title: UIButton: set image for selected-highlighted state
body: <p>I set an images for button's states Normal,Highlighted and Selected, but when the button in selected state and I press/highlight it I didn't see my highlighted image but just grayed picture.
  Is it possible to set an image for highlighted state when the button selected?</p>
  
  <p>my code:</p>
  
  <pre><code>[button setImage:[UIImage imageNamed:@"normal.png"] forState:UIControlStateNormal];
  [button setImage:[UIImage imageNamed:@"pressed.png"] forState:UIControlStateHighlighted];
  [button setImage:[UIImage imageNamed:@"checked.png"] forState:UIControlStateSelected];
  </code></pre>
  
  <p>when I do:</p>
  
  <pre><code>[button setSelected:YES];
  </code></pre>
  
  <p>and press the button, the "pressed.png" image doesn't select.</p>