title: how to change the multiplier height of uiview programmatically in swift4
body: <p>I have created my viewController with the storyboard.
  I have like 3 subviews. I used the multiplier in storyboard to fix the height which is proportional to the main view Height. Let say: </p>
  
  <pre><code>Subview1.height = 0.2× height
  Subview2.height = 0.5× height
  Subview3.height = 0.3× height
  </code></pre>
  
  <p>(This just an example)
  I want now to change the height programmatically.
  I look for a solution like this: </p>
  
  <pre><code>self.Subview1.frame.size.height = 0.5 × self.view.frame.size.height
  </code></pre>
  
  <p><strong>UPDATE</strong>
  the solution is to link the constraint from the storyboard to the custom class then a apply this solution:</p>
  
  <p><a href="https://stackoverflow.com/questions/19593641/can-i-change-multiplier-property-for-nslayoutconstraint">Can I change multiplier property for NSLayoutConstraint?</a></p>