swiftでKVO

1. 監視対象のプロパティに dynamic 修飾子をつける
2. Observer は NSObject を継承している必要がある

dynamic var fbNativeAd:FBNativeAd?        

addObserver(self, forKeyPath: "fbNativeAd", options: [.New, .Old], context: nil)
  
deinit {
     removeObserver(self, forKeyPath: "fbNativeAd")
 }
    
override internal func observeValueForKeyPath(
    keyPath: String?,
    ofObject object: AnyObject?,
    change: [String : AnyObject]?,
    context: UnsafeMutablePointer<Void>)
    {
        print("hoge-----")
        if( keyPath=="fbNativeAd"){
        }
}