MessageBox.Show in App Closing/Deactivated events

Question

I have a MessageBox being shown in Application Closing/Deactivated methods in Windows Phone 7/8 application. It is used to warn the user for active timer being disabled because

Answer 1

Register BackKeyPress event on RootFrame.

RootFrame.BackKeyPress += BackKeyPressed;
private void BackKeyPressed(object sender, CancelEventArgs e)
    {
        var result = (MessageBox.Show("Do you want to exit XXXXX?", "Application Closing", MessageBoxButton.OKCancel));
        if (result == MessageBoxResult.Cancel)
        {
            // Cancel default navigation
            e.Cancel = true;
        }
}