title: Center a button in a navigationBar
body: <p>I would like to center a button in my navigationBar, which is currently defined as a rightBarButtonItem :</p>
  
  <pre><code>UIBarButtonItem *audioBtn = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemPlay target:self action:@selector(toggleAudioPlayback:)];
  self.navigationItem.rightBarButtonItem = audioBtn;
  [audioBtn release];
  </code></pre>