title: How to Change Background image of a UIButton?
body: <p>I'm creating hundreds of dynamic <code>UIButtons</code> in my application. While creating these <code>UIButtons</code> I gave a tag to each one.
  What I want to do is to be able to change the background image of the <code>UIButton</code> on click. 
  If I have a <code>UIButton</code> with a tag than how can I change the background image of the <code>UIButton</code>?</p>