title: iPhone - difference between topViewController and other forms
body: <p>I am on a delegate of a NavigationControl based app.</p>
  
  <p>when I try to access the rootViewController using</p>
  
  <pre><code>RootViewController *rootViewController = (RootViewController *)[navigationController topViewController];
  </code></pre>
  
  <p>to run a method, it crashes, saying the method is "unknown" on the rootViewController.</p>
  
  <p>When I access the rootViewController using this</p>
  
  <pre><code>RootViewController *rootViewController = (RootViewController *)[navigationController.viewControllers objectAtIndex:0];
  </code></pre>
  
  <p>it works. </p>
  
  <p>Which object is the first line accessing?</p>
  
  <p>thanks</p>