Can I start an NSOperation inside of another NSOperation without a queue?

Question

My application gets the current device location, POSTs this to my server, and returns a dictionary to be displayed in a table view. Currently I am using the CLLocationManager delegate methods and AFJSONRequestOperation (AFNetworking's retrieve-data-through-NSURLConnection-in-NSOperation class) to do the job, but this functionality is inside one view controller method and I'd like to be able to reuse this across other view controllers.

I am planning to make my own NSOperation subclass, but first I wanted to know if there are any unseen pitfalls in having NSOperations (AFJSONRequestOperation) start inside of another NSOperation. Does this work as expected or should I find a way to make a queue with dependencies among the operations?

Answer 1

Scheduling a NSULRL connection operation within a NSOperation will fail unless you schedule it on the main run loop. AFJSONOperation (or any subclass of AFURLOperation) will succeed because under the hood, AFNetworking operations are scheduled on their own NSOperationQueue and on a custom run loop.

So - Yes. Go for it. I use NSOperation subclasses to isolate all of my worker processes. It is much cleaner than flat out GCD in the middle of your VCs or Models.

Caveat - Since all AFNetworking operations are block based and return asynchronously, your NSOperation subclass will need to be concurrent. Apple provides a detailed description of how to build this in their docs for Concurrent NSOperation Subclasses

Optionally - you could just skip building a concurrent NSOperation subclass, and fire your network operation synchronously from within your NSOperation since you're already off of the main queue.

Answer 2

All the NSOperation stuff uses GCD under the hood, and GCD has no issues with nested dispatch_async calls, so I doubt nesting NSOperations will cause you problems as long as your logic is correct.