title: Navigation bar show/hide
body: <p>I have an app with a navigation bar consisting of 2 bar buttons. I would like to hide and show this navigation bar when a user double taps the screen.</p>
  
  <p>Initially, the navigation bar should be hidden. When a user double taps the screen, the navigation bar should come up with an animation, like what can be seen in the iPhone's photo gallery.</p>
  
  <p>How can i do something this? Suggestions are always appreciated.</p>