Instance Method

beginBackgroundTask(withName:expirationHandler:)

Marks the beginning of a new long-running background task with the specified name.

Declaration

func beginBackgroundTask(withName taskName: String?, expirationHandler handler: (() -> Void)? = nil) -> UIBackgroundTaskIdentifier

Parameters

taskName

The name to display in the debugger when viewing the background task. If you specify nil for this parameter, this method generates a name based on the name of the calling function or method.

handler

A handler to be called shortly before the app’s remaining background time reaches 0. Use this handler to clean up and mark the end of the background task. Failure to end the task explicitly will result in the termination of the app. The system calls the handler synchronously on the main thread, blocking the app’s suspension momentarily.

Return Value

A unique identifier for the new background task. You must pass this value to the endBackgroundTask(_:) method to mark the end of this task. This method returns invalid if running in the background is not possible.

Discussion

This method requests additional background execution time for your app. Call this method when leaving a task unfinished might be detrimental to your app’s user experience. For example, call this method before writing data to a file to prevent the system from suspending your app while the operation is in progress. Do not use this method simply to keep your app running after it moves to the background.

Call this method as early as possible before starting your task, and preferably before your app actually enters the background. The method requests the task assertion for your app asynchronously. If you call this method shortly before your app is due to be suspended, there is a chance that the system might suspend your app before that task assertion is granted. For example, do not call this method at the end of your applicationDidEnterBackground(_:) method and expect your app to continue running. If the system is unable to grant the task assertion, it calls your expiration handler.

Each call to this method must be balanced by a matching call to the endBackgroundTask(_:) method. Apps running background tasks have a finite amount of time in which to run them. (You can find out how much time is available using the backgroundTimeRemaining property.) If you do not call endBackgroundTask(_:) for each task before time expires, the system kills the app. If you provide a block object in the handler parameter, the system calls your handler before time expires to give you a chance to end the task.

You can call this method at any point in your app’s execution. You may also call this method multiple times to mark the beginning of several background tasks that run in parallel. However, each task must be ended separately. You identify a given task using the value returned by this method.

This method can be safely called on a non-main thread. To extend the execution time of an app extension, use the performExpiringActivity(withReason:using:) method of ProcessInfo instead.

Use BGProcessingTask for discretionary background processing tasks that require longer periods of time.

See Also

Managing Background Execution

var backgroundRefreshStatus: UIBackgroundRefreshStatus

Indicates whether the app can refresh content when running in the background.

enum UIBackgroundRefreshStatus

Constants indicating whether background execution is enabled for the app.

class let backgroundRefreshStatusDidChangeNotification: NSNotification.Name

Posted when the app’s status for downloading content in the background changes.

func endBackgroundTask(UIBackgroundTaskIdentifier)

Marks the end of a specific long-running background task.

struct UIBackgroundTaskIdentifier

A unique token that identifies a request to run in the background.

var backgroundTimeRemaining: TimeInterval

The amount of time the app has to run in the background.