title: How to resize a fixed width and height UIImageView with auto layout
body: <p>I have a view named <code>myView</code> which is always half the screen and sit at the top of screen.  </p>
  
  <p>Inside this view I added an <code>UIImageView</code> with 120x120 size which sits in center of the <code>myView</code> (horizontally and vertically). Inside the IB, to satisfy the constraints(X &amp; Y) I always need to set a fixed width and height for my image, after I set center horizontally and center vertically.  </p>
  
  <p>But with a fixed height and width, the image doesn't resize when changing the screen size. I want my image to resize when running on iPhone5 or iPhone 4s, because <code>myView</code> will resize. 
  I need something like the image should depend on the <code>myView</code> size.  </p>
  
  <p>How to actually achieve this ?</p>