push-notification - signal - send notification

La propiedad de desencadenante Registro de base es nula

Question

Hola quiero recibir notificaciones push en la tarea de fondo para la biblioteca portátil que he creado aquí esta es mi clase de tarea de fondo

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Xml.Linq;
using Windows.ApplicationModel.Background;
using Windows.Data.Xml.Dom;
using Windows.Networking.PushNotifications;
using Windows.Storage;
using Windows.UI.Notifications;

namespace BackgroundTask
{
    public sealed class NotificationTask : IBackgroundTask
    {
        public void Run(IBackgroundTaskInstance taskInstance)
        {

            // Get the background task details
            ApplicationDataContainer settings = ApplicationData.Current.LocalSettings;
            string taskName = taskInstance.Task.Name;

            Debug.WriteLine("Background " + taskName + " starting...");

            // Store the content received from the notification so it can be retrieved from the UI.
            ToastNotification notification = (ToastNotification )taskInstance.TriggerDetails;
            settings.Values[taskName] = notification.Content;
            NotificationTask.AddTostNotification(notification.Content);

            Debug.WriteLine("Background " + taskName + " completed!");
        }



    private static void AddTostNotification(String xmlDocument)
    {

        List<string> messageSection = NotificationTask.GetMessageAndLandingPage(xmlDocument, "toast");

        if (messageSection == null) { return; }

        ToastTemplateType toastTemplate = ToastTemplateType.ToastText01;

        XmlDocument toastXml = ToastNotificationManager.GetTemplateContent(toastTemplate);
        XmlNodeList toastTextElements = toastXml.GetElementsByTagName("text");
        toastTextElements[0].AppendChild(toastXml.CreateTextNode(messageSection[0]));
        //  toastTextElements[1].AppendChild(toastXml.CreateTextNode(message));

        IXmlNode toastNode = toastXml.SelectSingleNode("/toast");
        ((XmlElement)toastNode).SetAttribute("launch", messageSection[1]);

        XmlElement audio = toastXml.CreateElement("audio");
        audio.SetAttribute("src", "ms-appx:///Assets/Play-Guitar.wav");
        //audio.SetAttribute("loop", "true");
        toastNode.AppendChild(audio);

        //launch tost immediatly
        ToastNotification toast = new ToastNotification(toastXml);
        ToastNotificationManager.CreateToastNotifier().Show(toast);

    }

Aquí estoy registrando la tarea

    internal async void InitChannel()
    {

        // Applications must have lock screen privileges in order to receive raw notifications
        BackgroundAccessStatus backgroundStatus = await BackgroundExecutionManager.RequestAccessAsync();

        // Make sure the user allowed privileges
        if (backgroundStatus != BackgroundAccessStatus.Denied && backgroundStatus != BackgroundAccessStatus.Unspecified)
        {
            Windows.Storage.ApplicationDataContainer roamingSettings = Windows.Storage.ApplicationData.Current.LocalSettings;

            try
            {
                var channel = await PushNotificationChannelManager.CreatePushNotificationChannelForApplicationAsync();

                if (channel != null)
                {

                    roamingSettings.Values["ExistingPushChannel"] = channel.Uri;

                    dispatcher = Windows.UI.Core.CoreWindow.GetForCurrentThread().Dispatcher;
                    channel.PushNotificationReceived += OnPushNotificationReceived;

                    UnregisterBackgroundTask();
                    RegisterBackgroundTask();

                }
                else
                {
                    roamingSettings.Values["ExistingPushChannel"] = "Failed to create channel";
                }
            }
            catch
            {
                roamingSettings.Values["ExistingPushChannel"] = "Failed to create channel";
            }
        }

    }
   private void RegisterBackgroundTask()
    {
        BackgroundTaskBuilder taskBuilder = new BackgroundTaskBuilder();
        PushNotificationTrigger trigger = new PushNotificationTrigger();

        taskBuilder.SetTrigger(trigger);

        // Background tasks must live in separate DLL, and be included in the package manifest
        // Also, make sure that your main application project includes a reference to this DLL

        taskBuilder.TaskEntryPoint = "BackgroundTask.NotificationTask";
        taskBuilder.Name = "PlaypushNotification";

        try
        {
            BackgroundTaskRegistration task = taskBuilder.Register();
            task.Completed += BackgroundTaskCompleted;
        }
        catch 
        {             
            UnregisterBackgroundTask();
        }
    }

    private bool UnregisterBackgroundTask()
    {
        foreach (var iter in BackgroundTaskRegistration.AllTasks)
        {
            IBackgroundTaskRegistration task = iter.Value;
            if (task.Name == "PlaypushNotification")
            {
                task.Unregister(true);
                return true;
            }
        }
        return false;
    }

En mi archivo Manifest

  <Extensions>
    <Extension Category="windows.backgroundTasks" EntryPoint="BackgroundTask.NotificationTask">
      <BackgroundTasks>
        <Task Type="pushNotification" />
      </BackgroundTasks>
    </Extension>
  </Extensions>

El disparador de PushNotification no se activa, cuando depuro encontré que la propiedad del disparador de BackgroundTaskRegistration es nula. ¿cual es el problema? ¿Qué mal está yendo aquí?