我有Prism和AppShell的UWP应用.
我想在通过BackButton退出之前添加确认对话框.
我尝试了这个：

protected override Task OnLaunchApplicationAsync(LaunchActivatedEventArgs args)
    {
        ...
        SystemNavigationManager.GetForCurrentView().BackRequested += App_BackRequested;

        ...
    }

private void App_BackRequested(object sender, BackRequestedEventArgs e)
    {
        Frame rootFrame = Window.Current.Content as Frame;
        if (rootFrame == null)
        {  
           return;
        }

        if (rootFrame.CanGoBack && e.Handled == false)
        {
            <add confirm dialog here>
            e.Handled = true;
        }
    }

但是rootFrame始终为null,并且如果历史记录堆栈为空,并且我按下了BackButton应用,即使执行此操作,也会关闭：

private void App_BackRequested(object sender, BackRequestedEventArgs e)
{
        e.Handled = true;
}

我也尝试过

HardwareButtons.BackPressed += App_BackRequested;

这也无济于事.

解决方法:

尝试将以下这些行添加到OnLaunchApplicationAsync方法

protected override Task OnLaunchApplicationAsync(LaunchActivatedEventArgs args)
    {
        //......
        DeviceGestureService.GoBackRequested += (s, e) =>
        {
            e.Handled = true;
            e.Cancel = true;
            if (NavigationService.CanGoBack())
            {
                NavigationService.GoBack();
            }
            else
            {
                // PUT YOUR LOGIC HERE (Confirmation dialog before exit)
                Application.Current.Exit();
            }
        };
        //......
     }