title: iphone get back button text
body: <p>Sorry for the another newbie question.</p>
  
  <p>I tried to get the back button text value in viewDidLoad but it always displays null when I navigate through controllers.</p>
  
  <pre><code>NSLog(@"-----------&gt; %@ ", self.navigationItem.backBarButtonItem.title);
  </code></pre>
  
  <p>How to get the back button text value?</p>