1 - (void)applicationDidEnterBackgtound 2 { 3     UIApplication *app = [UIApplication sharedApplication]; 4     __block UIBackgroundTaskIdentifier taskId; 5      6     taskId = [app beginBackgroundTaskWithExpirationHandler:^{ 7         NSLog(@"%@",NSStringFromSelector(_cmd)); 8         [app endBackgroundTask:taskId]; 9     }];10     11     if (taskId == UIBackgroundTaskInvalid) {12         return;13     }14     15     dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{16         //做一些额外的操作17         [app endBackgroundTask:taskId];18     });19 }