Microsoft Visual Basic 2010 Step by Step eBook

Chapter 9 Trapping Errors by Using Structured Error Handling 235

Use Finally to display a message box

1. Display the Button1_Click event procedure, and then edit the Try... Catch code block so
   that it contains two additional lines of code above the End Try statement. The complete
   error handler should look like this:

Try

PictureBox1.Image = _

System.Drawing.Bitmap.FromFile("d:\fileopen.bmp")

Catch

MsgBox("Please insert the disc in drive D!")

Finally

MsgBox("Error handler complete")

End Try

The Finally statement indicates to the compiler that a final block of code should be

executed whether or not a run-time error is processed. To help you learn exactly how

this feature works, I’ve inserted a MsgBox function to display a test message after

the Finally statement. Although this simple use of the Finally statement is helpful for

testing purposes, in a real program you’ll probably want to use the Finally code block

to update important variables or properties, display data, or perform other cleanup

operations.

2. Remove the CD or DVD from drive D, and then click the Start Debugging button to run
   the program.


3. Click the Check Drive button.

The error handler displays a dialog box asking you to insert the disc in drive D.

4. Click OK.

The program executes the Finally clause in the error handler, and the following message

box appears:

5. Click OK, insert the disc in drive D, and then click the Check Drive button again.

The file appears in the picture box as expected. In addition, the Finally clause is

executed, and the “Error handler complete” message box appears again. As I noted

earlier, Finally statements are executed at the end of a Try... Catch block whether or

not there’s an error.

6. Click OK, and then click the Close button on the form to stop the program.