RootVisual is null when returning from Tombstoning?

Question

Hi I just found out that my application was crashing when returning from tombstoning. I was able to target the problem here inside the constructor of my page:

RadPhoneApplicationFrame frame = App.Current.RootVisual as RadPhoneApplicationFrame;
frame.PageTransitionCompleted += 
                         new EventHandler<EventArgs>(frame_PageTransitionCompleted);

Everytime the app is Re-Activated the RootVisual is setting the frame to null. I'm wondering if there is a casting issue here because before I used this code my tombstoning was working perfectly and I was able to navigate freely throughout the app. Any ideas on what might be causing this? Or maybe a work around?

Answer 1

You should move this code from page constructor to OnNavigatedTo method override in your page. Reason is that RootVisual is probably set in RootFrame.Navigated event handler which is generated after page is constructed, not before (this depends of implementation in your App.xaml.cs).

Of course because OnNavigatedTo method may be runned more that once for a page, you should make sure that PageTransitionCompleted event handler is not assigned two times (just use -= before +=).

Another option is to move this code to App.xaml.cs. This makes sense most to me, because that PageTransitionCompleted event is related to whole app, not a single page.