title: Size classes constraint not working
body: <p>I have 2 view in viewController,</p>
  
  <p>BlueView and GreenView,</p>
  
  <p>GreenView is BlueView subview.</p>
  
  <p><a href="https://i.stack.imgur.com/vFYJU.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/vFYJU.png" alt="enter image description here"></a></p>
  
  <p><strong>BlueView constraints:</strong></p>
  
  <ul>
  <li>Trailing Space to: Superview(ViewController.view)</li>
  <li>Leading Space to: Superview(ViewController.view)</li>
  <li>BottomSpace to: Superview(ViewController.view)</li>
  <li>Top Space to: Superview(ViewController.view)</li>
  </ul>
  
  <p><strong>GreenView constraints:</strong></p>
  
  <ul>
  <li><p>Trailing Space to: Superview(BlueView)</p></li>
  <li><p>Leading Space to: Superview (BlueView)</p></li>
  <li><p>Bottom Space to: Superview (BlueView)</p></li>
  <li><p>Proportional Hight to View (ViewController.view)<br>
  (ViewController.view.height *0.5)</p></li>
  </ul>
  
  <p>It work for universal layout.</p>
  
  <p>But in size classes(wC hR), not working.</p>
  
  <p><a href="https://i.stack.imgur.com/tVRMh.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/tVRMh.png" alt="enter image description here"></a></p>
  
  <p>GreenView hight constraint not active</p>
  
  <ul>
  <li>Proportional Hight to View (ViewController.view)  </li>
  </ul>
  
  <p>Universal layout, works fine:
  <a href="https://i.stack.imgur.com/sGkMx.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/sGkMx.png" alt="enter image description here"></a></p>
  
  <p>Size classes(wC hR), not working as I expected:</p>
  
  <p><a href="https://i.stack.imgur.com/sUuBq.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/sUuBq.png" alt="enter image description here"></a></p>
  
  <p>Use IBoutlet active this constraint</p>
  
  <pre><code>- (void)viewDidAppear:(BOOL)animated{
      self.greenViewHeightConstraint.active = YES;
  }
  </code></pre>
  
  <p>It work!?</p>
  
  <p><a href="https://i.stack.imgur.com/QNcnp.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/QNcnp.png" alt="enter image description here"></a></p>
  
  <p>This constraint in size classes is illegal?</p>
  
  <p>But in viewDidAppear is legal?</p>
  
  <p>Any idea?</p>