title: PNG alpha channel on UIButton (iPad)
body: <p>I am relatively new to iPad programming in cocoa touch.</p>
  
  <p>I have a PNG with an alpha channel. I want to overlay it as a subview on a UIButton so that it looks as though the Button has a border around it. (Alpha channel is the centre of the image so the user must still see through it).</p>
  
  <p>I can't seem to find a way to display the alpha channel correctly. The centre still displays as opaque white.</p>
  
  <p>If I can't do that, how would I go about drawing a border around a UIButton? Subclass UIButton and override -drawRect? Keep in mind that the buttons are programmatically (dynamically) added, as well as the borders. (I don't want to remove the button in order to add the border.) The alpha - solution would be preferable because then I can overlay the border image on the superview (scroll view) and just set the offset to correspond to a button.</p>