iOS start background.m

iOS_start_background.m

- (void)applicationDidEnterBackground:(UIApplication *)application
{
  UIApplication* app = [UIApplication sharedApplication];
  bgTask = [app beginBackgroundTaskWithExpirationHandler:^{
      [app endBackgroundTask:bgTask];
      bgTask = UIBackgroundTaskInvalid;
  }];
  // Start the long-running task and return immediately.
  dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, NULL), ^{
      // Do the work associated with the task.
      [app endBackgroundTask:bgTask];
      bgTask = UIBackgroundTaskInvalid;
    });
}