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
    "
    );



 });



 });

}