GCD and async NSURLConnection

Question

I know that if I create an NSURLConnection (standard async one), it will call back on the same thread. Currently this is on my main thread. (work fine too).

But i\'m

Answer 1

First off, your block and every variable you use within it will get copied to GCD, so the code will not be executed on your thread but on the global queue.

If you want to get your data back on the main thread, you can nest an async call after your data has been fetched:

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:@"www.stackoverflow.com"]];
    NSURLResponse *response;
    NSError *error;
    NSData *data = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&error];
    if (error) {
        // handle error
        return;
    }
    dispatch_async(dispatch_get_main_queue(), ^{
        // do something with the data
    });
});

But why not use NSURLConnection's built in asynchronous support? You need an NSOperationQueue, but if you are doing alot of network fetches it is the way to go anyway:

NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:@"www.stackoverflow.com"]];
[NSURLConnection sendAsynchronousRequest:request
                                   queue:self.queue // created at class init
                       completionHandler:^(NSURLResponse *response, NSData *data, NSError *error){
                           // do something with data or handle error
                       }];

Personally, I use a library like AFNetworking or ASIHTTPRequest to make networking even easier, which both support blocks (the former utilizes GCD and is a bit more modern).