title: How to add a notification for pop view controller in iphone application?
body: <p>I have seen the sample application of iPhone MP-movie player - controller.</p>
  
  <p>They have added a notification on the sample code.</p>
  
  <pre><code>// Register to receive a notification that the movie is now in memory and ready to play
  [[NSNotificationCenter defaultCenter] addObserver:self 
                   selector:@selector(moviePreloadDidFinish:) 
                   name:MPMoviePlayerContentPreloadDidFinishNotification 
                   object:nil];
  </code></pre>
  
  <p>In above code, When MPMoviePlayerController finishes loading, it invokes moviePreloadDidFinish method.</p>
  
  <p>Similarly, I want to fire an method when user press back button from navigation bar, (back to previous view controller through navigation controller ).</p>
  
  <p>I don't know how to add a notification for that.</p>