Question

我正在使用prism作为我的Windows Phone 8.1运行时应用程序，我想在后台按下我的代码中编写几个条件，所以即使prism会处理硬件后退按钮流我需要在我的本地页面处理它（在cs页面或视图模型内部，所以我覆盖了我的app.cs页面中的OnHardwareButtonsBackPressed方法，在我的本地页面中，我将分别在onnavigatedto和onnavigatedfrom方法中注册和取消注册硬件backbutton事件并编写我的逻辑，它对我来说很好直到应用程序变为后台，如果我的应用程序进入后台并返回，则注册的硬件后退按钮事件将自动取消注册，从那时起回流不起作用。

//App.cs 

    public sealed partial class App : MvvmAppBase
        {
            public App()
            {
                this.InitializeComponent();
            }

            protected override Task OnLaunchApplicationAsync(LaunchActivatedEventArgs args)
            {
                NavigationService.Navigate("Main", null);
                return Task.FromResult<object>(null);
            }

    #if WINDOWS_PHONE_APP
            protected async override void OnHardwareButtonsBackPressed(object sender, Windows.Phone.UI.Input.BackPressedEventArgs e)
            {
                var currentFrame = Window.Current.Content as Frame;
                var currentView = currentFrame.Content as IView;

                if (currentView != null)
                {
                    var backNavigationVM = currentView.DataContext as IBackNavigation;

                    if ((backNavigationVM == null || backNavigationVM.CanGoBack))
                    {
                        base.OnHardwareButtonsBackPressed(sender, e);
                    }
                    else
                    {
                        e.Handled = true;
                    }
                }
                else
                {
                    e.Handled = true;
                }
            }

    #endif


        }


//My page.xaml

    <storeApps:VisualStateAwarePage
        x:Class="BackButtonWithPrism.Views.SecondPage"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="using:BackButtonWithPrism.Views"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        mc:Ignorable="d"
        Background="{ThemeResource ApplicationPageBackgroundThemeBrush}"
        xmlns:storeApps="using:Microsoft.Practices.Prism.StoreApps"
        xmlns:mvvm="using:Microsoft.Practices.Prism.Mvvm"                                
        mvvm:ViewModelLocator.AutoWireViewModel="True">

        <Grid>
            <TextBlock Text="SecondPage" FontSize="{StaticResource TextStyleLargeFontSize}" HorizontalAlignment="Center"></TextBlock>
            <Grid x:Name="FirstGrid">
                <Button HorizontalAlignment="Center" Content="FirstGrid" Click="Button_Click"></Button>
            </Grid>
            <Grid x:Name="SecondGrid">
                <Button HorizontalAlignment="Center" x:Name="btnSecond" Content="SecondGrid"></Button>
            </Grid>
        </Grid>
    </storeApps:VisualStateAwarePage>


//My page.cs

 public sealed partial class SecondPage : VisualStateAwarePage
    {
        public SecondPage()
        {
            this.InitializeComponent();
            this.NavigationCacheMode = NavigationCacheMode.Required;
        }

        protected async override void OnNavigatedTo(NavigationEventArgs e)
        {
            FirstGrid.Visibility = Visibility.Visible;
            SecondGrid.Visibility = Visibility.Collapsed;

#if WINDOWS_PHONE_APP
            Windows.Phone.UI.Input.HardwareButtons.BackPressed += HardwareButtons_BackPressed;

#endif
        }


#if WINDOWS_PHONE_APP
        private async void HardwareButtons_BackPressed(object sender, Windows.Phone.UI.Input.BackPressedEventArgs e)
        {

            if (FirstGrid.Visibility == Visibility.Collapsed)
            {
                e.Handled = true;
                FirstGrid.Visibility = Visibility.Visible;
                SecondGrid.Visibility = Visibility.Collapsed;
            }
            else
            {
                Frame currentFrame = Window.Current.Content as Frame;
                if (currentFrame == null)
                {
                    return;
                }
                else if (currentFrame.CanGoBack)
                {
                    currentFrame.GoBack();
                    e.Handled = true;
                }
            }
        }
#endif

        protected async override void OnNavigatedFrom(NavigationEventArgs e)
        {

            Windows.Phone.UI.Input.HardwareButtons.BackPressed -= HardwareButtons_BackPressed;

        }

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            FirstGrid.Visibility = Visibility.Collapsed;
            SecondGrid.Visibility = Visibility.Visible;
        }


    }


//My Page ViewModel:


public class SecondPageViewModel : ViewModel, IBackNavigation
{
    public bool CanGoBack
    {
        get;
        set;
    }
}

这里我的所有逻辑都写在我的cs页面而不是在viewmodel中写入但是我以后会这样做。

Answer 1

您的问题与OnNavigatedFrom()实施有关。当应用程序被停用并进入后台时，将调用此方法，从而导致后退按钮处理程序的注销。不幸的是，当激活应用程序时，不会调用OnNavigatedTo()来配对它。相反应该处理另一个事件 - Window.Activated。如果您不想将代码复杂化很多，只需尝试将后续处理程序包裹移除以下条件。当应用程序转到后台时，会传递Forward具有当前页面类型的请求。

if (e.NavigationMode != NavigationMode.Forward || e.SourcePageType != GetType())
{
    HardwareButtons.BackPressed -= ...
}

最后一个提示。当你在IDE中放置一个断点并启动调试器应用程序永远不会被挂起，永远不会收到相应的事件。要模拟它们（即激活，暂停和终止），请检查here或here。

当我的应用程序转到windows phone 8.1 app

1 个答案: