private void NextButton_Click(object sender, RoutedEventArgs e)
 {
     if (CreateLunchFrame.SourcePageType.Equals(typeof(FriendsPage)))
     {
         CreateLunchFrame.Navigate(typeof(DateTimePage));
     }
     else if (CreateLunchFrame.SourcePageType.Equals(typeof(DateTimePage)))
     {
         CreateLunchFrame.Navigate(typeof(PlacesPage));
     }
 }
        protected override void OnNavigatedTo(NavigationEventArgs e)
        {
            ViewModel.CreateLunch();
            ViewModel.LunchBeingCreated.Host = ViewModel.User;

            User Invitee = null;

            if (e.Parameter is User)
            {
                Invitee = e.Parameter as User;
            }
            else if (e.Parameter is Restaurant)
            {
                ViewModel.LunchBeingCreated.Location = e.Parameter as Restaurant;
            }

            SystemNavigationManager.GetForCurrentView().BackRequested += CreateLunchPage_BackRequested;
            base.OnNavigatedTo(e);

            CreateLunchFrame.Navigate(typeof(FriendsPage), Invitee);
        }