Windows Phone 8 push notification push channel always creates new channel uri

Question

I wanted to check that my push notification implementation is correct.

Each time I open my app (in actual fact I register the push channel only on a specific page so it's each time I go back and forth from that page) a new push channel URI is created which I store in my mobile services database to send push notifications to. This doesn't seem correct to me as each time the app/page is opened a new push channel URI is generated and so the list of channel URIs just grows and grows for each device that uses my app. I'd assume that you create a push channel, store the channel URI and push to it as needed. I will make note here that I am using raw push notifications.

I understand that push channels will expire every so often but for me it's occurring each time I back out of the app/page and therefore when onNavigateTo is called I find the push channel which does exist and a new channel URI is always created. Is this correct?

My code is as follows:

protected override void OnNavigatedTo(NavigationEventArgs e) { registerPushChannel(); }

private void registerPushChannel()
    {
        // The name of our push channel.
        string channelName = "RawSampleChannel";

        // 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);

            // 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);
            pushChannel.HttpNotificationReceived += new EventHandler<HttpNotificationEventArgs>(PushChannel_HttpNotificationReceived);

            pushChannel.Open();

        }
        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);
            pushChannel.HttpNotificationReceived += new EventHandler<HttpNotificationEventArgs>(PushChannel_HttpNotificationReceived);

            // code which passes the new channel URI back to my web service               

        }

    }

protected override void OnNavigatedFrom(NavigationEventArgs e)
    {
        pushChannel.Close();
    }

So to clarify, the app is opened and the push channel is registered and the channel uri is saved in my web service. The web service then sends notifications to the channel uri. When I exit the app or page and return to it, the push channel is found but a new channel uri is created which I again save to my web service. My channels table in effect just keeps growing and growing.

So is this the way it should work with new channel URIs continually generated? It kind of doesn't make sense to me. I'm not sure how toast and tile notifications work but I'd assume the channel URI needs to be static when the app closes to keep receiving notifications while the app is closed, but perhaps that could be a functionality of bindtotoast and bindtotile and so what I'm doing is correct because it's to do with raw notifications.

Matti

I'm struggling with what I actually put in 'PushChannel_ChannelUriUpdated'. Could you give an example? – Laudation

Answer 1

You're mostly doing it right.

Push Notifications are a funny thing.
You create a channel, send it to your server and then the server can send until it fails (the channel Uri expires or there's an error). At which point the app needs to create a new ChannelUri and then UPDATE the value stored for that app/device on the server. The server will then be able to send notifications.

Some important points

1. When a new channel Uri is requested for one that is still valid you'll get the same one back.
2. When your ask for a new channel uri and the current one has expired, you'll normally get the same uri returned but the channel will be made live again.
3. There is no way to know if a channel has expired from within an app without running code like your registerPushChannel method. (Unless you track this on your backend and the app queries the backend.)
4. There is no way to tell the app that a channel has expired, or tell the user to reopen the app to re-establish a channel connection using the push infrastructure.

The standard way to try and ensure that the channel is always available is to check the channel whenever the app is started.
This is what you're doing, you probably just want to make sure you're updating server records not just adding more.

Mauney

Sweet. Thanks for that. Yep on insert I check that the channel Uri for that user doesn't already exist. Good to know I'm doing it right. Thanks again. – Matti