- (void)applicationDidEnterBackground:(UIApplication *)application

{

    bgTask = [application beginBackgroundTaskWithName:@"MyTask" expirationHandler:^{

        // Clean up any unfinished task business by marking where you

        // stopped or ending the task outright.

        [application endBackgroundTask:bgTask];

        bgTask = UIBackgroundTaskInvalid;

    }];

    // Start the long-running task and return immediately.

    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, ), ^{

        // Do the work associated with the task, preferably in chunks.

        [application endBackgroundTask:bgTask];

        bgTask = UIBackgroundTaskInvalid;

    });

}

Swift

func beginBackgroundTaskWithExpirationHandler(_ handler: (() -> Void)?) -> UIBackgroundTaskIdentifier

Objective-C

- (UIBackgroundTaskIdentifier)beginBackgroundTaskWithExpirationHandler:(void (^)(void))handler

    Listing - Starting a background task at quit time

    - (void)applicationDidEnterBackground:(UIApplication *)application

    {

    UIApplication* app = [UIApplication sharedApplication];

    bgTask = [app beginBackgroundTaskWithExpirationHandler:^{

    [app endBackgroundTask:bgTask];

    bgTask = UIBackgroundTaskInvalid;

    }];

    // Start the long-running task and return immediately.

    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,

    ), ^{

    // Do the work associated with the task.

    [app endBackgroundTask:bgTask];

    bgTask = UIBackgroundTaskInvalid;

    });

    }   

^{} block 语法。

dispatch_queue_create

dispatch_release

dispatch_async_f

Queue: dispatch_queue_t;

Queue := dispatch_queue_create('Video Capture Queue', );