Implementing long running tasks in background IOS

Question

I have been working on an app in which user can record video using AVFoundation and send to the server, video has maximum size up to 15M, depending on the internet speed & type it can take from 1 to 5 minutes approximately to transfer video to the server. I am transferring the recorded video to the server in the background thread so that user can continue other stuff on the app while video is being uploaded to the server.

While reading the Apple Docs for implementing long running tasks in backround, I see that only few kinds of apps are allowed to execute in the background.
e.g.

audio—The app plays audible content to the user while in the background. (This content includes streaming audio or video content using AirPlay.)

Does it qualify my app also for running the tasks in the background? or I need to transfer the video on the main thread?

Answer 1

NSOperationQueue is the recommended way to perform multi-threaded tasks to avoid blocking the main thread. Background thread is used for tasks that you want to perform while your application is inactive, like GPS indications or Audio streaming.

If your application is running in foreground, you don't need background thread at all.

For simple tasks, you can add a operation to a queue using a block:

NSOperationQueue* operationQueue = [[NSOperationQueue alloc] init];
[operationQueue addOperationWithBlock:^{
    // Perform long-running tasks without blocking main thread
}];

More info about NSOperationQueue and how to use it.

The upload process will continue while in background, but your application will be eligible to be suspended, and thus the upload may cancel. To avoid it, you can add the following code to application delegate to tell the OS when the App is ready to be suspended:

- (void)applicationWillResignActive:(UIApplication *)application {
    bgTask = [application beginBackgroundTaskWithExpirationHandler:^{

      // Wait until the pending operations finish
      [operationQueue waitUntilAllOperationsAreFinished];

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

Answer 2

From your response to Dwayne, you do not need to be able to download in background mode. Rather what you need is to do your download in another thread (background thread) beside main thread. Something like this for GCD:

    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
//        Do you download here...
    });