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PONSURLConnection vs. NSData + GCD
 

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    <p><code>NSData</code> has always had a very convenient method called <code>+dataWithContentsOfURL:options:error:</code>. While convenient, it also blocks execution of the current thread, which meant it was basically useless for production code (Ignoring <code>NSOperation</code>). I used this method so infrequently, I completely forgot that it existed. Until recently.</p> <p>The way I've been grabbing data from the tubes is the standard <code>NSURLConnectionDelegate</code> approach: Write a download class that handles the various <code>NSURLConnectionDelegate</code> methods, gradually build up some data, handle errors, etc. I'll usually make this generic enough to be reused for as many requests as possible.</p> <p>Say my typical downloader class runs somewhere in the ballpark of 100 lines. That's 100 lines to do asynchronously what <code>NSData</code> can do synchronously in one line. For more complexity, that downloader class needs a delegate protocol of its own to communicate completion and errors to its owner, and the owner needs to implement that protocol in some fashion.</p> <p>Now, enter Grand Central Dispatch, and I can do something as fantastically simple as:</p> <pre><code>dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^(void) { NSData* data = [NSData dataWithContentsOfURL:someURL]; // Process data, also async... dispatch_async(dispatch_get_main_queue(), ^(void) { // Back to the main thread for UI updates, etc. }); }); </code></pre> <p>And I can throw that sucker in anywhere I want, right in-line. No need for a download class, no need to handle connection delegate methods: Easy async data in just a few lines. The disparity between this approach and my pre-GCD approach is of a magnitude great enough to trigger the Too Good to be True Alarm.</p> <p>Thus, my question: Are there any caveats to using <code>NSData</code> + GCD for simple data download tasks instead of <code>NSURLConnection</code> (Assuming I don't care about things like download progress)?</p>
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