Lesson 10 - VB Built-in Functions

12:48 AM | Posted by Unknown |
A function is similar to a normal procedure but the main purpose of the function is to accept a certain input from the user and return a value which is passed on to the main program to finish the execution. There are two types of functions, the built-in functions (or internal functions) and the functions created by the programmers.

The general format of a function is

     FunctionName (arguments)

The arguments are values that are passed on to the function.

In this lesson, we are going to learn two very basic but useful internal functions of Visual basic , 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  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. In fact, 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 successful" will be displayed and when he/she clicks on the Cancel button, the message "Testing fail" will be displayed.

Figure 10.2

 
To make the message box looks more sophisticated, you can add an icon besides the message. There are four types of icons available in VB as shown in  Table 10.3


Table 10.3





Value
 Named Constant
Icon 



16
 vbCritical





32
 vbQuestion





48
 vbExclamation





64
 vbInformation




Example 10.2
You 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
In this example, the following message box will be displayed:


Figure 10.3

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 by 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.
Example 10.3
i.  The Interface

Figure 10.4
ii. 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.
Labels:
Related Posts Plugin for WordPress, Blogger...

CHATBOX

Translate

Download Installer

Filter Post Here...