Observer Pattern using C# Delegate

class Program

    {

        static void Main(string[] args)
        {
            Stock stock1 = new Stock("IPCL");
            stock1.Price = 27.10M;

            StockObserver1 so1 = new StockObserver1();

            StockObserver2 so2 = new StockObserver2();
             //Register Observers  with the subject
            stock1.Registor(so1);

            stock1.Registor(so2);

            stock1.Price = 31.59M;
             //Unregister Observers (StockObserver1)  from the subject

            stock1.UnRegistor(so1);

            stock1.Price = 41.59M;

            Console.Read();

        }

    }

class Stock : ISubject

    {

        public string Symbol { get; set; }

        private Decimal price;

        public Stock(string str)

        {

            Symbol = str;

        }
       //Declare an event of type delegate of void method with string parameter 
        public event Action<string> PriceChanged;

        public virtual void OnPriceChanged()

        {

            if (PriceChanged != null)

                PriceChanged(string.Format("Stock {0} price changed {1}",

                    Symbol, Price.ToString()));

        }

        public Decimal Price

        {

            get { return price; }

            set

            {

                if (price == value)

                    return;

                price = value;

                OnPriceChanged();

            }

        }

        public void Registor(IObserver obj)

        {
         //attaching to the delegate with observer update method

            PriceChanged +=  obj.update ;

        }

        public void UnRegistor(IObserver obj)

        {
            //dettaching the delegate with observer update method

            PriceChanged -= obj.update;

        }

    }

    interface IObserver

    {

         void update(string obj);

    }

    interface ISubject

    {

         void Registor(IObserver obj);

         void UnRegistor(IObserver obj);

    }

    public class StockObserver1 : IObserver

    {

        public void update(string obj)

        {

            Console.WriteLine("StockObserver1 stok changed" + obj);

        }

    }

    public class StockObserver2 : IObserver

    {

        public void update(string obj)

        {

            Console.WriteLine("StockObserver2 stok changed" + obj);

        }

    }