iphone后台功能执行

- (void)applicationDidEnterBackground:(UIApplication *)application {



    __block    UIBackgroundTaskIdentifier bgTask;



    bgTask = [application beginBackgroundTaskWithExpirationHandler:^{



        dispatch_async(dispatch_get_main_queue(), ^{



            if (bgTask != UIBackgroundTaskInvalid)



            {

                bgTask = UIBackgroundTaskInvalid;

            }

        });

    }];



    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{



        dispatch_async(dispatch_get_main_queue(), ^{

            NSLog(@"555555");



        });



    });

}