WPF - DispatcherUnhandledException does not seem to work

Question

I started a new WPF project in VS2008 and then added some code to trap DispatcherUnhandledException. Then I added a throw exception to Window1 but the error is not trapped by the handler. Why?

   public App()
    {
        this.DispatcherUnhandledException += new DispatcherUnhandledExceptionEventHandler(App_DispatcherUnhandledException);

    }

    void App_DispatcherUnhandledException(object sender, DispatcherUnhandledExceptionEventArgs e)
    {
        System.Windows.MessageBox.Show(string.Format("An error occured: {0}", e.Exception.Message), "Error");
        e.Handled = true;
    }

 void Window1_MouseDown(object sender, MouseButtonEventArgs e)
    {
        throw new NotImplementedException();
    }

Answer 1

Look at following msdn link http://msdn.microsoft.com/en-us/library/system.windows.application.dispatcherunhandledexception.aspx Following is Relevant here

If an exception is not handled on either a background user interface (UI) thread (a thread with its own Dispatcher) or a background worker thread (a thread without a Dispatcher), the exception is not forwarded to the main UI thread. Consequently, DispatcherUnhandledException is not raised. In these circumstances, you will need to write code to do the following:

1. Handle exceptions on the background thread.
2. Dispatch those exceptions to the main UI thread.
3. Rethrow them on the main UI thread without handling them to allow DispatcherUnhandledException to be raised.