title: Views not redrawing when siblings change with auto layout
body: <p>I have an app whose UI is set up like this</p>
  <pre><code>V:[statusBarView][contentView][footerView]
  </code></pre>
  <p>though I did the layout in IB (see below). statusBarView and footerView have their heights pinned, and their top/bottom spaces (respectively) are flush with the parent view (the VC's view).</p>
  <p>In the screen grabs you can see that when the screen rotates and the view's redraw, the middle contentView container and it's subviews are resized and laid out correctly.</p>
  <p>I have the action for one of these buttons set to resize the (blue) footerView. My expectation, since the constraints are set up such that the bottom of the contentView is equal to the top of the footerView, is that if I resize the footer, the contentView will handle it's resizing on it's own. This is not happening. Regardless of if I make the footerView taller or shorter or move it up or down, the contentView remains unchanged.</p>
  <p>I have tried setNeedsUpdateConstraints, setNeedsLayout, etc, but they have no effect.</p>
  <p>Perhaps I'm completely missing the point of Auto Layout, or just how to implement it. Why would the views be able to get the layout correct when the window/superview changes, but not the sibling views that the constraints actually depend on?</p>
  <p>Thanks</p>
  <p><img src="https://i.stack.imgur.com/TtwxU.png" alt="Default vertical layout" />
  <img src="https://i.stack.imgur.com/Ni8bt.png" alt="Default horizontal layout" /></p>