Question

It seems to be customary for apps that are using APN to get the token from the OS whenever the app launches. However if an app has already obtained it once, is there any point in it bothering to obtain it again (and consequently sending it to the server if its already done so).

Can the APN token obtained from the OS ever change?

Answer 1

The answer to your question is inside Apple docs (Local and Push Notification Programming Guide):

By requesting the device token and passing it to the provider every time your application launches, you help to ensure that the provider has the current token for the device. If a user restores a backup to a device or computer other than the one that the backup was created for (for example, the user migrates data to a new device or computer), he or she must launch the application at least once for it to receive notifications again. If the user restores backup data to a new device or computer, or reinstalls the operating system, the device token changes. Moreover, never cache a device token and give that to your provider; always get the token from the system whenever you need it. If your application has previously registered, calling registerForRemoteNotificationTypes: results in the operating system passing the device token to the delegate immediately without incurring additional overhead.