title: How to disable back button in navigation bar
body: <p>Is there any official way how to set <code>UIBarButtonItem.enabled</code> property? I tried to set a backButtonItem in previous controller. But <code>enabled</code> property is ignored.</p>
  
  <p>More in this simple <a href="https://www.dropbox.com/s/vvnyalf69l4a621/BackButton.zip?dl=0" rel="noreferrer">example project</a>.</p>
  
  <p>I don't want to some solution like "make your own leftBarButtonItem and set its alpha ..."</p>
  
  <p>Edit: I don't want to hide it, only disable it with dimmed colour and disabled user interaction. It's exactly the same behaviour as for disabled <code>leftBarButtonItem</code>.</p>