Does the APNS device token ever change, once created?

Once created does the push notification device token ever change?

Example when the app is updated? or in any other case it can change??

Apple's official documentation is unclear on this point. What I have observed is this: the token is invariant for a given device, application, and domain (production vs. sandbox). I believe that this must remain true in order for the system to work reliably. Consider the situation where an application update triggers a new APN token; if I were using the greatest new Twitter-like app, with notifications enabled, what would happen when I update my app from iTunes? Should I have the expectation that it will continue to be sent notifications even though I have not run the applications since I "sync" the update onto me device? The act of changing the application cannot affect the APN system since the OS can receive notifications on your behalf even though you haven't run the updated app.

To be clear, Apple states "An application should register [with APN servers] every time it launches and give its provider the current token". I wholeheartedly agree; doing so will protect your application from bad assumptions or unusual situations.

One of the answers to https://stackoverflow.com/questions/2751481/are-push-notification-tokens-unique-across-all-apps-for-a-single-device indicates that device tokens are unique per "operating system install"; and that restoring from backup to a device would maintain the token but wiping a device will cause it to get a new token. This would be entirely consistent with Apple's intentions of seamless operation and privacy: wiping a device is severe enough that perhaps it warrants a new association, but a user restoring an image after an OS update would want to preserve their existing notifications. If I recall the recent iOS5 update on my iPad, I restored the most recent backup after upgrading, so this would have maintained my notification token's consistency. [Edit: restoring a backup to a different device will NOT duplicate the token.]

caveat: I do not have definitive knowledge on the subject, just some reasonable experience working with APN (as a third-party developer). As always, it is best to verify your assumptions.

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Update (June 2012):

I recently had a chance to a> talk to Apple engineers and b> run some real world tests, and I wanted to present the results:

To be complete, when I talk about returning an APN token, I am assuming the context of a single bundle identifier/application.

First, the Apple engineers said that it should not be possible for two devices to return the same APN. Notwithstanding the comments below, I have not been able to identify a circumstance where this fails.

Second, here is the upgrade test sequence and results:

1. Start with iOS4 installed on iPhone4; backup device in iTunes

2. Upgrade to iOS5
   From a previous test, I know that the APN token is now different

3. Restore the backup to the device
   The APN token is now the same as step 1.

4. Reset iOS (clean device)
   The APN Token changes

5. Backup a different phone to iTunes and restore that backup to test device; basically, I'm restoring the "wrong" backup, as if I were switching phones.
   The APN token changes again; further it is distinct and does not match the tokens either the original token or the "cloned" token.

6. Restore the "correct" backup to the device.
   The APN token is now the same as step 1.

7. Lastly, I upgraded the phone to iOS6 (beta2), restored my backup, and re-tested. As expected, the token continued to match the token in step 1.

At this point, I'm pretty confident that APN tokens can't be duplicated between different devices; perhaps this may have happened as a bug in earlier versions of iOS, but I'm confident that iOS5 (and presumably iOS6) are handling APN tokens correctly.

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Update (August 2012)

I just realized I had not added this: device tokens will change. One of the Apple devs shared with me that tokens do actually expire (after 2 years, I think). For many purposes, this is long enough that can be thought of as invariant.

[I'm not worried if I have to update my test scripts with new tokens every two years, especially since I change phones every year.]

From [Apple Documentation ApplePushService]2

> 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.

I've just tested it with iOS9 and APN Push token changes if I reinstall an app.

YES, device tokens can change.

Anytime your app receives a token, it should store it. Then, whenever a new token is received (which will happen, eventually), compare the new token to the stored token and, if they are different:

1. Update the device's local storage, (including possibly to nil)
2. Update anything on the device which uses the token to be aware of the new token
3. Update any APIs which are aware of this token to the new token.

As a practical matter, the last step is the most likely to be non-trivial. For example, if you have a service which is sending weather alerts to a device token based on what zip code that device has subscribed to, then you need to pass the old_token and the new_token to said service so it can update delivery.

Ergo, generally speaking 100% of APIs accepting a "device token" must also have some kind of UPDATE facility for that token. To not build for this is to build for mis-delivered and non-delivered notifications.

Device token does change from iOS 8 and later

Please see text below from Apple website. Registering, Scheduling, and Handling User Notifications > The device token is your key to sending push notifications to your app on a specific device. Device tokens can change, so your app needs to reregister every time it is launched and pass the received token back to your server. If you fail to update the device token, remote notifications might not make their way to the user’s device. Device tokens always change when the user restores backup data to a new device or computer or reinstalls the operating system. When migrating data to a new device or computer, the user must launch your app once before remote notifications can be delivered to that device.

I think it is worth mentioning as nobody did it that the token changes after you have called unregisterForRemoteNotifications. When you call registerForRemoteNotifications next time the token is different. I failed to find any confirmation of this in the Apple docs but I witnessed such a behavior myself. Please keep this in mind

It shouldn't change, unless your app is restored onto a new device (at which point it won't be asked to accept push notifications again, and will simply send you the registered call at which point you should accept the new token).

But Apple doesn't guarantee that it never changes (hence the documentation never mentions it). You better program for the worst and assume it may change one day. Also, sending a token to your server regularly enables you to remove tokens that haven't registered for a while, and have probably deinstalled your app or lost interest a while ago (and the documentation does specify this as wanted behavior!).

Links quickly become obsolete with apple! so i'm quoting what seems to be quite clear now :

> Never cache device tokens in your app; instead, get them from the system when you need them. APNs issues a new device token to your app when certain events happen. The device token is guaranteed to be different, for example, when a user restores a device from a backup, when the user installs your app on a new device, and when the user reinstalls the operating system. Fetching the token, rather than relying on a cache, ensures that you have the current device token needed for your provider to communicate with APNs. When you attempt to fetch a device token but it has not changed, the fetch method returns quickly.

From this guide

From - Apple Docs

> APNs can issue a new device token for a variety of reasons: > > - User installs your app on a new device >
> - User restores device from a backup >
> - User reinstalls the operating system >
> - Other system-defined events > > As a result, apps must request the device token at launch time.

Additionally:

> _{I M P O R T A N T} > > APNs device tokens are of variable length. Do not hard-code their > size.

As reference to Apple push notification stuff

The device token is your key to sending push notifications to your app on a specific device. Device tokens can change, so your app needs to reregister every time it is launched and pass the received token back to your server. If you fail to update the device token, remote notifications might not make their way to the user’s device. Device tokens always change when the user restores backup data to a new device or computer or reinstalls the operating system. When migrating data to a new device or computer, the user must launch your app once before remote notifications can be delivered to that device.

Never cache a device token; always get the token from the system whenever you need it. If your app previously registered for remote notifications, calling the registerForRemoteNotifications method again does not incur any additional overhead, and iOS returns the existing device token to your app delegate immediately. In addition, iOS calls your delegate method any time the device token changes, not just in response to your app registering or re-registering.

According to this link the device token

> The device token included in each request represents the identity of > the device receiving the notification. APNs uses device tokens to > identify each unique app and device combination. It also uses them to > authenticate the routing of remote notifications sent to a device. > Each time your app runs on a device, it fetches this token from APNs > and forwards it to your provider. Your provider stores the token and > uses it when sending notifications to that particular app and device. > The token itself is opaque and persistent, changing only when a > device’s data and settings are erased. Only APNs can decode and read a > device token.

Yes it can change. Ideally when ever we receive a token via the callback method

> - (void)application:(UIApplication *)application didRegisterForRemoteNotificationsWithDeviceToken:(NSData *)deviceToken

The app should register / refresh the token on the remote server. This will ensure that the token on the APNS and your server is kept in sync.

As per Apple documentation,

> Obtaining and handling an app-specific device token works as follows: > > Your app registers with APNs for remote notifications When a new > device token is needed, APNs generates one using information contained > in the device’s certificate. It encrypts the token using a token key > and returns it to the device, as shown in the middle, right-pointing > arrow. The system delivers the device token back to your app by > calling your > application:didRegisterForRemoteNotificationsWithDeviceToken: delegate > method. Upon receiving the token, your app (within the delegate > method) must forward it to your provider in either binary or > hexadecimal format. Your provider cannot send notifications to the > device without this token. For details, see Registering to Receive > Remote Notifications in Configuring Remote Notification Support.

The device token relay on the installation of the app.

It means that if you reinstall the application, it changes; it doesn't metter if you do it from a backup, an iOS upgrade ecc..

The right way to use it, to avoid any problem, is to get the one given on the NSPAppDelegate at each application launch, in the method didRegisterForRemoteNotificationsWithDeviceToken