title: UIButton image asynchronously
body: <p>I have a bunch of UIButton in a UIScrollView and each UIButton takes an image from a URL. What is the easiest way so that the image will be loaded asynchronously?</p>
  
  <p>For example, the usual way is:</p>
  
  <pre><code>[button setImage:[UIImage imageWithData:data] forState:UIControlStateNormal];
  </code></pre>
  
  <p>but this blocks the UI, I don't want it to</p>