'System.NullReferenceException' Occur when generating a channel URI In Windows Phone

Question

I am working with a windows phone app and I don't know why but I am not getting channel URI for the HttpNotification channel.

I am getting "System.NullReferenceException". My code is working in previous day but same code is not working today.

my C# code is:

    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()));

    }

And I am getting this type of exception

I dont know what actually problem is? This is server problem or anything else?

Answer 1

From my experience, check your notification channel bound status before exit app. If it isn't bound to both tile and toast, Microsoft Push Notification Service will make its subscription invalid and you will get a null channelUrl next time you open app.