title: UIImageView keep aspect ratio, but fit to width
body: <p>I have a UIImageView with a fixed width and height.  I don't want to change the frame of the UIImageView.  I want to have it hold an image where I keep the aspect ratio and I fit the width and let the image be either too tall, or too short for the UIImageView's frame. Like this:</p>
  
  <p><a href="https://i.stack.imgur.com/o8hEI.png" rel="noreferrer"><img src="https://i.stack.imgur.com/o8hEI.png" alt="UIImageView frame"></a></p>
  
  <p>The red is the UIImageView's frame.  The gray is the actual image as it's displayed.</p>