c5/calc.aspx to C:\Inetpub\wwwroot\xiaotest
• To access: http://winserv1.cs.uakron.edu/xiaotest/calc.aspx
ASP.NET Web Forms
<html> <body> <form RunAt="server"> <asp:TextBox ID="op1" RunAt="server" /> + <asp:TextBox ID="op2" RunAt="server" /> <asp:Button Text=" = " OnClick="OnAdd" RunAt="server" /> <asp:Label ID="Sum" RunAt="server" /> </form> </body></html><script language="C#" RunAt="server"> void OnAdd (Object sender, EventArgs e) { int a = Convert.ToInt32 (op1.Text); int b = Convert.ToInt32 (op2.Text); Sum.Text = (a + b).ToString (); }</script>
Calc.aspx
When Calc.aspx is accessed by a clientAn ASP.NET server page contains two parts: static HTML code and dynamic embedded APS.NET code.
ASP.NET-enabled web server processes the ASP.NET code in the server page. (Tomcat does not support ASP.NET but Mono does)
It instantiates TextBox, Button, and Label objects (the classes are defined in System.Web.UI.WebControls). Each object dynamically renders itself into HTML.
The dynamically generated HTML is merged into the static HTML.
The resulting HTML is returned to the client as an HTTP response.
Calc.aspx as seen by the client<html> <body> <form name="_ctl0" method="post"
action="calc.aspx" id="_ctl0"> <input type="hidden" name="__VIEWSTATE" value="dDwxOTE0NDY4ODE2Ozs+" /> <input name="op1" type="text" id="op1" /> + <input name="op2" type="text" id="op2" /> <input type="submit" name="_ctl1" value=” = " /> <span id="Sum"></span> </form> </body></html>
note: there are also “hidden” and “div” (section) tags.
• When the “ = “ button is clicked, the input from “op1” and “op2” are posted to the server and directed to calc.aspx (since action="calc.aspx"). • On the server side, ASP.NET notifies the Button object in calc.aspx and the Button responds by firing a Click event. • ASP.NET receives the event and subsequently invokes its handler: OnAdd ( ).• “Sum.Text = (a + b).ToString ();” renders the result into the
“Sum” label in <span id="Sum"></span> as HTML.• The dynamically generated HTML is merged with the static HTML (parts not in server side tags). • The resulting HTML is sent to the client browser.
Use the client browser’s View->Page Source menu to see the final HTML code received by the client. (Mac: Tools->Web Developer->Page Source)
When Calc.aspx is accessed by a client
ASP.NET Controls
Two types: Web Controls and HTML Controls
Web Controls• Class names are prefixed with asp:. • Classes are from System.Web.UI.WebControls.• The name of the object is defined by the ID attribute. • ASP Web controls are rendered into HTML. • ASP Web controls are highly programmable.
They support methods, properties, events.
<asp:TextBox Text="2" ID="op1" runat="server" />
This web control initializes the textbox to display 2. Any public property of a control can be used this way.
ASP.NET Controls
• Control properties can be accessed from server-side scripts (code between the <script> and </script> tags). Read a control property by scripts:
int a = Convert.ToInt32 (op1.Text);Write a control property by scripts:
Sum.Text = (a + b).ToString ();
• Event-driven programming. Controls fire events when users click on them. Wiring an event to an event handler is accomplished by prefixing the event name with “On”. <asp:Button Text=" = " RunAt="server" OnClick="OnAdd" />
• Exception handling can be added in the handlers.void OnAdd (Object sender, EventArgs e){ try {
int a = Convert.ToInt32 (op1.Text); int b = Convert.ToInt32 (op2.Text); Sum.Text = (a + b).ToString (); }
catch (FormatException) { Sum.Text = “Format Error";
}}
ASP.NET Controls
Three principles of the Web Forms programming model:• A Web form’s user interface is “declared” using a combination of HTML and server controls. • Server controls fire events that can be handled by server-side scripts. • Server-side scripts in ASP.NET are compiled to CIL and executed by the CLR on the server.RunAt=“server” must be used in every tag that ASP.NET is to process
The Web Forms Programming Model
Web Controls
AdRotator Displays rotating banners in Web
forms
Button Generates submit buttons
Calendar Displays calendars with selectable dates
CheckBox Displays a check box in a Web form
CheckBoxList Displays a group of check boxes
CompareValidator Validates user input by comparing it to another value
CustomValidator Validates user input using the
algorithm of your choice
Web Controls
DataGrid Displays data in tabular format
DataList Displays items in single-column or multicolumn lists using HTML
templates
DropDownList Generates HTML drop-down lists
HyperLink Generates hyperlinks
Image Displays images in Web forms
ImageButton Displays graphical push buttons
Label Generates programmable text fields
LinkButton Generates hyperlinks that post back to the server
Web Controls
ListBox Generates HTML list boxes
Literal Generates literal text in a Web form
Panel Groups other controls
RadioButton Displays a radio button in a Web form
RadioButtonList Displays a group of check boxes
RangeValidator Verifies that user input falls within a
specified range
RegularExpressionValidator Validates user input using regular
expressions
Repeater Displays items using HTML templates
Web Controls
RequiredFieldValidator Verifies that an input field isn’t empty
Table Generates HTML tables
TextBox Generates text input fields
ValidationSummary Displays a summary of validation errors
Xml Displays XML documents and optionally formats them using XSLT
ASP.NET HTML controls mimic the original HTML tags. (They are processed on the server side. They are not HTML tags which are processed by the client browser.)e.g. <input type="text" RunAt="server" />• HTML controls are used like HTML tags.• An HTML control is an instance of System.Web.UI.HtmlControls.HtmlInputText. • ASP.NET sees the RunAt=“server” attribute and creates an HtmlInputText object. • The HtmlInputText object, in turn, emits an <input type=“text”> tag that’s ultimately returned to the browser.• HTML controls (server side) have properties and can generate events which make them more powerful than HTML tags (client side). Without RunAt="server“, HTML controls become HTML tags.
HTML Controls
HTML Controls
Tag Corresponding HTML Control
<a runat=“server”> HtmlAnchor
<button runat=“server”> HtmlButton
<form runat=“server”> HtmlForm
<img runat=“server”> HtmlImage
<input type=“button” runat=“server”> HtmlInputButton
<input type=“reset” runat=“server”> HtmlInputButton
<input type=“submit” runat=“server”> HtmlInputButton
HTML Controls
<input type=“checkbox” runat=“server”>
HtmlInputCheckBox
<input type=“file” runat=“server”> HtmlInputFile
<input type=“hidden” runat=“server”> HtmlInputHidden
<input type=“image” runat=“server”> HtmlInputImage
<input type=“radio” runat=“server”> HtmlInputRadioButton
<input type=“password” runat=“server”>
HtmlInputPassword
<input type=“text” runat=“server”> HtmlInputText
<select runat=“server”> HtmlSelect
HTML Controls
<table runat=“server”> HtmlTable
<td runat=“server”> HtmlTableCell
<th runat=“server”> HtmlTableCell
<tr runat=“server”> HtmlTableRow
<textarea runat=“server”> HtmlTextArea
Any other tag with runat=“server” HtmlGenericControl
<html> <body> <form runat="server"> <input type="text" id="op1" runat="server" /> + <input type="text" id="op2" runat="server" /> <input type="submit" value=" = " OnServerClick="OnAdd" runat="server" /> <span id="Sum" runat="server" /> </form> </body></html>
<script language="C#" runat="server">void OnAdd (Object sender, EventArgs e){ int a = Convert.ToInt32 (op1.Value); int b = Convert.ToInt32 (op2.Value); Sum.InnerText = (a + b).ToString (); }</script>
The HTML controls version of Calc.aspx
Part IV
ASP.NET Internals
When ASP.NET processes the first HTTP request for an ASPX file:1. It creates class representing the dynamic code of the file.2. It compiles it, loads it, creates an object for it.3. The object initializes itself and processes page-level events. 4. The object generates HTML output to be sent to the client. 5. The object remains in the server memory to process further
requests to the page.6. When the ASPX file is modify, ASP.NET automatically repeats
steps 1-4.
How does an ASP.NET enabled server process an ASPX file?
When ASP.NET processes the first HTTP request for an ASPX file:1. It creates a Page class deriving from class System.Web.UI.Page. 2. It copies the code in the ASPX file to the Page-derived class. 3. A method (e.g. OnAdd) in a <script> block becomes a member method of the derived class.4. ASP.NET compiles the derived class and places the resulting
DLL in a system folder and caches it there. C:\WINNT\Microsoft.NET\Framework\vn.n.nnnn\Temporary ASP.NET Files.5. ASP.NET instantiates an object of the derived Page class and “executes” it by calling a series of methods on it. 6. The Page object instantiates any controls declared inside it and solicits their output.
How does a ASP.NET enabled server process an ASPX file?(Details)
7. As the Page object executes, it fires a series of events (page-level events) that can be processed by server-side scripts: “Init”, which is fired when the page is first instantiated, and “Load”, which is fired after the page’s controls are initialized but before
the page renders any output. 8. Implicit wiring of Page events to handlers by defining handlers’ names as
Page_EventName.
<asp:DropDownList ID="MyList" RunAt="server" /> . . .<script language="C#" runat="server"> void Page_Load (Object sender, EventArgs e) { if (!IsPostBack) { // if it is not from the client for (int i=0; i<5; i++) {// list 5 days DateTime date = DateTime.Today + new TimeSpan (i, 0, 0, 0); MyList.Items.Add (date.ToString ("MMMM dd, yyyy")); } } } </script>
Page-Level Events
ASP.NET Compilation Directives @
@ Page Defines general attributes and compilation settings for ASPX files (e.g. Language)
@ Control Defines general attributes and compilation settings for ASCX files
@ Import Imports a namespace
@ Assembly Enables linkage to assemblies, not linked to by default
@ Register Registers user controls and custom controls for use in a Web form
@ OutputCache Exerts declarative control over page caching and fragment caching
@ Reference Adds a reference to an external ASPX or ASCX file
@ Implements Identifies an interface implemented by a Web page
Must be positioned at the top of an ASPX file.
1. ASPX files are in text files, anyone can read it.2. When a company sells its ASPX server programs, it does not want
people to see their source code.3. How? Code-behind is designed to protect the source code.4. For the static code in HTML, we can’t do anything about it.5. Dynamic code in C# or other .NET languages can be separated out
and compiled into DLLs.6. Only the static HTML code and the DLLs are delivered to the
customs.
Separating Static Code from Dynamic Code
1. Create a CS file (e.g. Examples/C5/Lander/Lander.cs) containing code that would normally appear between <script> and </script> tags. Make each of these source code elements members of a class (e.g. LanderPage) derived from System.Web.UI.Page.
2. In your Page-derived class, declare protected fields whose names mirror the IDs of the controls declared in the ASPX file (e.g. Lander.aspx). At run time, ASP.NET maps these fields to the controls of the same name.
3. Compile the CS file into a DLL.In a Visual Studio Command Prompt window, run the following: csc /target:library Lander.cs
Code-behind with C#
4. Place the HTML portion of the Web form—everything between the <html> and </html> tags—in an ASPX file (e.g. Lander.aspx).
5. Include in the ASPX file an @ Page directive containing an Inherits attribute that identifies the Page-derived class in the DLL. When a request arrives for that page at run-time, ASP.NET derives a child class from this class to create the form.e.g. <%@ Page Inherits="LanderPage%>
6. To use the source code without recompiling: <%@ Page Inherits="LanderPage" Src="Lander.cs" %>
7. Code embedded has to be in C#, VB .NET, or JScript. Code-behind can be in any other language supported by .NET.
Code-behind in Web forms coded in C#
8. To deploy the program: move the ASPX file to
Inetpub/wwwroot/xiaotest/Lander and the DLL to Inetpub/wwwroot/xiaotest/Lander/bin.
9. The program can be accessed the same way as other ASP.NET programs:
http://winserv1.cs.uakron.edu/xiaotest/Lander/Lander.aspx9. In order for
http://winserv1.cs.uakron.edu/xiaotest/Lander/Lander.aspx to work, the Lander directory has to be converted to a Web Application, which instructs ASP.NET to find Lander.dll under the application’s bin directory.
Code-behind in Web forms coded in C#
Create a Web Application in IIS
* You need to be an administrator to use IIS
winserv1 -> Sites -> Default Web Site Right-click->Add Application Alias: xiaotestLander Application pool: defualtAppPool Physical path: C:\inetpub\wwwroot\xiaotest\Landerhttp://winserv1.cs.uakron.edu/xiaotest/Lander/Lander.aspx
Existing directories can be converted to Web Applications• winserv1 -> Sites -> Default Web Site->xiaotest• Right-click on Lander• Convert to Application • Application pool: defualtAppPool• http://winserv1.cs.uakron.edu/xiaotest/Lander/
Lander.aspx
Development of Web forms using Visual Studio .NET• Create a Web Application project• Use forms designer to design forms by drag-and-drop controls from a palette onto the forms.• Edit the HTML.• Write event handlers by double-clicking controls and filling
in empty method bodies.• Compile and run applications by executing simple menu commands.
Web Forms and Visual Studio .NET
Summary
Web Programming, Client Side, Server Side, HTTP, HTML, HTML Forms, CGI, ISAPI, ASP, ASP.NET, ASP.NET Forms, ASP.NET Controls, IIS, Web Forms Programming Model, Page-Level Events, Code Behind.
Principles: What are they? How do they work? (internals, static structures, dynamic
data/event flow.) Practice:
Explain the logic, output, and internal working of a given code segment.
Find errors in a given code segment.Write a simple program to perform a given task.
