UWP进程内AppService如何仅在宿主应用运行时接受连接？

更新内容 #

OnLaunched(LaunchActivatedEventArgs e)方法是否仅在用户手动启动应用的常规启动场景下触发？若如此，我打算通过布尔变量AppIsRunning跟踪应用运行状态，代码如下：

private static bool AppIsRunning = false;

protected override async void OnLaunched(LaunchActivatedEventArgs e)
{
    ...    
    AppIsRunning = true;
    ...
}

private AppServiceConnection AppServiceConnection;
private BackgroundTaskDeferral AppServiceDeferral;

protected override void OnBackgroundActivated(BackgroundActivatedEventArgs args)
{
    base.OnBackgroundActivated(args);

    IBackgroundTaskInstance taskInstance = args.TaskInstance;
    AppServiceTriggerDetails appService = taskInstance.TriggerDetails as AppServiceTriggerDetails;
    AppServiceDeferral = taskInstance.GetDeferral();
    taskInstance.Canceled += OnAppServicesCanceled;
    AppServiceConnection = appService.AppServiceConnection;
    AppServiceConnection.RequestReceived += OnAppServiceRequestReceived;
    AppServiceConnection.ServiceClosed += AppServiceConnection_ServiceClosed;
}
private async void OnAppServiceRequestReceived(AppServiceConnection sender, AppServiceRequestReceivedEventArgs args)
{
    if (AppIsRunning)
    {
        AppServiceDeferral messageDeferral = args.GetDeferral();
        ValueSet response = (await IPC.Controller.ProcessIncomeRequests(args.Request.Message.ToDictionary())).ToValueSet();
        await args.Request.SendResponseAsync(response);
        messageDeferral.Complete();
    }
}

private void OnAppServicesCanceled(IBackgroundTaskInstance sender, BackgroundTaskCancellationReason reason)
{
    AppServiceDeferral.Complete();
}
private void AppServiceConnection_ServiceClosed(AppServiceConnection sender, AppServiceClosedEventArgs args)
{
    AppServiceDeferral.Complete();
}

请问该方案是否可行？

核心结论 #

你的思路可行，但需要补充状态维护的逻辑，确保AppIsRunning能准确反映应用的活跃状态，同时可以优化连接拦截的时机。

细节补充与优化 #

1. OnLaunched的触发场景
   OnLaunched并非只在用户手动启动时触发，应用从挂起状态恢复、通过协议激活等场景也会触发它，但如果应用是被AppService后台激活，OnLaunched不会执行——这刚好符合你的需求：此时AppIsRunning保持false，会自动拒绝连接。

2. 完善状态切换逻辑
   当前代码只在OnLaunched中设置AppIsRunning = true，但没有处理应用进入后台/挂起的情况。当用户切换应用到后台，系统可能会挂起应用，此时需要把AppIsRunning设为false，避免出现应用已挂起但仍被标记为运行的错误：

   protected override void OnEnteredBackground(EnteredBackgroundEventArgs args)
   {
       base.OnEnteredBackground(args);
       AppIsRunning = false;
   }
   
   protected override void OnLeavingBackground(LeavingBackgroundEventArgs args)
   {
       base.OnLeavingBackground(args);
       AppIsRunning = true;
   }
   

3. 提前拦截非活跃状态的连接
   你当前的代码是在请求进来时才判断是否处理，其实可以在OnBackgroundActivated阶段就直接拒绝连接，减少不必要的资源占用：

   protected override void OnBackgroundActivated(BackgroundActivatedEventArgs args)
   {
       base.OnBackgroundActivated(args);
   
       IBackgroundTaskInstance taskInstance = args.TaskInstance;
       AppServiceTriggerDetails appService = taskInstance.TriggerDetails as AppServiceTriggerDetails;
       
       // 应用未运行时直接结束任务，不建立连接
       if (!AppIsRunning)
       {
           var deferral = taskInstance.GetDeferral();
           deferral.Complete();
           return;
       }
   
       AppServiceDeferral = taskInstance.GetDeferral();
       taskInstance.Canceled += OnAppServicesCanceled;
       AppServiceConnection = appService.AppServiceConnection;
       AppServiceConnection.RequestReceived += OnAppServiceRequestReceived;
       AppServiceConnection.ServiceClosed += AppServiceConnection_ServiceClosed;
   }
   

4. 请求处理的容错
   即使在OnAppServiceRequestReceived中判断，也建议给客户端返回明确的拒绝响应，而不是静默忽略，这样客户端可以及时处理连接失败的情况：

   private async void OnAppServiceRequestReceived(AppServiceConnection sender, AppServiceRequestReceivedEventArgs args)
   {
       var messageDeferral = args.GetDeferral();
       if (AppIsRunning)
       {
           ValueSet response = (await IPC.Controller.ProcessIncomeRequests(args.Request.Message.ToDictionary())).ToValueSet();
           await args.Request.SendResponseAsync(response);
       }
       else
       {
           // 返回明确的拒绝响应
           await args.Request.SendResponseAsync(new ValueSet { { "Status", "Error" }, { "Message", "Host app is not running" } });
       }
       messageDeferral.Complete();
   }
   

内容的提问来源于stack exchange，提问作者Miguel