title: Change UITextField background when editing begins
body: <p>I'd like to change the background image of a UITextField when it becomes the firstResponder to show the user that it has focus, similar to the :active or :focus pseudo-classes in CSS.</p>
  
  <p>I'm guessing that I may need to do this programmatically; so any help is greatly appreciated.</p>
  
  <p>-Giles</p>