gistfile1.m

- (void)viewDidLoad{
    [super viewDidLoad];

    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    dispatch_async(queue, ^{
        //go fetch some data from the Iternet or DB here...
        //data received!
        dispatch_async(dispatch_get_main_queue(), ^{
          //update UI
        }
    }
}