UI control in GCD Code

gistfile1.m

[NSURLConnection sendAsynchronousRequest:req 
                 queue:[[[NSOperationQueue alloc] init] autorelease] 
                 completionHandler:^(NSURLResponse *response, 
                                            NSData *data, 
                                           NSError *error) {
    NSError* err;
    NSDictionary *respJSON = [NSJSONSerialization JSONObjectWithData:data 
                                                             options:NSJSONReadingMutableContainers 
                                                               error:&err];
    dispatch_async(dispatch_get_main_queue(), ^{
        callback(respJSON);
    });
}];