CODEWITHSUNDEEP
iosobjective-c-blocksgrand-central-dispatch
yannis
yannis

Reputation: 395

Keep a dispatch queue running for 5 sec after moving to the background

I am using a serial dispatch queue to serialize some network requests when the user moves the app to the background. 

- (void)applicationDidEnterBackground:(UIApplication *)application
{
    dispatch_queue_t opQ = dispatch_queue_create("com.myapp.network", NULL);
    dispatch_async(opQ, ^{
        [self sendNetworkData1];
        [self sendNetworkData2];
        [self sendNetworkData3];
    });
}

The problem is that when they run on this queue I have created, the app doesn't stay active even for the 5 seconds it is supposed to.

On the contrary, when I send the same requests outside of a queue, they are being sent for approximately 8 sec. but the app crashes afterwards. 

- (void)applicationDidEnterBackground:(UIApplication *)application
{
        [self sendNetworkData1];
        [self sendNetworkData2];
        [self sendNetworkData3];
}

I would also like to write the remaining ones on the disk, so that they can be sent the next time the user opens the app.

What's the best way to implement this?

Upvotes: 2

Views: 1250

Answers (1)

Sean Lynch
Sean Lynch

Reputation: 223

When the application enters the background if it requires additional time to complete some task you will want to notify the OS of that. The detailed documentation is here: http://developer.apple.com/library/ios/#DOCUMENTATION/iPhone/Conceptual/iPhoneOSProgrammingGuide/ManagingYourApplicationsFlow/ManagingYourApplicationsFlow.html. Here's a quick and dirty patch.

- (void)applicationDidEnterBackground:(UIApplication *)application
{
     __block UIBackgroundTaskIdentifier backgroundTask; //Create a task object

    backgroundTask = [application beginBackgroundTaskWithExpirationHandler: ^ {
        [application endBackgroundTask:background_task]; 
        backgroundTask = UIBackgroundTaskInvalid; //Set the task to be invalid
     }];

    dispatch_queue_t opQ = dispatch_queue_create("com.myapp.network", NULL);
    dispatch_async(opQ, ^{
        [self sendNetworkData1];
        [self sendNetworkData2];
        [self sendNetworkData3];
        [application endBackgroundTask:background_task]; 
        backgroundTask = UIBackgroundTaskInvalid; //Set the task to be invalid
    });
}

The bottom line is that you notify that the application needs to run in the background with beginBackgroundTaskWithExpirationHandler: THen when your done you call endBackgroundTask: to notify the OS that you are finished processing in the background. And finally make sure that you reset the backgroundTask variable to UIBackgroundTaskInvalid.

Upvotes: 2

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