title: Behavior changes for updateViewConstraints in iOS 8
body: <p>I notice some small graphical glitches while testing one of my app under iOS 8: some UIViews elements are not in the right place, others have not the right size.</p>
  
  <p>In a first step, I use storyboard, Auto-Layout and constraints. Then I programmatically tune constraints to perfectly suits devices' screen size, using <code>updateViewConstraints</code>.</p>
  
  <p>Perfect on iOS 7 but with some glitches on iOS8 as on following picture:
  ./Users/dominiquevial/Documents/Informatique/Dev/Novae Marathon/_log/captures/iOS8 - iPhone 6/pause.png</p>
  
  <p>After investigation I found the problem: <code>updateViewConstraints</code> is not called. I don't understand why, maybe due to some optimizations...</p>
  
  <p>Correcting this problem is easy :</p>
  
  <ol>
  <li>use <code>viewWillLayoutSubviews</code> in place of <code>updateViewConstraints</code></li>
  <li>or add call to <code>setNeedsUpdateConstraints</code> in <code>viewWillAppear</code></li>
  </ol>
  
  <p>Which way is the best one ?</p>