CKSubscription object to track changes occurring on the server.
- iOS 8.0+
- macOS 10.10+
- tvOS 9.0+
A subscription acts like a persistent query on the server that can track the creation, deletion, and modification of records. When changes occur, they trigger the delivery of push notifications so that your app can respond appropriately.
Subscription objects do not become active until you save them to the server and the server has time to index them. To save a subscription object, use a
CKModify object or the
save(_: method of
CKDatabase. To cancel a subscription, delete the corresponding subscription object from the server.
Most of the configuration for subscription objects happens at initialization time. The only other piece of configuration to perform is to specify how to deliver push notifications to the user’s device. Use the
notification property of this object to configure the push notification delivery options. You must save the subscription object to the database before your changes take effect.
Handling the Resulting Push Notifications
When a record modification causes a subscription to fire, the server sends push notifications to all devices with that subscription except for the one that made the original change to the record. For subscription-generated push notifications, the server can add data to the notification payload that indicates the condition that triggered the notification. In the
application(_: method of your app delegate, create a
CKNotification object from the the provided
user dictionary. You can query the
CKNotification object for the information relevant to the notification.
In addition to sending a record ID with a push notification, you can ask the server to send a limited amount of data from the record that triggered the notification. In the
CKSubscription object you assign to your subscription’s
notification property, you can use the
desired property to specify one or more keys to include in the notification.
Because push notifications have a limited payload size, the server may omit keys and other pieces of data to keep the payload under the maximum limit. If that happens, you can fetch the entire data payload from the server with a
CKFetch object. That operation object returns instances of the
CKRecord classes that provide information about the push notifications that were delivered to your app.