ios 後臺執行程序

- (void)applicationDidEnterBackground:(UIApplication *)application
{
    if ([[UIDevice currentDevice] isMultitaskingSupported]) {
        //Check if device supports mulitasking
        
        UIApplication *application = [UIApplication sharedApplication];
        //Get the shared application instance
        
        __block UIBackgroundTaskIdentifier background_task;
        //Create a task object
        background_task = [application beginBackgroundTaskWithExpirationHandler: ^ {
            [application endBackgroundTask: background_task];
            /** Tell the system that we are done with the tasks **/
            background_task = UIBackgroundTaskInvalid;
            /** Set the task to be invalid **/
            /** System will be shutting down the app at any point in time now **/
        }];
        /** Background tasks require you to use asyncrous tasks **/
        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
            NSLog(@"\n\nRunning in the background!\n\n");
        });
    }
}