WPF TreeView SelectedItemChanged called twice

How to avoid WPF TreeView SelectedItemChanged being called twice
Very often, we need to execute some code in SelectedItemChanged depending on the selected TreeViewItem. But SelectedItemChanged is called twice. This is due to stealing focus from the main window, which is screwing something up.

What we have to do to avoid this is simply delay the call to our code, i.e., MyFunction() which we need to execute in SelectedItemChanged. Here's a workaround which delays the call to open the new window until the item selection code finishes up:

private delegate void NoArgDelegate();

void Window1_SelectedItemChanged(object sender, RoutedPropertyChangedEventArgs<object> e)
{
  Dispatcher.BeginInvoke(DispatcherPriority.Background, 
        (NoArgDelegate)delegate { MyFunction(); });
}