title: Bottom layout guide length issue with tabbar after pushing
body: <p>So my problem is related to auto-layout and the bottom layout guide.</p>
  
  <p>Here's the design of the app:</p>
  
  <blockquote>
    <p>UITabBarController</p>
    
    <blockquote>
      <p>^-- Tab1: NavigationController with VC1 as root</p>
      
      <blockquote>
        <p>^-- VC2 is pushed and hides the tab bar (full screen, top layout is situated under the nav bar, bottom layout should be the lowest pixel).</p>
      </blockquote>
    </blockquote>
  </blockquote>
  
  <p>When VC2 is pushed, the bottom layout guide is 49 points length during a small amount of time and then it's 0.</p>
  
  <p>During this time, my subviews which are constrained to this bottom guide are positioned incorrectly. </p>
  
  <p>When the guide is then correctly set to 0 (by the navigation controller itself, there's no code from me regarding this), the subviews positions are then perfect.</p>
  
  <p><img src="https://i.imgur.com/2pdQCCz.gif" alt="cast"></p>
  
  <p>This does not happen on iOS 7.x (the app supports 7.0+)... I'm pretty sure that's a iOS 8 bug and I was looking for a workaround, but I could not find something that fixes this.</p>
  
  <p>I tried to solve the issue forcing the navigation controllers'view to layout in view(Will/Did)LayoutSubviews, but it did not help. </p>
  
  <p>I saw <a href="https://stackoverflow.com/questions/21850831/constraint-to-bottom-layout-guide-with-tabbar-issue">this post</a> is related but the suggested solution does not work.
  Presenting the VC2 modally solves the issue but that's not acceptable.</p>
  
  <ul>
  <li><a href="http://youtu.be/jk-q2jO9Rio" rel="nofollow noreferrer">Here's a video showing the issue</a></li>
  <li>And I created a <a href="https://github.com/RomainBoulay/iOS8-BottomLayoutGuideIssue" rel="nofollow noreferrer">small project here</a> that contains this bug.</li>
  </ul>
  
  <p>Thanks in advance for your help, let me know if you need more explanations</p>