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.

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.

Example

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.

Creating Your Own Functions The general format of a function is as follows: Public  Function functionName (Arg As dataType,..........) As dataType or Private  Function functionName (Arg As dataType,..........) As dataType * Public indicates that the function is applicable to the whole program and    Private indicates that the function is only applicable to a certain module or procedure.

Example 11.1 In this example, a user can calculate future value of a certain amount of money he has today based on the interest rate and the number of years from now supposing  he will invest this amount of money somewhere .The calculation is based on the compound interest rate.   Public Function FV(PV As Variant, i As Variant, n As Variant) As Variant 'Formula to calculate Future Value(FV) 'PV denotes Present Value FV = PV * (1 + i / 100) ^ n End Function Private Sub compute_Click() 'This procedure will calculate Future Value Dim FutureVal As Variant Dim PresentVal As Variant Dim interest As Variant Dim period As Variant PresentVal = PV.Text interest = rate.Text period = years.Text FutureVal = FV(PresentVal, interest, period) MsgBox ("The Future Value is " & FutureVal) End Sub Example 11.2 The following program will automatically compute examination grades based on the marks that a student obtained.

      In previous lesson, we have programmed a CD player. Now, with some modifications, we will transform the CD player into an audio file player. This player will be created in such a way that it could search for wave and midi files in your drives and play them.

In this project, you need to insert a ComboBox, a DriveListBox, a DirListBox, a TextBox and a FileListBox into your form.I Shall briefly discuss the function of each of the above controls. Besides, you must also insert Microsoft Multimedia Control(MMControl) in your form , you may make it visible or invisible. In my program, I choose to make it invisible so that I could use the command buttons created to control the player.

• ComboBox- to display and enable selection of different type of files.
• DriveListBox- to allow selection selection of different drives available on your PC.
• DirListBox - To display directories
• TextBox - To display selected files
• FileListBox- To display files that are available

Relevant codes must be written to coordinate all the above controls so that the application can work properly. The program should flow in the following logical way:

Step 1: User choose the type of files he wants to play.

Step2:User selects the drive that might contains the relevant audio files.

Step 3:User looks into directories and subdirectories for the files specified in step1. The files should be displayed in the  FileListBox.

Step 4:  User selects the files from the FileListBox and click the Play button.

Step 5: User click on the Stop to stop playing and Exit button to end the application.

The Interface

The Code

Private Sub Combo1_Change()
' to determine file type

If ListIndex = 0 Then
File1.Pattern = ("*.wav")
ElseIf ListIndex = 1 Then
File1.Pattern = ("*.mid")
Else
Fiel1.Pattern = ("*.*")
End If
End Sub

Private Sub Dir1_Change()

'To change directories and subdirectories(or folders and subfolders)

File1.Path = Dir1.Path
If Combo1.ListIndex = 0 Then
File1.Pattern = ("*.wav")
ElseIf Combo1.ListIndex = 1 Then
File1.Pattern = ("*.mid")
Else
File1.Pattern = ("*.*")
End If
End Sub