DetailPage.xaml.cs

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using RssReader.Common;
using RssReader.ViewModels;
using Windows.UI.Core;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Media.Animation;
using Windows.UI.Xaml.Navigation;

namespace RssReader.Views
{

    public sealed partial class DetailPage : Page
    {
        private MainViewModel ViewModel => AppShell.Current.ViewModel;

        public DetailPage()
        {
            InitializeComponent();

            ArticleWebView.NavigationStarting += async (s, e) => 
                await e.LaunchBrowserForNonMatchingUriAsync(ViewModel.CurrentArticle.Link);

            ArticleWebView.LoadCompleted += (s, e) => ArticleWebView.Visibility = Visibility.Visible;
        }

        protected override void OnNavigatedTo(NavigationEventArgs e)
        {
            base.OnNavigatedTo(e);

            if (ViewModel.CurrentArticle != null)
            {
                if (!ViewModel.CurrentArticle.Link.IsEquivalentTo(ArticleWebView.Source))
                {
                    ArticleWebView.Navigate(ViewModel.CurrentArticle.Link);
                }
                else
                {
                    ArticleWebView.Visibility = Visibility.Visible;
                }
            }

            var backStack = Frame.BackStack;
            var backStackCount = backStack.Count;

            if (backStackCount > 0)
            {
                var masterPageEntry = backStack[backStackCount - 1];
                backStack.RemoveAt(backStackCount - 1);

                // Clear the navigation parameter so that navigation back to the 
                // MasterDetail page won't reset the current article selection. 
                var modifiedEntry = new PageStackEntry(
                    masterPageEntry.SourcePageType,
                    null,
                    masterPageEntry.NavigationTransitionInfo
                    );
                backStack.Add(modifiedEntry);
            }

            // Register for hardware and software back request from the system
            SystemNavigationManager systemNavigationManager = SystemNavigationManager.GetForCurrentView();
            systemNavigationManager.BackRequested += DetailPage_BackRequested;
            systemNavigationManager.AppViewBackButtonVisibility = AppViewBackButtonVisibility.Visible;
            ViewModel.IsInDetailsMode = true;
        }

        protected override void OnNavigatedFrom(NavigationEventArgs e)
        {
            base.OnNavigatedFrom(e);

            SystemNavigationManager systemNavigationManager = SystemNavigationManager.GetForCurrentView();
            systemNavigationManager.BackRequested -= DetailPage_BackRequested;
            systemNavigationManager.AppViewBackButtonVisibility = AppViewBackButtonVisibility.Collapsed;
            ViewModel.IsInDetailsMode = false;
            ArticleWebView.Visibility = Visibility.Collapsed;
        }

        private void OnBackRequested()
        {
            // Page above us will be our master view.
            // Make sure we are using the "drill out" animation in this transition.

            if (Frame.CanGoBack) Frame.GoBack(new DrillInNavigationTransitionInfo());
        }

        void NavigateBackForWideState(bool useTransition)
        {
            if (useTransition)
            {
                Frame.GoBack(new EntranceNavigationTransitionInfo());
            }
            else
            {
                Frame.GoBack(new SuppressNavigationTransitionInfo());
            }
        }

        private bool ShouldGoToWideState()
        {
            return Window.Current.Bounds.Width >= 720;
        }

        private void PageRoot_Loaded(object sender, RoutedEventArgs e)
        {
            if (ShouldGoToWideState())
            {
                // We shouldn't see this page since we are in "wide master-detail" mode.
                // Play a transition as we are navigating from a separate page.
                NavigateBackForWideState(useTransition: true);
            }
            Window.Current.SizeChanged += Window_SizeChanged;
        }

        private void PageRoot_Unloaded(object sender, RoutedEventArgs e)
        {
            Window.Current.SizeChanged -= Window_SizeChanged;
        }

        private void Window_SizeChanged(object sender, Windows.UI.Core.WindowSizeChangedEventArgs e)
        {
            if (ShouldGoToWideState())
            {
                // Make sure we are no longer listening to window change events.
                Window.Current.SizeChanged -= Window_SizeChanged;

                // We shouldn't see this page since we are in "wide master-detail" mode.
                NavigateBackForWideState(useTransition: false);
            }
        }

        private void DetailPage_BackRequested(object sender, BackRequestedEventArgs e)
        {
            // Mark event as handled so we don't get bounced out of the app.
            e.Handled = true;

            OnBackRequested();
        }
    }
}