title: proportional height of view and superview autolayout
body: <p>I have a small view that I want him occupy 1/3 height of superview(same size with safe area)</p>
  
  <p>I defined leading space, trailing space, bottom space which its constant = 0 with superview.bottom.</p>
  
  <p>AND I want to make the height 1/3 of superview height to make it same look in all iphone sizes. I defined aspect ratio and changed its first item as superview.height and second item as thisview.height. of course I have defined 3:1 multiplier
  <a href="https://i.stack.imgur.com/wXQMf.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/wXQMf.png" alt="enter image description here"></a>
  <a href="https://i.stack.imgur.com/aNDv5.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/aNDv5.png" alt="enter image description here"></a></p>
  
  <p>But it doesnt work it gives following error</p>
  
  <blockquote>
    <p>Terminating app due to uncaught exception 'NSGenericException',
    reason: 'Unable to install constraint on view.  Does the constraint
    reference something from outside the subtree of the view?  That's
    illegal.</p>
  </blockquote>
  
  <p>Come on!! why doesnt it work? this is not that complex compared to all other stuff. 
  Also how can I complish this on interface. (not in code) I would like to see it on xcode with all other screensizes in preview tab.</p>
  
  <p>Thanks a lot for your time.</p>