Instance Method

application(_:performFetchWithCompletionHandler:)

Tells the app that it can begin a fetch operation if it has data to download.

Declaration

optional func application(_ application: UIApplication, performFetchWithCompletionHandler completionHandler: @escaping (UIBackgroundFetchResult) -> Void)

Parameters

application

Your singleton app object.

completionHandler

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

Implement this method if your app supports the fetch background mode. When an opportunity arises to download data, the system calls this method to give your app a chance to download any data it needs. Your implementation of this method should download the data, prepare that data for use, and call the block in the completionHandler parameter.

When this method is called, your app has up to 30 seconds of wall-clock time to perform the download operation and call the specified completion handler block. In practice, your app should call the completion handler block as soon as possible after downloading the needed data. If you do not call the completion handler in time, your app is terminated. More importantly, the system uses the elapsed time to calculate power usage and data costs for your app’s background downloads. If your app takes a long time to call the completion handler, it may be given fewer future opportunities to fetch data in the future. For more information about supporting background fetch operations, see Background Execution in App Programming Guide for iOS.

See Also

Downloading Data in the Background

func application(UIApplication, handleEventsForBackgroundURLSession: String, completionHandler: () -> Void)

Tells the delegate that events related to a URL session are waiting to be processed.