SSIS OnError Event Handler - How to Retrieve Error Information (Number, Description, Source)

Now that I've figured it out it seems obvious, but I had to struggle a little when creating my first OnError event handler in SQL Server 2005 SSIS. I couldn't figure out how to access the error information that triggered the event. Here's how:

Method A: Expose With the Script Task Editor

You can use the ReadOnlyVariables field on the Script Task Editor to expose these three variables:
ErrorCodeError
Description
SourceName

Then you can read these values from the Dts.Variables collection. Don't use the @ symbol in front of the variable name. To list multiple variables for ReadOnlyVariables, separate them by a comma.

Method B: Get them through code
Some people may prefer to not us ReadOnlyVariables since it creates an dependency external to the script code itself. You can retrieve this variables programatically, but like my LockOneForWrite example it takes some verbose code. Here's some example code I'm using, which uses an extra procedure in the script to retrieve the system variables:

Public Sub Main()
'Assume success
Dts.TaskResult = Dts.Results.Success
Try
Dim errNumber As Integer
Dim errDescription As String
Dim errSource As String

GetErrorValues(errNumber, errDescription, errSource) System.Windows.Forms.MessageBox.Show( _
errNumber.ToString() + vbNewLine + vbNewLine + _
errDescription + vbNewLine + vbNewLine + _
errSource)

Catch ex As Exception
' Displaying the error since this is an example.
System.Windows.Forms.MessageBox.Show(ex.ToString())
End Try

End Sub

Private Sub GetErrorValues(ByRef errNumber As Integer, _
ByRef errDescription As String, ByRef errSource As String)

Try
Dim vars As Variables
Dts.VariableDispenser.LockForRead("ErrorCode")
Dts.VariableDispenser.LockForRead("ErrorDescription")
Dts.VariableDispenser.LockForRead("SourceName")
Dts.VariableDispenser.GetVariables(vars)

Try
errNumber = CType(vars("ErrorCode").Value, Integer)
errDescription = vars("ErrorDescription").Value.ToString()
errSource = vars("SourceName").Value.ToString()

Catch ex As Exception
Throw ex
Finally
vars.Unlock()
End Try
Catch ex As SystemException
Throw ex
End Try
End Sub

Notice how the GetErrorValues() procedure returns the error information via ByRef arguments. Feel free to copy the code.