应用后台长运行

- (void)applicationDidEnterBackground:(UIApplication *)application

{

    

    UIApplication* app = [UIApplicationsharedApplication];

    

    UIBackgroundTaskIdentifier__block bgTask = [app beginBackgroundTaskWithExpirationHandler: ^{

        dispatch_async(dispatch_get_main_queue(), ^{

            [app endBackgroundTask:bgTask];

            bgTask = UIBackgroundTaskInvalid;

        });

    }];

}