title: MonoTouch NSNotificationCenter.DefaultCenter.AddObserver now obsolete?
body: <p>I'm just wondering what the modern equivalent of:</p>
  
  <pre><code>NSNotificationCenter.DefaultCenter.AddObserver("UIDeviceOrientationDidChangeNotification", receivedRotate);
  </code></pre>
  
  <p>would be. It says its obsolete and that I should use AddObserver, but I'm not sure what to use for the IntPtr context var.</p>