Chapter 9 Quick Reference

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
Test for specific error conditions in an event handler	Use the Catch When syntax and the Err.Number property. For example: Try PictureBox1.Image = _ System.Drawing.Bitmap.FromFile _ ("d:\fileopen.bmp") Catch When Err.Number = 53 'if File Not Found MsgBox("Check pathname and disc drive") Catch When Err.Number = 7 'if Out Of Memory MsgBox("Is this really a bitmap?", , _ Err.Description) Catch MsgBox("Problem loading file", , _ Err.Description) End Try
Create your own errors in a program	Use the Err.Raise method. For example, the following code generates a Disc Full error and handles it: Try Err.Raise(61) 'raise Disc Full error Catch When Err.Number = 61 MsgBox("Error: Disc is full") End Try
Write nested Try…Catch error handlers	Place one Try…Catch code block within another. For example: Try PictureBox1.Image = _ System.Drawing.Bitmap.FromFile _ ("d:\fileopen.bmp") Catch MsgBox("Insert the disc in drive D!") Try PictureBox1.Image = _ System.Drawing.Bitmap.FromFile _ ("d:\fileopen.bmp") Catch MsgBox("File Load feature disabled") Button1.Enabled = False End Try End Try
Exit the current Try or Catch code block	Use the Exit Try statement in the Try or the Catch code block. For example: If PictureBox1.Enabled = False Then Exit Try