c# - UWP OnBackgroundActivated，找不到合适的方法来覆盖

Question

我正在尝试使用新的“单进程模型后台事件”API 来支持我的应用程序的后台任务。但是，我得到的是，在“OnBackgroundActivated”方法上“找不到合适的方法来覆盖”。我的代码有什么问题？

public MainPage()
    {
        this.InitializeComponent();
        Application.Current.EnteredBackground += Current_EnteredBackground;
    }

    private async void Current_EnteredBackground(object sender, Windows.ApplicationModel.EnteredBackgroundEventArgs e)
    {
        await RegisterBackgroundTask();
    }

    protected override void OnBackgroundActivated(BackgroundActivatedEventArgs args)
    {
        // show a toast
    }

    private void Page_Loaded(object sender, RoutedEventArgs e)
    {

    }

    private async Task RegisterBackgroundTask()
    {
        BackgroundAccessStatus backgroundAccessStatus = await BackgroundExecutionManager.RequestAccessAsync();

        if (backgroundAccessStatus == BackgroundAccessStatus.AllowedSubjectToSystemPolicy ||
            backgroundAccessStatus == BackgroundAccessStatus.AlwaysAllowed)
        {
            foreach (var bgTask in BackgroundTaskRegistration.AllTasks)
            {
                if (bgTask.Value.Name == "MyTask")
                {
                    bgTask.Value.Unregister(true);
                }
            }

            var builder = new BackgroundTaskBuilder();
            builder.Name = "MyTask";
            builder.SetTrigger(new TimeTrigger(15, false));

            // use builder.TaskEntryPoint if you want to not use the default OnBackgroundActivated
            // we’ll register it and now will start work based on the trigger, here we used a Time Trigger
            BackgroundTaskRegistration task = builder.Register();
        }
    }

Answer 1

这里的问题是您试图覆盖 MainPage 类中的 OnBackgroundActivated 方法。 MainPage 类派生自 Page Class , 但是 Application.OnBackgroundActivated method是 Application class 的一种方法这在 Page 类中不存在，因此您得到了 找不到合适的方法来覆盖 错误。

要解决此问题，我们需要将 OnBackgroundActivated 方法放在 App 类中，例如:

sealed partial class App : Application
{
    /// <summary>
    /// Override the Application.OnBackgroundActivated method to handle background activation in 
    /// the main process. This entry point is used when BackgroundTaskBuilder.TaskEntryPoint is 
    /// not set during background task registration.
    /// </summary>
    /// <param name="args"></param>
    protected override void OnBackgroundActivated(BackgroundActivatedEventArgs args)
    {
        //TODO
    }
}

关于单进程后台任务的更多信息，请参见Support your app with background tasks和 Background activity with the Single Process Model .