Why does FocusManager.GetFocusedElement(this) always returns null?

I have an app which runs fine as a simple WPF app having an event handler on GotFocus at the main window level like so :

    private void MainWindowGotFocus(object sender, RoutedEventArgs e)
    {
        var element = FocusManager.GetFocusedElement(this) as FrameworkElement;
        if (element != null)
        {
               //...

However this behaves strangely when set as a XBAP app (almost exactly the same code - the main visual element is Page and not Window but the event is still available and triggered).

In that case (XBAP/wpf browser开发者_如何学C application) element is always null.

Any ideas? :(

Well thanks to a colleague of mine (Bogdan R.) we've discovered that FocusManager.IsFocusScope has different default values for Window (WPF) and Page (XBAP), namely it is false for the latter.

Simply setting FocusManager.IsFocusScope on the Page element fixes the problem.

could also try to use Keyboard.FocusedElement instead