Microsoft Visual Basic 2010 Step by Step eBook

244 Part II Programming Fundamentals

Using the Exit Try syntax, you can jump completely out of the current Try or Catch code

block. If there’s a Finally code block, this code will be executed, but Exit Try lets you jump

over any remaining Try or Catch statements you don’t want to execute.

The following sample routine shows how the Exit Try statement works. It first checks to

see whether the Enabled property of the PictureBox1 object is set to False, a flag that

might indicate that the picture box isn’t ready to receive input. If the picture box isn’t yet

enabled, the Exit Try statement skips to the end of the Catch code block, and the file load

operation isn’t attempted.

Try

If PictureBox1.Enabled = False Then Exit Try

PictureBox1.Image = _

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

Catch

Retries += 1

If Retries <= 2 Then

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

Else

MsgBox("File Load feature disabled")

Button1.Enabled = False

End If

End Try

The example builds on the last error handler that you experimented with in this chapter

(the Disc Drive Handler project). If you’d like to test the Exit Try statement in the context of

that program, open the Disc Drive Handler project and enter the If statement that contains

the Exit Try in the Code Editor. You’ll also need to use the Properties window to disable the

picture box object on the form (in other words, to set its Enabled property to False).

Congratulations! You’ve learned a number of important fundamental programming

techniques in Visual Basic, including how to write error handlers. Now you’re ready to

increase your programming efficiency by learning to write Visual Basic modules and

procedures.

Chapter 9 Quick Reference

To Do this

Detect and process

run-time errors

Build an error handler by using one or more Try... Catch code blocks.

For example, the following error handler code tests for path or disc drive

problems:

Try

PictureBox1.Image = _

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

Catch

MsgBox("Check path or insert disc")

Finally

MsgBox("Error handler complete")

End Try