Should we register for iOS push notification every time during application launch?

Question

We are using remote notifications in our iOS application and we are registering to APNS server inside application: didFinishLaunching: delegate method. That means it will be registered with APNS server every time the application launched freshly. Below is the code snippet.

[[UIApplication sharedApplication] registerForRemoteNotifications]

We have noticed that the device token (which is delivered to us by APNS server) is same every time. So, we thought that we can save the token in NSUserDefaults and use it later. In application: didFinishLaunching: method, we can give a check if the device token is present in NSUserDefaults or not. If it's available, we can use the same instead of registering to APNS. Otherwise, we can opt to register with APNS.

But, from the Apple documentation, it's observed that "they encourage us to register for remote notifications each time the application is launched freshly". Below is the screenshot from docs.

When does the device token value change actually? Can I afford to store the device token in NSUserDefaults and use it later instead of registering every time? Please help!! Thanks in advance!!

Answer 1

To answer your question with some apple documentation:

The form of this phase of token trust ensures that only APNs generates the token which it will later honor, and it can assure itself that a token handed to it by a device is the same token that it previously provisioned for that particular device—and only for that device.

If the user restores backup data to a new device or reinstalls the operating system, the device token changes.

This means you shouldn't really store the token in your NSUserDefaults.

However if you want to save it anyway I recommend to save it in the Keychain. See this example how to do so: Store Device Token in Keychain

Another quote from apple documentation:

"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 other than the one that the backup was created for (for example, the user migrates data to a new device), 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 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 iOS passing the device token to the delegate immediately without incurring additional overhead."

EDIT: Looks like the above links to Apple's documentation are broken by now. Here is a updated link (thanks to @Enrico Cupellini): https://developer.apple.com/library/content/technotes/tn2265/_index.html