title: Does NSNotificationCenter removeObserver: deregister a VC from receiving MemoryWarning Notifications?
body: <p>I just stumbled about an issue in my app: I tested the <code>didReceiveMemoryWarning</code> calls to an <code>UIViewController</code> including the follow-up calls for <code>viewDidUnload</code>. </p>
  
  <p>This used to work fine in older versions of my app, but was not working now within iPhone Simulator: 
  <code>didReceiveMemoryWarning</code> was just not called any more.</p>
  
  <p>This was caused by calling <code>[NSNotificationCenter defaultCenter] removeObserver:self]</code> in <code>viewWillDisappear</code> (self being the UIViewController) to unregister for some lifecycle notifications I did add in <code>viewDidAppear</code>.</p>
  
  <p>That global <code>removeObserver:</code> call did not only remove my added notifications, but apparently also the system's UIApplicationDidReceiveMemoryWarningNotification notification caused the UIViewController's <code>didReceiveMemoryWarning</code> being called.</p>
  
  <p>Is this behaviour by design? I could not find a reference/document which was pointing out, that calling <code>removeObserver:</code> within a UIViewController breaks the standard memoryWarning handling.</p>