ADV_GIS VB - III 1

Advanced GIS:functions,Procedures, Arrays

and Collections

Fall 2003

ADV_GIS VB - III 2

Functions and subprocedures Functions - consist of code that does something

specific and then return a value to the part of the program that called it. For example, the Sin() function.

Subprocedures - don’t return results, eg. the “Unload” method. So far, the code we wrote are for event subprocedures. When a command button named “Command1” is pressed, Visual Basic runs the Command1_Click() event subprocedure. Subprocedure usually does something, like changing the display, but it doesn’t tend to pass anything back to Visual Basic

ADV_GIS VB - III 3

Creating a sub procedure

Two ways to add sub procedure 1) Use the Add Procedure dialog box or

Open the Code Editor window and go to Tools > Add Procedure. Type in Name of the procedure and make sure Private scope is checked and click OK to continue

2) Directly define a procedure in the Code Editor window - type in code for a procedure and end with End Sub

ADV_GIS VB - III 4

Call Procedure Using “Call Procedure_Name” to call procedure. You may

directly use Procedure without calling procedures, but it’s not recommended.

Private Sub cmdCalculate_Click()

intMyNumber = InputBox (“Input your number”)

Call SquareNumber

End Sub

Private Sub mnuToolsCalculate_Click()

SquareNumber

End Sub

Private Sub SquareNumber()

lblAnswer.Caption = intMyNumber * intMyNumber

End Sub

ADV_GIS VB - III 5

Passing Arguments to procedures

Private Sub SquareNumber(intNum As Double)

lblAnswer.Caption = intNum * intNum

End Sub

Private Sub cmdCalculate_Click()

intMyNumber = InputBox (“Input your number”)

Call SquareNumber(intMyNumber)

End Sub

Exercise: create a sub procedure with two arguments for calculating area of a rectangle

Private Sub Area(x as single, y as single)

lblAnswer.Caption = x * y

End Sub

Private Sub cmdCalculate_Click() ‘need to declare width/height

width = Inputbox (“Input width of a square”)

height = inputbox (“Input height of a square)

Call Area(width, height)

End Sub

ADV_GIS VB - III 6

Let’s create a window menu using Menu EditorAdd a new form (Project

> Add Form)Go to Tools > Menu

Editor and create a two-layer menu as shown on right

ADV_GIS VB - III 7

Common Dialogs

Insert Common Dialogs from Project > Component > Microsoft Common Dialog

The following are the functions available: Open file- ShowOpen Save File - ShowSave Color - ShowColor Font - ShowFont Print - ShowPrinter Help - ShowHelp

Name this common dialog as “dlgFile”

ADV_GIS VB - III 8

Connect File>Save with Common DialogIn Code Editor, type in the following code

associated with mnuFileSave_Click()dlgFile.ShowSave

ADV_GIS VB - III 9

Exercise Add Two menus to your SlideShow(HW8) program: File and Tools Add Save As, and Exit on File menu and SlideShow on Tools

menu. (mnuFile, mnuFileSaveAs - Ctrl+S, mnuFileExit, mnuTools, mnuToolsSlideShow)

Add Microsoft Common Dialog Control 6.0 and name it as “dlgMain” (under munFileSaveAs_Click() )

dlgMain.FileName = lstSlides.Text

dlgMain.ShowSave

If dlgMain.FileName <> “” Then

SavePicture imgPicture, dlgMain.FileName

End If ‘SavePicture requires two arguments, first-the picture or image

control from which the graphic file is to be created. The second is the full path to the location where the picture file is to be saved.

ADV_GIS VB - III 10

use code “Unload Me” for mnuFileExit (and dlgFile.ShowOpen to associate with Open, if Open is under File)

mnuToolsSlideShow_Click() - type a msgbox “SlidShow has not been implemented yet” with vbExclaimation

run this program and save file to different location with different file names

ADV_GIS VB - III 11

Public or Private

Public subprocedures are declared like this Public Sub <subprocedure name>

Public Function <function name> As <return type>

A public routine can be accessed throughout the program but a private can only called in the same Form or Module

Advantage of using Privateuse less memory, code protected within one corner,

and names used over and over

ADV_GIS VB - III 12

Passing arguments to procedures If a procedure requires arguments, they are passed to the

procedure, when the procedure is called. Let’s create a Sub called SquareNumber with argument and one command button, one text box and a label for showing the answer.

Private Sub SqureNumber (intNum As Double) lblAnswer.Caption = intNum * intNum

End Sub Arguments have to be supplied to run this procedure. Let’s

modify cmdCalculate

Private Sub cmdCalculate_Click()

Call SquareNumber (txtNum.text)

End Sub

ADV_GIS VB - III 13

ByRef or ByVal Argument s can be passed either by value or by reference.

Passing by value- a copy of the variable is passed to the sub procedure. If the variable is changed in the sub procedure, the original variable in the calling procedure is not affected. If an argument is passed by reference, changing the argument in the sub procedure will permanently change the argument in the calling procedure. ByRef is default, if not specified

Dim X As Integer

X = 5

Call aSub(X)

MsgBox “X = “ & X

Private Sub aSub (ByVal Y As Integer)

Y = 6

End Sub

Try ByRef

Change ByVal to ByRef and see the differences

ADV_GIS VB - III 14

Built-in functions String, numeric, date and time, financial functions. Commonly used String functions

LCase/UCase: converts to L/U case Len: return length of string Left/Right/Mid: return specified number of cha. form

left/right/middle side of a string. Replace: replace one or more occurrence of a string inside

another LTrim/RTrim/Trim: removes spaces from the beginning (end)

(both ends) of a string. InStr/InStrRev: returns the position of the first(last) occurrence of

one string within another Join: return a string created by joining a number of substrings

contained in an array.

ADV_GIS VB - III 15

Numeric/Date/Time

Abs/Sin/Cos/Tan/Atn(arctangent)/Exp/Log/ Sqr/Sgn(sign of a number)/Rnd (random number)/Int,Fix (integer portion of a number)

Date-current system dateDateAdd- add specified interval to a dateDateDiff - differ of two specified dates....

ADV_GIS VB - III 16

Variable Scope

Type Declaration Where ScopeLocal Dim varName as VarType In each event or Subprocedure only used in procedure

Dim myVariable as Integer in which they are declared

Private Private varName as varType in (General) (Declarations) used in all procedures Dim varName as varType section of the form or module in that module

Public(Global) Public varName as varType in (General)(Declarations) used in all modules in the section of a code module only whole project

Static Static varName as varType in any location Scope depends on whereit is declared.Data is preserved out ofscope

ADV_GIS VB - III 17

Static statement - to preserve the values of procedure-level variables, use Static VariableName [As data type]

used to maintain the values of variables between calls of the procedure.

Try thisPrivate Sub Command1_Click()

Static intNum As Integer intNum = intNum + 1 MsgBox intNum

End Sub

Try to run these code several times, the increment ofintNum can be shown in Static but not Dim

Private Sub Command1_Click()Dim intNum As IntegerintNum = intNum + 1MsgBox intNum

End Sub

ADV_GIS VB - III 18

Option Explicit

Implicit Declaration - in VB, if no declaration for variables. Try the following code

myVariable = 5myVariable = myVariable + 5MsgBox myVariable

ADV_GIS VB - III 19

Function procedures - return values which determines data type of functions

Return a value from a function by assigning it to the name of the function itself. Basically, the function is treated as though it were a variable.

In slides 4/5, the SqureNumber sub can only change the lblAnswer.Caption. If a function is in place such as the follows:

Private Function SqureNumber (intNum As Double) As Double

SquareNumber = intNum * intNum

End FunctionPrivate Sub munToolsCalcualte_Click()

Dim intMyNumber As Double

intMyNumber = txtNum.Text

lblAnswer.Caption = SqureNumber (intMyNumber)

End Sub

ADV_GIS VB - III 20

Multi-form projects Most projects need more than one form. For instance, login

form, splash form and about form. To add a new form to a project, choose Add Form from the

Project menu or right-click in the Project Explorer window. Form can be referred as “Me” by procedures within the form,

and other forms must be referred to by their names. If a project contains more than one form, a startup form must

be declared in the Project Properties dialog box, accessed from the Project menu. (go to Project>Project Properties...)

If you want the application to start without any form initially loaded (e.g., retrieve data ->display one of the form depending on the contents of the data file), then create a Sub procedure called Main in a standard module and select Sub Main as the Startup Object.

ADV_GIS VB - III 21

Manage FormsTasks Methods/Statements

Load/Not Display Load Statement

Load&Dispaly Show method

Display a loaded form Show method

Hide/Not unload Hide method

Hid&Unload Unload

Load frmMain ‘ or frmMain.Show

frmMain.Hide ‘ or Me.Hide

Unload frmMain ‘or Unload Me, code portions still exist

Set frmMain = Nothing ‘completely terminate the form and ‘reclaim memory

ADV_GIS VB - III 22

Modal/Modeless Forms Most of dialog boxes in VB are modal. Only one form can be

modal on the screen at one time. When a modal form is displayed, the application beeps if the user clicks outside the form.

Modeless form- allows the user to switch to another form or dialog box

With the style argument vbModal or vbModeless, the Show method displays a modal or modeless form. If you do not specify the style argument, the form will be modeless. For example:

‘Modal form frmMain.Show vbModal ‘Modeless form, the default frmMain.Show vbModeless

ADV_GIS VB - III 23

Standard modules

No GUI, no form, only code. Public procedures shared by multiple projects, avoid

referencing form-specific controls, which can be passed as arguments to the general procedures of the standard module.

To call the procedure from outside the standard module, directly refer to procedure’s name, if it is unique, otherwise, you need the module name as the prefix. To call procedure within own std module, simply refer to the procedure name.

Save the std module with a unique name and .bas file extension in the same directory where the project file is saved.

ADV_GIS VB - III 24

Practice Create a new project with form. Add standard module from U:\4850_5850\ArcObjects\

aml_func.bas by checking on Project>Add Module and navigate to this directory.

Add a command button(cmdParse, Caption:Parse), textbox (txtInput) and type in code under cmdParse_Click()

Private Sub cmdParse_Click()

Dim strMyArray() As String

ParseStringR txtInput.Text, strMyArray

MsgBox strMyArray(0)

End Sub ‘try single quote

ADV_GIS VB - III 25

Arrays - used to store a series of elements that usually contain related information

Fixed-size arrayDynamic arrayMulti-dimensional arrays

ADV_GIS VB - III 26

1-D fixed array

Dim My1DFixedArray(4) As String ‘declare array with 5 elements

My1DFixedArray(0) = “Heart” ‘assign value

My1DFixedArray(1) = “Club”

My1DFixedArray(2) = “Spade”

My1DFixedArray(3) = “Diamond”

My1DFixedArray(4) = “Club”

MsgBox My1DFixedArray(2) ‘retrieve

‘Specify upper/lower bound

Dim My1DFixedArray(0 to 4) As String

Dim My1DFixedArray(1 to 4) As String

ADV_GIS VB - III 27

Dynamic Arrays - number of elements to be stored is not known ahead of time

Dim DynArray() As String

Dim X As Integer

X = InputBox (“Enter the number of elements in the_ array: “)

ReDim DynArray(X-1)

Slide1 Slide2 Slide3 Slide4 .... ....

0 1 2 3

Allow programmer to manage memory more efficiently than fixed arrays

ADV_GIS VB - III 28

ReDim/Preserve/Erase

The size of array will be specified at run-time with keyword ReDim and the memory for the array is then allocated. You can change size of dynArray anytime with ReDim statements, but the original values contained in array are lost once encountering ReDim. Use keyword “Preserve” to preserve values.

ReDim Preserve DynArray (UBound(DynArray) + 1) ‘this add one element more but preserve previous values

Use “Erase” to deallocate memory and ReDim to reallocate memory. e.g Erase DynArray

ADV_GIS VB - III 29

Multi-dimensional arrays

Path(0) Date(1) Second(2)Title(3)

Slide(0) C:\temp 1/30/89 5 Slide show

Slide(1) U:\4850 3/19/02 4 Rex

Slide(2) E:\temp 3/20/01 6 Trees

Option ExplicitDim Slide() As StringPrivate Sub Command1_Click()ReDim Slide(0 to 3, 0 to 1)‘Assign value Slide(col,row) = valueSlide(0,0) = “C:\temp”Slide(0,1) = “1/30/89”Slide(0,2) = “5”Slide(0,3) = “Slide Show”Slide(1,0) = “U:\4850”

‘Add more data ReDim Preserve Slide(3, UBound (Slide,2) + 1)

ADV_GIS VB - III 30

Exercise - work with 2-D dynamic arrays

Create a new Form(frmGrades, “Enter Grades”), add two labels(lblStudentName, “Student Name”; lblLetterGrade, “Letter Grade”), 2 text (txtStudent, “”; txtGrade, “”), 1 commandbox (cmdApply, “Apply Grade”, Default = True), Horizontal Scroll Bar (hscStudent, Max=0, Min=0)

The application will store students’ names and grades in any array (dynamic). Because the values in the array will need to be used in 2 different procedures. Variables have to be declared at the form level. Dim Score() As String

Store student names in a 2-D dynamic array: Declare a Static variable Number As Integer (maintain the number of students between procedure calls)

ADV_GIS VB - III 31

GradePrivate Sub cmdApply_Click()

Static Number As Integer

ReDim Preserve Score(1, Number)

Score(0, Number) = txtStudent.Text

Score(1, Number) = txtGrade.Text

hscStudent.Max = Number

hscStudent.Value = Number

Number = Number + 1

End Sub

Private Sub hscStudent_Change()

txtStudent.Text = Score(0, hscStudent.Value)

txtGrade.Text = Score(1, hscStudent.Value)

End Sub

2-D Array txtStudent.text stored in Score’ first column, and txtGrade in 2nd column

hscStudent.Value: indicate where the slider of the horizontal scroll bar is located and act as the index for the Score array. When you move the scroll bar slider, the Value property is changed, and a different element in the Score array is retrieved and displayed in txtStudent

ADV_GIS VB - III 32

Collection -an object that does not have a graphic component, dynamically grows and shrinks

Dim MyCollection As New Collection You can use four methods: Add, Remove, Count, and

Item (Variant is the data type for storing different data type)

Key MyCollectioin

“Hello” 3.14159 2/7/02 Slide1

Index

Key

1 2 3 4

“strHello” “Pi” “dt2/7/02” “slide1”

It’s safer to use the key strings to identify the items, why?

ADV_GIS VB - III 33

Colleciton - 2 ‘Add NewItem w/o key at the end of the collection MyCollection.Add NewItem ‘Add NewItem w/ key “myNewItem” at the end of the col. MyCollection.Add NewItem “myNewItem” Remove using Index or Key. Index starts from 1 not 0. MyCollection.Remove 5 ‘Remove the fifth item MyCollection.Remove “myNewItem” ‘remove using key To Change an item, add new item first before or after the old item,

then remove the old one. e.g. change 2/7/02 to 3/20/02 MyCollection.Add “3/20/02”, “dt3/20/02”,3 MyCollection.Remove 4 ‘ or Remove dt2/7/02 Set MyCollection = Nothing ‘clear collection

ADV_GIS VB - III 34

Looping through Collection

1) For Each... Next and 2) For....Next

Dim Thing As Variant

For Each Thing In MyCollection ‘ for each is more efficient ‘than for next.

lstName.AddItem Thing

Next

Set Thing = Nothing ‘ set variant to nothing will recollect ‘memory

Dim I As Integer

For I = 1 to MyCollection.Count

lstName.AddItem MyCollection.Item(I)

Next I

ADV_GIS VB - III 35

Homework 9-1: 30 points, due on 11/6/03.

Work on your previous homework, if you don’t have a good vbp file, copy it from data_center\hw9-data folder.

See demo for the tasks to be completed.See link on the webpage to get detailed

description of the homework