1. Introduction to Error Handling
...or how to keep from shooting ourselves in the foot!

2. Using Un-Structured Error Handling
On Error Goto

3. Creating an Error Handler
Private Sub btnSave_Click...
On Error GoTo MyErrHandler
FileOpen (1, “FileName”, OpenMode.Output)
‘more code here
Exit Sub
MyErrHandler:
MsgBox (“The following error occurred: “, err.Description)
End Sub

4. Using Structured Error Handling
Try
Catch
Finally
End Try

5. A Simple Error Trap File.Open(1, txtFileName.Text, FileMode.Open) Try
‘read the file
Catch exp As Exception ' Will catch any error
MessageBox.Show(exp.Message)
End Try

6. Trapping Multiple Exceptions...
Try
fs = File.Open(Me.txtFileName.Text, FileMode.Open)
fs.Close()
Catch exp As FileNotFoundException
' Will catch an error when the file requested does not exist.
MessageBox.Show("The file you requested does not exist.", Me.Text, MessageBoxButtons.OK)
Catch exp As DirectoryNotFoundException
' Will catch an error when the directory requested does not exist.
MessageBox.Show("The directory you requested does not exist.", Me.Text, MessageBoxButtons.OK)
Catch exp As IOException
' Will catch any generic IO exception.
MessageBox.Show(exp.Message, Me.Text, MessageBoxButtons.OK, MessageBoxIcon.Stop)
Catch exp As Exception
' Will catch any error that we're not explicitly trapping.
End Try

7. Using “Finally” in the Try-Catch Scenario...
fs = File.Open(Me.txtFileName.Text, FileMode.Open)
fs.Close()
Catch exp As FileNotFoundException
' Will catch an error when the file requested does not exist.
MessageBox.Show("The file you requested does not exist.", Me.Text, MessageBoxButtons.OK)
Catch exp As Exception
' Will catch any error that we're not explicitly trapping.
MessageBox.Show(exp.Message, Me.Text, MessageBoxButtons.OK, MessageBoxIcon.Stop)
Finally
‘this always executes
MessageBox.Show("File closed successfully in Finally block", Me.Text, MessageBoxButtons.OK)
End Try

8. Final Decision... If YouAreTired = True Then The End = True Else
GrabACookie = True
End If