'System.NullReferenceException'在生成通道URI時發生在Windows Phone中

Question

我正在使用Windows Phone應用程序，但我不知道爲什麼，但我沒有獲取HttpNotification通道的通道URI。

我得到「System.NullReferenceException」。我的代碼在前一天工作，但相同的代碼今天不工作。

我的C＃代碼：

HttpNotificationChannel pushChannel;   
    string channelName = "ToastSampleChannel"; 

    // Try to find the push channel. 
    pushChannel = HttpNotificationChannel.Find(channelName); 

    // If the channel was not found, then create a new connection to the push service. 
    if (pushChannel == null) 
    { 
     pushChannel = new HttpNotificationChannel(channelName, "www.contoso.com"); 

     // Register for all the events before attempting to open the channel. 
     pushChannel.ChannelUriUpdated += new EventHandler<NotificationChannelUriEventArgs>(PushChannel_ChannelUriUpdated); 
     pushChannel.ErrorOccurred += new EventHandler<NotificationChannelErrorEventArgs>(PushChannel_ErrorOccurred); 

     // Register for this notification only if you need to receive the notifications while your application is running. 
     pushChannel.ShellToastNotificationReceived += new EventHandler<NotificationEventArgs>(PushChannel_ShellToastNotificationReceived); 

     pushChannel.Open(); 

     // Bind this new channel for toast events. 
     pushChannel.BindToShellToast(); 

    } 
    else 
    { 
     // The channel was already open, so just register for all the events. 
     pushChannel.ChannelUriUpdated += new EventHandler<NotificationChannelUriEventArgs>(PushChannel_ChannelUriUpdated); 
     pushChannel.ErrorOccurred += new EventHandler<NotificationChannelErrorEventArgs>(PushChannel_ErrorOccurred); 

     // Register for this notification only if you need to receive the notifications while your application is running. 
     pushChannel.ShellToastNotificationReceived += new EventHandler<NotificationEventArgs>(PushChannel_ShellToastNotificationReceived); 

     // Display the URI for testing purposes. Normally, the URI would be passed back to your web service at this point. 
     System.Diagnostics.Debug.WriteLine(pushChannel.ChannelUri.ToString()); 
     MessageBox.Show(String.Format("Channel Uri is {0}", 
      pushChannel.ChannelUri.ToString())); 

    } 

而且我得到這種類型的異常

我不知道真正的問題是什麼？ 這是服務器問題還是其他問題？

Answer 1

根據我的經驗，在退出應用程序之前檢查您的通知通道綁定狀態。如果未綁定到平鋪和烤麪包，Microsoft推送通知服務將使其訂閱無效，並且您下次打開應用時將獲得空的channelUrl。