title: Do I have to removeObserver in KVO manually
body: <p>I have read the <a href="https://developer.apple.com/library/ios/documentation/cocoa/conceptual/KeyValueObserving/Articles/KVOBasics.html" rel="noreferrer">apple documen</a>t about KVO, and it said:</p>
  
  <blockquote>
    <p>Note: The key-value observing addObserver:forKeyPath:options:context:
    method <strong>does not maintain strong references to the observing object</strong>,
    the observed objects, or the context. You should ensure that you
    maintain strong references to the observing, and observed, objects,
    and the context as necessary.</p>
  </blockquote>
  
  <p>The observer object not have a strong references to the observered object.</p>
  
  <p>Does this man I can not call <code>removeObserver:forKeyPath:</code> in the <code>dealloc</code> method? Can it remove the observer automatically?</p>