title: Hiding UINavigationItem's bar button
body: <p>I have added a <code>BarButton</code> item to the left of the <code>nav.bar</code> through Interface Builder and in the code I want this only to show in my table view's edit mode. But I didn't find any hidden property to set the <code>leftBarButtonItem</code> (like: <code>self.navigationItem.leftBarButtonItem.hidden = YES</code>). </p>
  
  <p>I can only set <code>enabled</code> property. Anybody know how to control the hide and show property of the <code>leftBarButtonItem</code>, please help.</p>