Question

I red the method - (void)application:(UIApplication *)application didRegisterForRemoteNotificationsWithDeviceToken:(NSData *)deviceToken is sent to the delegate when the application successfully registers with Apple Push Service (APS). At a low level how does this work? Does the application try to call it anytime you start an app AND verifies the device is connected? Is it called multiple times until the device is connected? Does it stop working when you have received your device token?

Thanks in advance.

Answer 1

The didRegister callback is actually a direct response to the - (void)registerForRemoteNotificationTypes:(UIRemoteNotificationType)types method. Every time your application starts up, it’s your responsibility to:

1. Call registerForRemoteNotificationTypes: on your application object (UIApplication / NSApplication)
2. Respond to application:didRegisterForRemoteNotificationsWithDeviceToken and the application:didFailToRegisterForRemoteNotificationsWithError: callbacks.
3. Send the device token to whatever service you’re communicating with so that it may use that device token in the future.

To specifically answer your questions:

1. You’ll get ‘didFailToRegister’ if the network is unreachable or if you haven’t properly signed your application. The NSError that comes back is fairly descriptive.
2. Once the application has started and you have successfully registered for remote notifications, you do not need to register again. There’s no harm in doing it, but there’s really no point. If you’ve failed, you can try to register again at a later date (i.e. when the APNS is reachable again).
3. You will only get one callback (either success or failure)