Marks the beginning of a new long-running background task.
- iOS 4.0+
- tvOS 9.0+
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.
A unique identifier for the new background task. You must pass this value to the
end method to mark the end of this task. This method returns
UIBackground if running in the background is not possible.
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
application 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
end 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
background property.) If you do not call
end 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.
To assist with debugging, this method generates a name for the task that is based on the name of the calling method or function. If you want to specify a custom name, use the
begin method instead.