When using Google push notifications, I am allowed to specify a collapse_key value so a device will not receive multiple notifications of the same collapse_key.
Does APNS have a similar feature or does anyone know a way to emulate this functionality?
As of iOS 10 and using the HTTP/2.0 APNS API, you can specify apns-collapse-id header and handle the collapse logic in your app.
Collapsed notifications will appear as one single notification on the device that keeps updating with new data. Each time a notification is updated it is pushed to the top of your unread notifications.
Description of apns-collapse-id taken from https://developer.apple.com/library/content/documentation/NetworkingInternet/Conceptual/RemoteNotificationsPG/CommunicatingwithAPNs.html:
Multiple notifications with same collapse identifier are displayed to the user as a single notification. The value should not exceed 64 bytes. For more information, see Quality of Service, Store-and-Forward, and Coalesced Notifications.
When a device is online, all the notifications you send are delivered and available to the user. However, you can avoid showing duplicate notifications by employing a collapse identifier across multiple, identical notifications. The APNs request header key for the collapse identifier is apns-collapse-id and is defined in Table 6-2.
For example, a news service that sends the same headline twice in a row could employ the same collapse identifier for both push notification requests. APNs would then take care of coalescing these requests into a single notification for delivery to a device.