         }
 
         //Unobserving AudioItem's property
-        for keyPath in AudioItem.KVOProperties {
+        for keyPath in AudioItem.ap_KVOProperties {
             item.removeObserver(self, forKeyPath: keyPath)
         }
 

        }

        //Observing AudioItem's property
        for keyPath in AudioItem.KVOProperties {
            item.addObserver(self, forKeyPath: keyPath, options: .New, context: nil)
        }



extension AudioItem {
    /// The list of properties that is observed through KVO.
    private static var ap_KVOProperties: [String] {
        return ["artist", "title", "album", "trackCount", "trackNumber", "artworkImage"]
    }
}
