c# - UWP 后台任务在 5 次后未运行

Question

我正在关注 https://learn.microsoft.com/en-us/windows/uwp/launch-resume/create-and-register-a-background-task文档以创建每 15 分钟运行一次并 ping 服务的后台任务。

1. 使用实现 IBackgroundTask 的公共(public)密封类创建 Windows 运行时组件项目

   namespace PeriodicBackgroundTask
   {
       public sealed class FifteenMinutePeriodicTimer : IBackgroundTask
       {
           private static readonly FileLogWriter mWriteLogToFile = new FileLogWriter();
           public FifteenMinutePeriodicTimer() { }
   
           public void Run(IBackgroundTaskInstance taskInstance)
           {
               try
               {
                   taskInstance.Canceled += new BackgroundTaskCanceledEventHandler(OnCanceled);
                   mDeferral = taskInstance.GetDeferral();
                   mWriteLogToFile.log("Starting periodic timer at " + DateTime.Now.ToString());
   
                   // Calling method to do a Post call to a service.
   
                   mWriteLogToFile.log("Finishing periodic timer at " + DateTime.Now.ToString());
               }
               catch (Exception ex)
               {
                   mWriteLogToFile.log("Fifteen Minute periodic timer failed.", ex);
               }
               finally
               {
                   // Adding some buffer for async processes to finish.    
                   Task.Delay(TimeSpan.FromSeconds(15)).Wait();
                   mDeferral.Complete();
               }
           }
   
           private void OnCanceled(IBackgroundTaskInstance sender, BackgroundTaskCancellationReason reason)
           {
               mWriteLogToFile.log("Fifteen minute periodic timer is canceled. {0}", reason.ToString());
           }
       }
   }
   

2. UWP 应用程序的 Package.appmanifest 文件中的条目

   <Extension Category="windows.backgroundTasks" EntryPoint="PeriodicBackgroundTask.FifteenMinutePeriodicTimer">
     <BackgroundTasks>
       <Task Type="systemEvent" />
       <Task Type="timer" />
     </BackgroundTasks>
   </Extension>
   

3. 在App.xaml.cs的OnLaunched方法开头注册定时器

   public async static Task RegisterBackgroundTask()
   {
       foreach (var task in BackgroundTaskRegistration.AllTasks)
       {
           if (String.Equals(task.Value.Name, TASK_NAME))
           {
               mWriteLogToFile.log("Old version of fifteen minute periodic timer found. Unregistering it.");
               BackgroundExecutionManager.RemoveAccess();
               // Unregistering so that any update in Background task can be applied.
               task.Value.Unregister(true);
               break;
           }
       }
       BackgroundAccessStatus backgroundAccessStatus = await BackgroundExecutionManager.RequestAccessAsync();
       if (backgroundAccessStatus == BackgroundAccessStatus.DeniedByUser ||
       backgroundAccessStatus == BackgroundAccessStatus.DeniedBySystemPolicy)
       {
           mWriteLogToFile.log("Fifteen minute periodic timer registration failed, due to Request access status.");
           return;
       }
   
       BackgroundTaskBuilder builder = new BackgroundTaskBuilder();
       builder.Name = TASK_NAME;
       builder.TaskEntryPoint = "PeriodicBackgroundTask.FifteenMinutePeriodicTimer";
       builder.SetTrigger(new TimeTrigger(15, false));
       builder.CancelOnConditionLoss = false;
   
       var backgroundTask = builder.Register();
       if (backgroundTask != null)
       {
           mWriteLogToFile.log("Fifteen minute periodic timer registration SUCCESSFUL.");
       }
       else
       {
           mWriteLogToFile.log("Fifteen minute periodic timer registration FAILED.");
       }
   }
   

安装应用后，FifteenMinuteBackgroundTimer 运行了 5 或 6 次。有时 5，有时 6。当我尝试使用 Visual Studio 调试任务时，我能够调试它。我不确定，为什么 FifteenMinuteBackgroundTimer 在运行 5 次后就死了。谁能告诉我如何调试这个问题？

更多信息:

Windows 版本:1607
Microsoft.NETCore.UniversalWindowsPlatform: 5.1.0

Answer 1

Can anybody please tell me how can I debug this issue?

注册后台任务后，您会发现后台任务显示在生命周期事件工具栏的下拉列表中。在后台任务上设置一个断点，然后点击工具栏中的后台名称，visual studio 将触发后台任务，您可以进行调试。更多详情请引用Debug a background task .

why FifteenMinuteBackgroundTimer is dying after 5 runs.

如果您在后台任务中运行任何异步代码，那么您的后台任务需要使用延迟。看起来您创建了延迟实例，但没有从 IBackgroundTaskInstance 获得延迟。因此，您可能需要先获得延期。

public void Run(IBackgroundTaskInstance taskInstance)
{
    mDeferral = taskInstance.GetDeferral();
    ...
    mDeferral.Complete();       
}

而且您可能不需要 Task.Delay(TimeSpan.FromSeconds(15)).Wait(); 来为异步进程添加一些缓冲区来完成，因为延迟可以帮助您做到这一点。后台任务总共只能运行30s，实际运行时间可能只有25s，如果在后台任务中设置延迟可能会导致无法完成任务而强制关闭。