Instance Method

application(_:didReceiveRemoteNotification:fetchCompletionHandler:)

Tells the app that a remote notification arrived that indicates there is data to be fetched.

Declaration

optional func application(_ application: UIApplication, didReceiveRemoteNotification userInfo: [AnyHashable : Any], fetchCompletionHandler completionHandler: @escaping (UIBackgroundFetchResult) -> Void)

Parameters

application

Your singleton app object.

userInfo

A dictionary that contains information related to the remote notification, potentially including a badge number for the app icon, an alert sound, an alert message to display to the user, a notification identifier, and custom data. The provider originates it as a JSON-defined dictionary that iOS converts to an NSDictionary object; the dictionary may contain only property-list objects plus NSNull. For more information about the contents of the remote notification dictionary, see Local and Remote Notification Programming Guide.

handler

The block to execute when the download operation is complete. When calling this block, pass in the fetch result value that best describes the results of your download operation. You must call this handler and should do so as soon as possible. For a list of possible values, see the UIBackgroundFetchResult type.

Discussion

Use this method to process incoming remote notifications for your app. Unlike the application(_:didReceiveRemoteNotification:) method, which is called only when your app is running in the foreground, the system calls this method when your app is running in the foreground or background. In addition, if you enabled the remote notifications background mode, the system launches your app (or wakes it from the suspended state) and puts it in the background state when a remote notification arrives. However, the system does not automatically launch your app if the user has force-quit it. In that situation, the user must relaunch your app or restart the device before the system attempts to launch your app automatically again.

When a remote notification arrives, the system displays the notification to the user and launches the app in the background (if needed) so that it can call this method. Launching your app in the background gives you time to process the notification and download any data associated with it, minimizing the amount of time that elapses between the arrival of the notification and displaying that data to the user.

As soon as you finish processing the notification, you must call the block in the handler parameter or your app will be terminated. Your app has up to 30 seconds of wall-clock time to process the notification and call the specified completion handler block. In practice, you should call the handler block as soon as you are done processing the notification. The system tracks the elapsed time, power usage, and data costs for your app’s background downloads. Apps that use significant amounts of power when processing remote notifications may not always be woken up early to process future notifications.