title: Remove Array Controller observer
body: <p>Observer added for array controllers are not removed.
  Code for adding :</p>
  
  <pre><code>[self.arrayController addObserver:self
                         forKeyPath:@"selectionIndexes"
                            options:NSKeyValueObservingOptionNew
                            context:nil];
  </code></pre>
  
  <p>Code to remove observer :</p>
  
  <pre><code>@try {
      //[self removeObserver:self forKeyPath:@"selectionIndexes"];
      [self.arrayController removeObserver:self forKeyPath:@"selectionIndexes"];
  }
  @catch (NSException *exception) {}
  </code></pre>
  
  <p>Even after removing observers its not effective, and <code>observeValueForKeyPath</code> is getting invoked. What am I doing wrong here ? </p>