Stock.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace DoFactory.GangOfFour.Observer.RealWorld
{
    abstract class Stock
    {
        private string _symbol; private double _price;
        private List<IInvestor> _investors = new List<IInvestor>();

        public Stock(string symbol, double price)
        {
            _symbol = symbol; _price = price;
        }

        public void Attach(IInvestor investor)
        {
            _investors.Add(investor);
        }

        public void Detach(IInvestor investor)
        {
            _investors.Remove(investor);
        }

        public void Notify()
        {
            foreach (IInvestor investor in _investors)
            {
                investor.Update(this);
            }
            Console.WriteLine("");
        }

        public double Price
        {
            get
            {
                return _price;
            }
            set
            {
                if (_price != value)
                {
                    _price = value;
                    Notify();
                }
            }
        }

        public string Symbol
        {
            get
            {
                return _symbol;
            }
        }
    }
}