Question

I am currently working on an application which is parsing some JSON data in the APPdelegate class when the location is changed.

My question is: ” How is the most appropriate way doing it ?” Currently when it is parsing the data the application is “frozen” until the data has been loaded.

I need some advice 🙂

Thanks

Answer 1

There are several ways of course, including NSThread, NSOperation and old-fashioned libpthread. But what I find the most convenient (especially for simple background tasks) is libdispatch also called Grand Central Dispatch.

Using dispatch queues you can quickly delegate a time-consuming task to a separate thread (or more precisely, execution queue – GCD decides whether it’s a thread or an asynchronous task). Here’s the simplest example:

// create a dispatch queue, first argument is a C string (note no "@"), second is always NULL
dispatch_queue_t jsonParsingQueue = dispatch_queue_create("jsonParsingQueue", NULL);

// execute a task on that queue asynchronously
dispatch_async(jsonParsingQueue, ^{
    [self doSomeJSONReadingAndParsing];

    // once this is done, if you need to you can call
    // some code on a main thread (delegates, notifications, UI updates...)
    dispatch_async(dispatch_get_main_queue(), ^{
        [self.viewController updateWithNewData];
    });
});

// release the dispatch queue
dispatch_release(jsonParsingQueue);

The above code will read JSON data in a separate execution queue, not blocking the UI thread. This is just a simple example and there’s a lot more to GCD, so take a look at the documentation for more info.