title: can not receive notification of change, key value observing, KVO model-IOS
body: <p>Im registering an observer for on of my class named myClassA ( subclass of uiview ) from one of my class named UIScrollView(Sample)( a category for uiscroll view ) </p>
  
  <pre><code>@implementation UIScrollView (myClass)
      // Register an observer       
      - (void)registerAsObserver {        
           [self addObserver:[self getMyClassA] forKeyPath:@"notification" options:NSKeyValueObservingOptionNew context:nil];
      }
  </code></pre>
  
  <p>In myClassA</p>
  
  <pre><code>@implementation myClassA
  
  - (id)initWithFrame:(CGRect)frame {
      if(self = [super initWithFrame:frame]) {
          // Initialization goes here        
      }
      return self;
  }
  
  #pragma mark - Receive notification of change 
  - (void)observeValueForKeyPath:(NSString *)keyPath
                        ofObject:(id)object
                          change:(NSDictionary *)change
                         context:(void *)context {
      CGPoint newPoint    =   [[change objectForKey:NSKeyValueChangeNewKey] CGPointValue];
  
      if ( [keyPath isEqualToString:@"notification"] ) {
          [self doSomething:newPoint];
  
      }
  
  }
  </code></pre>
  
  <p>However, it seems to be that myClassA is not receiving any notification from <code>UIScrollView(myClass)</code>. After google it, i found out that the reason is the keyword <strong><em>forKeyPath</em></strong>. If i change it to <code>contentOffset</code>, everything works like charm. </p>
  
  <p>Did a quick research at <a href="http://developer.apple.com/library/ios/#documentation/cocoa/conceptual/KeyValueObserving/KeyValueObserving.html#//apple_ref/doc/uid/10000177-BCICJDHA" rel="nofollow">here</a> but still dont understand why.</p>