title: Insert subview behind TabBar from child view of TabBarController
body: <p>I have <code>TabBar</code> with 2 tabs. At some point, from either of the 2 tabs, I want to add a view that is visible on both tab views but behind the <code>TabBar</code>.</p>
  
  <p>So I thought, insert a subview into the <code>TabBarController</code> but below the <code>TabBar</code>.</p>
  
  <p>This works fine in principle and I have the view behind the <code>TabBar</code> but now covering my 2 tabs as I wanted. However, it doesn't actually load. Just its background loads and only <code>viewDidLoad()</code> is called, <strong>not</strong> <code>viewWillAppear()</code> or any others.</p>
  
  <p>I have also tried calling <code>addChildViewController(myVC)</code> on the <code>TabBarController</code> which has no effect, and also manually calling <code>viewWillAppear()</code> on the view controller I add which also has no effect (and I'm also dubious about whether manually calling <code>viewWillAppear()</code> is permitted or not?).</p>
  
  <p>Is what I'm trying to do possible? What am I missing? Or should I be attempting this some other way?</p>