Redirecting an initial navigation

One more post on the subject of keeping screens out of the backstack. A common scenario we see is a variation of the login screen scenario I mentioned the other week. In this case, the first page the user is supposed to see depends on some state saved in by the application (maybe a user preference for which screen to see first, or maybe based on trial mode, etc.) and whilst you want that first page to be in the back stack (ie, it is a legitimate place) you don’t want any additional “landing pages” taking up a slot in the backstack. Another situation where this arises is if your application is extending the Music + Videos hub or is registered as a Photo Extension and you need to show a different page when launched from these experiences.

There are (at least) two ways of doing this; I’ll present two of them here along with a sample app that shows them in action. For my simple example, the trigger for showing a particular page is going to be whether the current time has an even or odd number of seconds (this is a silly example, but makes it easy to test both startup cases). In a real application the trigger might be based on incoming parameters, settings stored in IsoStore, etc.

Cancelling Navigation
The first way to change your initial page is to cancel the incoming navigation to MainPage.xaml and then fire off the desired navigation instead. This is easily done in a few lines of code; firstly, at the end of the App constructor we add an event handler to the Navigating event:

 RootFrame.Navigating += new NavigatingCancelEventHandler(RootFrame_Navigating);

In the event handler, we do several things. First, we check if the navigation is to MainPage.xaml (the NavigationPage specified in the WMAppManifest.xml file) and if not, we bail:

 // Only care about MainPage
 if (e.Uri.ToString().Contains("/MainPage.xaml") != true)
   return;

Read more: Peter Torr's Blog

Posted via email from .NET Info