title: button press animation
body: <p>So I've searched a lot but I didn't find an answer for my problem. </p>
  
  <p>I want to make a button that would have two images, first image that is when button is in normal state, the other one when it is in highlighting state. The problem is that i want these images to change in animated manner, for example the first image fades out, when the second fades in. And they change in such a way that the animation time remains constant.</p>
  
  <p>The only way I thought is, to make a custom button, add couple of <code>ImageViews</code> and on button touch down event, one <code>ImageView</code> fades in, other fades out, on button touch up event, I could do the opposite.  But this method doesn't seem the most suitable.  Is there a better option that I am not seeing?</p>