title: UIView animation to slide down
body: <p>I'm trying to slide down an image in an UIImageView, but I don't know which combination of UIContentMode and animation property is the right one to make that happen.
  The image should always have the same size and should not be streched... all I want is, that nothing is visible first and then the frame extends and reveals the image.</p>
  
  <p>Maybe it's easier if you see what I mean:</p>
  
  <p><img src="https://i.stack.imgur.com/t0iK0.png" alt="Illustration of my Problem"></p>
  
  <p>So, it sounds rather easy, but what UIContentMode should I use for the UIImageView and what property should I animate? Thank you!</p>