QuickStart: The ErrEx function

The ErrEx function is designed to be used from inside of your global error handling routine as a replacement for the built-in Err function.  It also handles the enabling and disabling of your global error handler and is typically considered the starting point for accessing all the features of the product.

The object that ErrEx returns provides the same properties as Err, but includes these enhancements:

The object that ErrEx returns provides five properties for determining the location of the error:

The ErrEx.State property defines what will happen next after your error handler has finished.

Initially, when your error handler is called, the State property indicates what state the local error handling was in before the error occurred. It can be one of five values:

Primarily this property is used to ignore certain errors. For example, to ignore errors that will be caught by a local error handler, one can write the global error handler like this;

Public Sub MyGlobalErrorHandler()

    If ErrEx.State = OnErrorResumeNext Then Exit Sub
    If ErrEx.State = OnErrorGotoLabel Then Exit Sub
    If ErrEx.State = OnErrorPropagate Then Exit Sub

    LogErrorToFile

    MsgBox "An unhandled error has occurred..." & ErrEx.Description '... etc

End Sub

The State property value can also be altered. For example, for debugging purposes you might wish to disable the use of ‘On Error Resume Next’ in your code to find a bug:

Public Sub MyGlobalErrorHandler()

    If ErrEx.State = OnErrorResumeNext Then ErrEx.State = OnErrorGoto0
    
    '...

End Sub

The valid values for State on output are:

With this functionality, the State property gives you the flexibility to create your own full featured error dialogs. For example, you might want to implement an error dialog for when developing which includes a 'Debug' button, but you probably wouldn't want your end-user clients having these options, so you can implement a different error handler for clients. The Sample.mdb gives you a real example of this scenario and much more.

One of the great features of the Global Error Handler is the customizable Vista-style error dialog. This can be opened using the ErrEx.ShowErrorDialog method. ErrEx.ShowErrorDialog also conveniently returns a value that can be assigned directly to the ErrEx.State property (OnErrorEnd, OnErrorResumeNext, etc)

To open the Vista-style dialog, you can do this:

Public Sub MyGlobalErrorHandler()

    ErrEx.State = ErrEx.ShowErrorDialog()

End Sub

For more details on customizing the Vista-style error dialog, see QuickStart: The Vista-style Error Dialog.

To handle errors locally we need to set the global error handler to ignore error states of OnErrorResumeNext, OnErrorGotoLabel and OnErrorPropagate (i.e. leaving the default VBA compatibility in place).

We also use a feature of ErrEx to pass unhandled local errors back on to the global error handler if we decide not to handle the error in the local handler.

Public Sub MyGlobalErrorHandler()

    Select Case ErrEx.State

	Case OnErrorGoto0, CalledByLocalHandler

            ErrEx.State = ErrEx.ShowErrorDialog

    End Select

End Sub

Public Sub Example()

    On Error Goto MyLocalErrorHandler

    Debug.Print 1/0	' Raise an error
    Exit Sub

MyLocalErrorHandler:
    If Err.Number = 11 ' Division by zero error
        Resume Next
    Else
        ErrEx.CallGlobalErrorHandler    ' Call the global error handler
    End If

End Sub

So now we are handling local errors (division by zero in this example) and also passing any unhandled errors back on to the global error handler.

Tip: To obtain a thorough understanding of this approach, the best advice is to copy the above example code into a VBA application, set a break point on it and step through the code line by line.

For taking this a step further and ensuring that all open objects (e.g. recordsets) are closed when an error occurs, see Demo 2 of the Sample.mdb.