Lesson 10: Introduction to VB Functions- Part I

Functions are similar to normal procedures but the main purpose of the functions is to accept certain inputs and pass them on to the main program to finish the execution. They are two types of function, the built-in functions(or internal functions) and the functions created by the programmers.

The general format of a function is


functionName(arguments)

where arguments are values that are passed on to the functions.

In this lesson, we are going to learn two very basic but useful internal functions, i.e. the MsgBox( ) and InputBox ( ) functions.
10.1 MsgBox ( ) Function
The objective of MsgBox is to produce a pop-up message box and prompt the user to click on a command button before he /she can continues. This message box format is as follows:

yourMsg=MsgBox(Prompt, Style Value, Title)


The first argument, Prompt, will display the message in the message box. The Style Value will determine what type of command buttons appear on the message box, please refer Table 10.1 for types of command button displayed. The Title argument will display the title of the message board.

Table 10.1: Style Values


Style Value Named Constant Buttons Displayed
0
vbOkOnly Ok button
1
vbOkCancel Ok and Cancel buttons
2
vbAbortRetryIgnore Abort, Retry and Ignore buttons.
3
vbYesNoCancel Yes, No and Cancel buttons
4
vbYesNo Yes and No buttons
5
vbRetryCancel Retry and Cancel buttons

We can use named constant in place of integers for the second argument to make the programs more readable. Infact, VB6 will automatically shows up a list of names constant where you can select one of them.

example: yourMsg=MsgBox( "Click OK to Proceed", 1, "Startup Menu")

and yourMsg=Msg("Click OK to Proceed". vbOkCancel,"Startup Menu")

are the same.

yourMsg is a variable that holds values that are returned by the MsgBox ( ) function. The values are determined by the type of buttons being clicked by the users. It has to be declared as Integer data type in the procedure or in the general declaration section. Table 10.2 shows the values, the corresponding named constant and buttons.

Table 10.2 : Return Values and Command Buttons
Value
Named Constant Button Clicked
1
vbOk Ok button
2
vbCancel Cancel button
3
vbAbort Abort button
4
vbRetry Retry button
5
vbIgnore Ignore button
6
vbYes Yes button
7
vbNo No button

Example 10.1

i. The Interface:

You draw three command buttons and a label as shown in Figure 10.1

Figure 10.1

ii. The procedure for the test button:

Private Sub Test_Click()
Dim testmsg As Integer
testmsg = MsgBox("Click to test", 1, "Test message")
If testmsg = 1 Then
Display.Caption = "Testing Successful"
Else
Display.Caption = "Testing fail"
End If

End Sub

When a user click on the test button, the image like the one shown in Figure 10.2 will appear. As the user click on the OK button, the message "Testing sucessful" will be diplayed and when he/she clicks on the Cancel button, the message "Testing fail" will be displayed.

Figure 10.2

You could draw the same Interface as in example 10.1 but modify the codes as follows:

Private Sub test2_Click()
Dim testMsg2 As Integer
testMsg2 = MsgBox("Click to Test", vbYesNoCancel + vbExclamation, "Test Message")
If testMsg2 = 6 Then
display2.Caption = "Testing successful"
ElseIf testMsg2 = 7 Then
display2.Caption = "Are you sure?"
Else
display2.Caption = "Testing fail"
End If

End Sub

10.2 The InputBox( ) Function

An InputBox( ) function will display a message box where the user can enter a value or a message in the form of text. The format is

myMessage=InputBox(Prompt, Title, default_text, x-position, y-position)

myMessage is a variant data type but typically it is declared as string, which accept the message input bu the users.The arguments are explained as follows:

• Prompt - The message displayed normally as a question asked.
• Title - The title of the Input Box.
• default-text - The default text that appears in the input field where users can use it as his intended input or he may change to the message he wish to key in.
• x-position and y-position - the position or the coordinate of the input box.

The procedure for the OK button

Private Sub OK_Click()
Dim userMsg As String
userMsg = InputBox("What is your message?", "Message Entry Form", "Enter your messge here", 500, 700)
If userMsg <> "" Then
message.Caption = userMsg
Else
message.Caption = "No Message"
End If

End Sub

When a user click the OK button, the input box as shown in Figure 10.5 will appear. After user entering the message and click OK, the message will be displayed on the caption, if he click Cancel, "No message" will be displayed.