title: Change the alpha value of the navigation bar
body: <p>Is this possible?</p>
  
  <p>I want to change the alpha value of the navigation bar in my view controller (in an animation), but if I do <code>self.navigationController.navigationBar.alpha = 0.0;</code>, the portion of the screen the navigationBar took up totally disappears and leaves a black box, which is not what I'd like (I'd prefer it to be the color of <code>self.view</code>'s background).</p>