title: Show/Hide barButtonItem
body: <p>I'm trying to show/hide a <code>UIBarButtonItem</code>. I added a <code>barButton</code> to the right side in the <code>storyboard</code>. Then in <code>viewDidLoad</code>, I made the <code>rightBarButtonItem</code> to <code>nil</code>. Later on, I set it to the <code>button</code> I added in the <code>storyboard</code>. Here's my code:</p>
  
  <pre><code>// Right barButtonItem added in storybord:
  @IBOutlet weak var deleteBarButton: UIBarButtonItem! 
  
  // viewDidLoad
  self.navigationItem.rightBarButtonItem = nil
  
  // Later on...
  self.navigationItem.rightBarButtonItem = self.deleteBarButton
  </code></pre>
  
  <p>When I set <code>self.deleteBarButton</code> to the <code>rightBarButtonItem</code>, nothing happens. It doesn't show it. What am I doing wrong, and what's the correct/most efficient way to show/hide a <code>barButtonItem</code>?</p>
  
  <p><strong>Update</strong></p>
  
  <p>I tried the following:</p>
  
  <pre><code>self.deleteBarButton.hidden = true
  </code></pre>
  
  <p>But I get the following error:</p>
  
  <blockquote>
    <p><code>UIBarButtonItem</code> does not have a member named 'hidden'</p>
  </blockquote>