protected override void OnNavigatedTo(NavigationEventArgs e)
 {
     base.OnNavigatedTo(e);
     if (e.NavigationMode == NavigationMode.New)
     {
         String uri = null;
         NavigationContext.QueryString.TryGetValue("uri", out uri);
         var feedVM = new FeedViewModel() { Uri = uri };
         DataContext = feedVM;
     }
     else
     {
         var feedvm=(FeedViewModel)DataContext;
         if(!feedvm.FeedLinks.Any())
             feedvm.LoadFeed();
     }
 }
 protected override void OnNavigatedTo(NavigationEventArgs e)
 {
     base.OnNavigatedTo(e);
     if (e.NavigationMode == NavigationMode.New)
     {
         String uri = null;
         NavigationContext.QueryString.TryGetValue("uri", out uri);
         var feedVM = new FeedViewModel()
         {
             Uri = uri
         };
         DataContext = feedVM;
     }
     else
     {
         var feedvm = (FeedViewModel)DataContext;
         if (!feedvm.FeedLinks.Any())
         {
             feedvm.LoadFeed();
         }
     }
 }