title: Trying to programmatically add a button to UINavigationController but it never shows up
body: <p>I've programmatically created some UINavigationControllers and added them to a UITabBarController.  Everything seems to work fine but I wanted to add a cancel button to the navigation controller but it never shows up.  I've tried multiple ways but I can't seem to affect the display of the navigation items at all and I've followed multiple examples from here and other sites but nothing happens.</p>
  
  <pre><code>MyTableViewController *mtvc = [[MyTableViewController alloc] init]; 
  UINavigationController *myNavController = [[[UINavigationController alloc] initWithRootViewController:mtvc] autorelease];
  myNavController.navigationBar.barStyle = UIBarStyleBlackOpaque;  // this works
  [mtvc release];
  
  // TODO: figure out why added buttons aren't showing
  UIBarButtonItem *closeButton = [[[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemCancel target:self action:@selector(shutDown)] autorelease]; 
  myNavController.navigationItem.leftBarButtonItem = closeButton;  // never shows up
  </code></pre>
  
  <p>I also tried adding the button this way</p>
  
  <pre><code>[myNavController.navigationItem setLeftBarButtonItem:closeButton animated:NO];  // also doesn't do anything
  </code></pre>
  
  <p>I started getting frustrated so I also tried some other things just to see if I could affect anything, but to no avail</p>
  
  <pre><code>myNavController.title = @"test";  // does nothing
  </code></pre>
  
  <p>I've tried doing it before and after the navigations controllers were added to the UITabBarController and that didn't help.
  I've also tried rightBarButtonItem and tried using initWithTitle: instead of initWithBarButtonSystemItem.  </p>
  
  <p>Would someone please illuminate me?  Clearly, I'm doing this the wrong way. </p>