title: fade between two UIButton images
body: <p>i want to fade between two UIButton images for the purpose of setting favorites in a UITableView.</p>
  
  <p>Currently the transition is done without effect - it just changes the images directly on click/touch:</p>
  
  <pre><code>trans_img = [UIImage imageNamed:@"fav_on.png"];
  
  NSArray *subviews = [owningCell subviews];
  UIButton *favbutton = [subviews objectAtIndex:2];
  
  favbutton.imageView.animationImages =
  [NSArray arrayWithObjects:trans_img,
   nil];
  
  [favbutton.imageView startAnimating];
  </code></pre>
  
  <p>Everything I found was a transition between UIViews :(</p>
  
  <p>It would be nice if the image fav_off gets smoothly changed into fav_on and the other way round like a fadein/fadeout.</p>