iphone - beginBackgroundTaskWithExpirationHandler

Question

我正在制作一个应用程序，音频将在后台播放。在以下代码中，bgTask 未声明。 bgTask 应该是一个什么样的对象？

- (void)applicationDidEnterBackground:(UIApplication *)application 
{
    UIApplication  *app = [UIApplication sharedApplication];
    bgTask = [app beginBackgroundTaskWithExpirationHandler:^{ 
        [app endBackgroundTask:bgTask]; 
        bgTask = UIBackgroundTaskInvalid;
    }];

    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{});

    [app endBackgroundTask:bgTask]; 
    bgTask = UIBackgroundTaskInvalid;
}

Answer 1

在赋值之前需要声明bgTask:

UIBackgroundTaskIdentifier bgTask = 0;