protected override IObservable<Unit> OnNavigatedToAsync(NavigatedInfo e)
 {
     if (!this.ViewModel.IsDataLoaded)
     {
         this.ViewModel.LoadData();
     }
      	         return base.OnNavigatedToAsync(e);
 }
 /// <summary>
 /// Invoked when the Page is loaded and becomes the current source of a parent Frame.
 /// </summary>
 /// <param name="e">
 /// Event data that can be examined by overriding code. The event data is representative
 /// of the pending navigation that will load the current Page. Usually the most
 /// relevant property to examine is Parameter.
 /// </param>
 /// <returns></returns>
 protected virtual IObservable<Unit> OnNavigatedToAsync(NavigatedInfo e)
 {
     return completed;
 }
 internal IObservable<Unit> OnNavigatedToInternalAsync(ReactiveShell shell, NavigatedInfo e)
 {
     this.RegisterAppBars();
     return OnNavigatedToAsync(e);
 }