Multiple file queue and download

The way OperationQueue works is that the queue will observe the value of isExecuting and isFinished variables of the operation, the queue will move on to process the next operation once the current operation notifies the queue that it has finished executing.

The willChangeValue and didChangeValue methods are used to notify the queue that the value of the variable the forKey refers to the variable name has changed, once the queue receive this notification, the queue will check for the value of isExecuting and isFinished variables.

If the value of isFinished is true, then the queue will move on to the next operation. Next, we will add a custom init method for the DownloadOperation class to allow us to pass an existing URLSession, URL and an optional custom completion handler the function you want to run after the download has completed into it :.

And finally we need to override the start and cancel methods of the operation, start contains code that will be run when the queue perform the operation, and cancel contains code that will be run when the operation gets cancelled while in the mid of executing. According to Apple's documentation , you should never call super.

Your start method should also check to see if the operation itself was cancelled before actually starting the task. Now that we have implemented the DownloadOperation, we can use it download multiple files sequentially in a queue like this :. In the documentation of NSOperation , Apple mentioned that if we implemented custom data accessor ie. When you subclass NSOperation , you must make sure that any overridden methods remain safe to call from multiple threads.

If you implement custom methods in your subclass, such as custom data accessors, you must also make sure those methods are thread-safe. There might be situation where the. As explaining how to solve the reader writer problem is out of the scope of this article, I recommend referring this Stack Overflow answer. Apple's Operation class documentation. Apple's OperationQueue class documentation. Copyright fluffy. TL;DR : Just want the code? Get sample Xcode project containing the sequential download and progress UI, try them out!

Tired of fighting with Auto Layout constraints? Active 5 years, 1 month ago. Viewed 6k times. Improve this question. Community Bot 1 1 1 silver badge. Karthik Kamalakannan Karthik Kamalakannan 1 1 gold badge 10 10 silver badges 30 30 bronze badges. Add a comment. Active Oldest Votes.

If you have an IntentService which reads URLs from the supplied Intent , then all you have to do is create an Intent for each file you want to download, and send each Intent to the service, Here is a good tutorial. Improve this answer. Graham Borland Graham Borland Thank you for the suggestion! Can you please have a look at the code I have referenced in my question The Git code and let me know where to use the IntentService Please?

Launch your async tasks with: yourAsynTask. Make sure you call down this on shutdown: threadPoolExecutor. Frank Frank What's the best way to implement a download queue in Android? Attif Attif 1, 13 13 silver badges 17 17 bronze badges. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog. Who owns this outage? Building intelligent escalation chains for modern SRE. Podcast Who is building clouds for the independent developer?

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