title: How to change the text of UIBarButtonItem programmatically?
body: <p>I've read this article:
  <a href="https://stackoverflow.com/questions/1225457/change-the-text-of-a-uilabel-uibarbuttonitem-on-a-toolbar-programmatically">Change the text of a UILabel (UIBarButtonItem) on a toolbar programmatically</a></p>
  
  <p>But it seems not working for my auto-hide toolbar?<br>
  I also tried <code>barbuttonItem.title</code> to set the text, failed too.  </p>
  
  <p>Any idea?</p>