c# - 逻辑删除时恢复应用程序状态的默认页面

Question

我想知道是否有任何方法可以在应用程序中将页面状态恢复到墓碑后的标准页面。例如，如果应用程序在用户位于第 2 页时被逻辑删除，则恢复的页面将始终是第 1 页。我对如何从我的应用程序的第 2 页恢复数据有疑问，我认为此方法是克服此问题的替代方法问题。

public FeedPage()
{
    InitializeComponent();
    this.Loaded += new RoutedEventHandler(FeedPage_Loaded);
    performanceProgressBar.Visibility = System.Windows.Visibility.Collapsed;
    LoadFeed();
}

private void LoadFeed()
{
    FrameworkElement root = Application.Current.RootVisual as FrameworkElement;
    var currentFeed = root.DataContext as FeedViewModel;
    WebClient client = new WebClient();
    performanceProgressBar.IsIndeterminate = true;
    performanceProgressBar.Visibility = System.Windows.Visibility.Visible;
    client.DownloadStringCompleted += new DownloadStringCompletedEventHandler(client_DownloadStringCompleted);
    client.DownloadStringAsync(new Uri(currentFeed.FeedUrl)); 
    this.DataContext = currentFeed;
    ApplicationBar.IsVisible = false;    
}

...

private void FeedPage_Loaded(object sender, RoutedEventArgs e)
{
    if (!App.ViewModel.IsDataLoaded)
    {
        App.ViewModel.LoadData();
    }
}

我的问题是我现在不知道如何在 tobstone 时存储 currentFeed。每次应用程序被激活时，currentFeed 为空。我尝试了很多解决方案但没有结果。

public partial class App : Application
{
    private static MainViewModel viewModel = null;

    /// <summary>
    /// A static ViewModel used by the views to bind against.
    /// </summary>
    /// <returns>The MainViewModel object.</returns>
    public static MainViewModel ViewModel
    {
       get
        {
            // Delay creation of the view model until necessary
            if (viewModel == null)
                viewModel = new MainViewModel();

            return viewModel;
        }

    }


    /// <summary>
    /// Provides easy access to the root frame of the Phone Application.
    /// </summary>
    /// <returns>The root frame of the Phone Application.</returns>
    public PhoneApplicationFrame RootFrame { get; private set; }

    /// <summary>
    /// Constructor for the Application object.
    /// </summary>
    public App()
    {
        // Global handler for uncaught exceptions. 
        UnhandledException += Application_UnhandledException;

        // Show graphics profiling information while debugging.
        if (System.Diagnostics.Debugger.IsAttached)
        {
            // Display the current frame rate counters.
            Application.Current.Host.Settings.EnableFrameRateCounter = true;

            // Show the areas of the app that are being redrawn in each frame.
            //Application.Current.Host.Settings.EnableRedrawRegions = true;

            // Enable non-production analysis visualization mode, 
            // which shows areas of a page that are being GPU accelerated with a colored overlay.
            //Application.Current.Host.Settings.EnableCacheVisualization = true;
        }

        // Standard Silverlight initialization
        InitializeComponent();

        // Phone-specific initialization
        InitializePhoneApplication();
    }

    // Code to execute when the application is launching (eg, from Start)
    // This code will not execute when the application is reactivated
    private void Application_Launching(object sender, LaunchingEventArgs e)
    {
    }

    // Code to execute when the application is activated (brought to foreground)
    // This code will not execute when the application is first launched
    private void Application_Activated(object sender, ActivatedEventArgs e)
    {
    }

    // Code to execute when the application is deactivated (sent to background)
    // This code will not execute when the application is closing
    private void Application_Deactivated(object sender, DeactivatedEventArgs e)
    {
    }

    // Code to execute when the application is closing (eg, user hit Back)
    // This code will not execute when the application is deactivated
    private void Application_Closing(object sender, ClosingEventArgs e)
    {

    }


    // Code to execute if a navigation fails
    private void RootFrame_NavigationFailed(object sender, NavigationFailedEventArgs e)
    {
        if (System.Diagnostics.Debugger.IsAttached)
        {
            // A navigation has failed; break into the debugger
            System.Diagnostics.Debugger.Break();
        }
    }

    // Code to execute on Unhandled Exceptions
    private void Application_UnhandledException(object sender, ApplicationUnhandledExceptionEventArgs e)
    {
        if (System.Diagnostics.Debugger.IsAttached)
        {
            // An unhandled exception has occurred; break into the debugger
            System.Diagnostics.Debugger.Break();
        }
    }

    #region Phone application initialization

    // Avoid double-initialization
    private bool phoneApplicationInitialized = false;

    // Do not add any additional code to this method
    private void InitializePhoneApplication()
    {
        if (phoneApplicationInitialized)
            return;

        // Create the frame but don't set it as RootVisual yet; this allows the splash
        // screen to remain active until the application is ready to render.
        RootFrame = new PhoneApplicationFrame();
        RootFrame.Navigated += CompleteInitializePhoneApplication;

        // Handle navigation failures
        RootFrame.NavigationFailed += RootFrame_NavigationFailed;

        // Ensure we don't initialize again
        phoneApplicationInitialized = true;
    }

    // Do not add any additional code to this method
    private void CompleteInitializePhoneApplication(object sender, NavigationEventArgs e)
    {
        // Set the root visual to allow the application to render
        if (RootVisual != RootFrame)
            RootVisual = RootFrame;

        // Remove this handler since it is no longer needed
        RootFrame.Navigated -= CompleteInitializePhoneApplication;
    }

    #endregion
}

这是我的 app.xaml.cs，现在没有任何更改。使用此代码，tombstone 在主页和详细信息页面中可以正常工作，但(当然)在 feed 页面中不能正常工作。

Answer 1

查看 App.xaml.cs 中的以下方法:

private void Application_Deactivated(object sender, DeactivatedEventArgs e)

private void Application_Activated(object sender, ActivatedEventArgs e)

这是您应该在独立存储中保存和加载状态数据的地方。

这也是您可以强制应用导航到另一个页面的地方，但我强烈建议不要这样做。用户不期望这种行为，也许你甚至不会在市场上发布。这一点也不难，您所要做的就是在这些方法中加载和保存您的状态。

到目前为止，您尝试做什么？问题到底出在哪里？