title: Change constraints of UINavigationBar in UINavigationController
body: <p>Apple says in its <a href="https://developer.apple.com/library/ios/documentation/UIKit/Reference/UINavigationController_Class/#//apple_ref/occ/instp/UINavigationController/navigationBar" rel="nofollow">Documentation</a>: </p>
  
  <blockquote>
    <p>It is permissible to customize the appearance of the navigation bar using the methods and properties of the <strong>UINavigationBar</strong> class but you must never change its <strong>frame</strong>, <strong>bounds</strong>, or <strong>alpha</strong> values or modify its view hierarchy directly. </p>
  </blockquote>
  
  <p>They never strictly mention that changing constraints is not allowed but I'm assuming it falls under the same criteria as of changing the frame.</p>
  
  <p>I would need this for a messages app in order to achieve the translucency effect under the iMessage standard top bar. What I currently have is a <code>UINavigationController</code> embedded in a <code>MSMessagesAppViewController</code> with the <code>topAnchor</code> set underneath the <code>topLayoutGuide</code>. This prevents me from achieving the effect but places the navigation bar below the top bar accordingly. If I set the constraints to just attach to the topAnchor, the Navigation bar is hidden in the extended view. Changing the constraints of the <code>UINavigationBar</code> here could solve the problem. </p>
  
  <p>Am I allowed to change the constraints of the <code>UINavigationBar</code> and if not, any other solutions for this issue? For any further information just tell me. </p>