CKQueryNotification
A notification that triggers when a record that matches the subscription’s predicate changes.
Declaration
class CKQueryNotificationOverview
Query subscriptions execute when a record that matches the subscription’s predicate changes, for example, when the user modifies a field’s value in the record. When CloudKit registers the change, it sends push notifications to the user’s devices to inform your app about the change. You can then fetch the changes and cache them on-device. When appropriate, CloudKit excludes the device where the change originates.
You configure a subscription’s notifications by setting it’s notificationInfo property. Do this before you save it to the server. A subscription generates either high-priority or medium-priority push notifications. CloudKit delivers medium-priority notifications to your app in the background. High-priority notifications are visual and the system displays them to the user. Visual notifications need the user’s permission. For more information, see Asking permission to use notifications.
A subscription uses CKSubscription.NotificationInfo to configure its notifications. For background delivery, set only its shouldSendContentAvailable property to true. If you set any other property, CloudKit treats the notification as high-priority.
Don’t rely on push notifications for changes because the system can coalesce them. CloudKit can omit data to keep the notification’s payload size under the APNs size limit. If you use desiredKeys to include extra data in the payload, the server removes that first. A notification’s isPruned property is true if CloudKit omits data.
Consider notifications an indication of remote changes. Use databaseScope to determine which database contains the changed record. To fetch the changes, configure an instance of CKQueryOperation to match the subscription and then execute it in the database. CloudKit returns all records that match the predicate, including the changed record. Dispose of any records you cache on-device and use the operation’s results instead.
You don’t instantiate this class. Instead, implement application(_:didReceiveRemoteNotification:fetchCompletionHandler:) in your app delegate. Initialize CKNotification with the userInfo dictionary that CloudKit passes to the method. This returns an instance of the appropriate subclass. Use the notificationType property to determine the type. Then cast to that type to access type-specific properties and methods.