title: Transparent UITabBarController with changeable view in background
body: <p>I want to have a <code>UITabBarController</code>, which is has an alpha of 0.5, whose transparency allows you to see a view in the background. The background view has to be accesible and changeable.</p>
  
  <p>I'm able to add the background using this technique: <a href="https://gist.github.com/1157542" rel="nofollow">https://gist.github.com/1157542</a></p>
  
  <p>It's a <code>Category</code> which adds a subview to the <code>UITabBarController</code>, and sends the subview to the back. However, because it's a category, I can't make the subview a property. So I can't really access it. </p>
  
  <p>Is there a way to make this background view more flexible and accessible? So I could, for instance, add other subviews to it easily from any of the tab bar controller's view controllers?</p>