UWP中的导航问题

Question

tl; dr

我有3页MainPage.xaml，BlankPage1.xaml，BlankPage2.xaml，Button上的CC_4和BlankPage1分别导航到BlankPage1和BlankPage2。我启用了系统返回按钮，以便可以返回上一页。

Button在MainPage上点击BlankPage1，然后Button点击BlankPage1导航到BlankPage2。这很好。

问题：当我在BlankPage2上点击Back Button时，它返回到BlankPage。现在，当我在BlankPage1上点击Button时，它将转到BlankPage2，但是当我点击Back Button时，而不是转到BlankPage1，它直接导航到MainPage。

下面是我的代码。

mainpage.xaml

<Page
    x:Class="App2.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:App2"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d">
    <Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
        <Button Content="GoTo Page 1" HorizontalAlignment="Center" VerticalAlignment="Center" Tapped="Button_Tapped"/>
    </Grid>
</Page>

mainpage.xaml.cs

using Windows.UI.Xaml.Controls;
namespace App2
{
    public sealed partial class MainPage : Page
    {
        public MainPage()
        {
            this.InitializeComponent();
        }
        private void Button_Tapped(object sender, Windows.UI.Xaml.Input.TappedRoutedEventArgs e)
        {
            Frame.Navigate(typeof(BlankPage1));
        }
    }
}

blankpage1.xaml

<Page
    x:Class="App2.BlankPage1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:App2"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d">
    <Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
        <Button Content="GoTo Page 2" HorizontalAlignment="Center" VerticalAlignment="Center" Tapped="Button_Tapped"/>
    </Grid>
</Page>

blankpage1.xaml.cs

using Windows.UI.Core;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Navigation;
namespace App2
{
    public sealed partial class BlankPage1 : Page
    {
        public BlankPage1()
        {
            this.InitializeComponent();
        }
        protected override void OnNavigatedTo(NavigationEventArgs e)
        {
            if (Frame.CanGoBack)
            {
                SystemNavigationManager.GetForCurrentView().AppViewBackButtonVisibility = AppViewBackButtonVisibility.Visible;
                SystemNavigationManager.GetForCurrentView().BackRequested += (s, a) =>
                {
                    if (Frame.Content.GetType() == typeof(BlankPage1))
                    {
                        if (Frame.CanGoBack)
                        {
                            Frame.GoBack();
                            a.Handled = true;
                        }
                    }
                };
            }
            else
            {
                SystemNavigationManager.GetForCurrentView().AppViewBackButtonVisibility = AppViewBackButtonVisibility.Collapsed;
            }
        }
        private void Button_Tapped(object sender, Windows.UI.Xaml.Input.TappedRoutedEventArgs e)
        {
            Frame.Navigate(typeof(BlankPage2));
        }
    }
}

blankpage2.xaml

<Page
    x:Class="App2.BlankPage2"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:App2"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d">
    <Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
        <TextBlock Text="Final Page" HorizontalAlignment="Center" VerticalAlignment="Center" />
    </Grid>
</Page>

blankpage2.xaml.cs

using Windows.UI.Core;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Navigation;
namespace App2
{
    public sealed partial class BlankPage2 : Page
    {
        public BlankPage2()
        {
            this.InitializeComponent();
        }
        protected override void OnNavigatedTo(NavigationEventArgs e)
        {
            if (Frame.CanGoBack)
            {
                SystemNavigationManager.GetForCurrentView().AppViewBackButtonVisibility = AppViewBackButtonVisibility.Visible;
                SystemNavigationManager.GetForCurrentView().BackRequested += (s, a) =>
                {
                    if (Frame.Content.GetType() == typeof(BlankPage2))
                    {
                        if (Frame.CanGoBack)
                        {
                            Frame.GoBack();
                            a.Handled = true;
                        }
                    }
                };
            }
            else
            {
                SystemNavigationManager.GetForCurrentView().AppViewBackButtonVisibility = AppViewBackButtonVisibility.Collapsed;
            }
        }
    }
}

Answer 1

每次导航到页面时，都会调用OnNavigatedTo方法，并且您正在为BackRequested事件注册一个新处理程序，这意味着当您按下后面时，它将多次执行按钮。您应该在每个页面的OnNavigatedFrom中取消订阅该事件。

设置Handled = true并不意味着无法执行该事件的其他订阅，而只是表示：

如果您不将事件标记为处理的事件，则该系统决定是否远离应用程序（在移动设备系列上）或忽略事件（在台式设备系列上）。

Answer 2

在@decade月亮的答案上构建，我建议您甚至可以将逻辑集中到App类中，以更容易的可管理性和清洁器Page COD-BEHINDS。

。

将以下行添加到App.OnLaunched方法：

SystemNavigationManager.GetForCurrentView().BackRequested += App_BackRequested;

并这样实现处理程序：

private void App_BackRequested(object sender, BackRequestedEventArgs e)
{
    var frame = ( Frame )Window.Current.Content;
    if ( frame.CanGoBack )
    {
        frame.GoBack();
        e.Handled = true;
    }
}

我们抓住当前窗口的框架，并检查是否可以浏览。如果有可能，我们处理事件并导航。这样的优点是，您现在可以删除所有页面上的所有BackRequested相关操作。

您也可以为AppViewBackButtonVisibility做类似的事情：将以下内容添加到OnLaunched的末尾：

rootFrame.Navigated += RootFrame_Navigated;

现在将处理程序实现为：

private void RootFrame_Navigated(object sender, NavigationEventArgs e)
{
    var frame = (Frame)Window.Current.Content;
    SystemNavigationManager.GetForCurrentView().AppViewBackButtonVisibility =
        frame.CanGoBack ? AppViewBackButtonVisibility.Visible :
                          AppViewBackButtonVisibility.Collapsed;            
}

每次框架导航时，后退按钮的可见性将自动更新。