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A function
is similar to a normal procedure but the main purpose of the
function is to accept a certain input 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 syntax 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.
12.1 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 ton Table 12.1 for types
of command button displayed. The Title argument will display the title of the
message board.
Table 12.1: 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 constants in place of integers for the second argument to
make the programs more readable. In fact, VB6 will automatically shows up a list
of named constants 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 12.2 shows the values, the corresponding
named constant and buttons.
Table 12.2 : 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 12.1
Private Sub Button1_Click(ByVal sender
As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim testmsg As Integer
testmsg = MsgBox("Click to test", 1, "Test message")
If testmsg = 1 Then
MessageBox.Show("You have clicked the OK button")
Else
MessageBox.Show("You have clicked the Cancel button")
End If
End Sub
To make the message box looks more sophisticated, you can add an icon besides
the message. There are four types of icons available in VB2008 as shown in
Table 12.3
Example 12.2
Private Sub Button1_Click(ByVal sender As System.Object,
ByVal e As System.EventArgs) Handles Button1.Click
Dim testMsg As Integer
testMsg = MsgBox("Click to Test", vbYesNoCancel + vbExclamation, "Test Message")
If testMsg = 6 Then
MessageBox.Show("You have clicked the yes button")
ElseIf testMsg = 7 Then
MessageBox.Show("You have clicked the NO button")
Else
MessageBox.Show("You have clicked the Cancel button")
End If End Sub |
The first argument, Prompt, will display the message. The output is as shown below:
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12.2
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. In VB2005, you can use the following format:
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 enter.
- x-position and y-position - the position or
tthe coordinates of the input
box.
However, the format won't work in VB2008
because InputBox is considered a namespace. So, you need to key in the full
reference to the Inputbox namespace, which is
Microsoft.VisualBasic.InputBox(Prompt, Title, default_text, x-position, y-position)
The parameters remain the same.
Example 12.3
Private Sub Button1_Click(ByVal sender As
System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim userMsg As String
userMsg = Microsoft.VisualBasic.InputBox("What is your message?", "Message
Entry Form", "Enter your messge here", 500, 700)
If userMsg <> "" Then
MessageBox.Show(userMsg)
Else
MessageBox.Show("No Message")
End If
End Sub
The inputbox will appear as shown in the
figure below when you press the command button
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