public NSObject AddObserver(NSString aName, Action<NSNotification> notify, NSObject fromObject)
        {
            if (notify == null)
                throw new ArgumentNullException ("notify");

            var proxy = new InternalNSNotificationHandler (this, notify);

            AddObserver (proxy, postSelector, aName, fromObject);

            return proxy;
        }
        public NSObject AddObserver(NSString aName, Action <NSNotification> notify, NSObject fromObject)
        {
            if (notify == null)
            {
                throw new ArgumentNullException("notify");
            }

            var proxy = new InternalNSNotificationHandler(this, notify);

            AddObserver(proxy, postSelector, aName, fromObject);

            return(proxy);
        }