beginBackgroundTaskWithExpirationHandler

I am making an application where audio will play in the background. In the following code, bgTask is undeclared. What kind of object should bgTask be?

- (void)applicationDidEnterBackground:(UIApplicat开发者_开发问答ion *)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;
}

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You need to declare bgTask before you assign:

UIBackgroundTaskIdentifier bgTask = 0;

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I cannot comment on previous answers, however to initialize UIBackgroundTaskIdentifier you should not set it to nil or 0. You should set it to:

UIBackgroundTaskInvalid

In the documentation UIBackgroundTaskInvalid says it should be used to initialize variables or to check for errors.

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You are using the bgTask in the block so you have to declare it like this..

__block UIBackgroundTaskIdentifier bgTask = 0;

__block will allow this variable to use in the block method. And its have double underscore.