class1.cs

来自DoFactory的设计模式, 由于是本人根据已有代码创建,没有NETOptimized项

// Observer pattern -- Real World example  

using System;
using System.Collections;

namespace DoFactory.GangOfFour.Observer.RealWorld
{

    // MainApp test application 

    class MainApp
    {
        static void Main()
        {
            // Create investors 
            Investor s = new Investor("Sorros");
            Investor b = new Investor("Berkshire");

            // Create IBM stock and attach investors 
            IBM ibm = new IBM("IBM", 120.00);
            ibm.Attach(s);
            ibm.Attach(b);

            // Change price, which notifies investors 
            ibm.Price = 120.10;
            ibm.Price = 121.00;
            ibm.Price = 120.50;
            ibm.Price = 120.75;

            // Wait for user 
            Console.Read();
        }
    }

    // "Subject" 

    abstract class Stock
    {
        protected string symbol;
        protected double price;
        private ArrayList investors = new ArrayList();

        // Constructor 
        public Stock(string symbol, double price)
        {
            this.symbol = symbol;
            this.price = price;
        }

        public void Attach(Investor investor)
        {
            investors.Add(investor);
        }

        public void Detach(Investor investor)
        {
            investors.Remove(investor);
        }

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

        // Properties 
        public double Price
        {
            get { return price; }
            set
            {
                price = value;
                Notify();
            }
        }

        public string Symbol
        {
            get { return symbol; }
            set { symbol = value; }
        }
    }

    // "ConcreteSubject" 

    class IBM : Stock
    {
        // Constructor 
        public IBM(string symbol, double price)
            : base(symbol, price)
        {
        }
    }

    // "Observer" 

    interface IInvestor
    {
        void Update(Stock stock);
    }

    // "ConcreteObserver" 

    class Investor : IInvestor
    {
        private string name;
        private Stock stock;

        // Constructor 
        public Investor(string name)
        {
            this.name = name;
        }

        public void Update(Stock stock)
        {
            Console.WriteLine("Notified {0} of {1}'s " +
              "change to {2:C}", name, stock.Symbol, stock.Price);
        }

        // Property 
        public Stock Stock
        {
            get { return stock; }
            set { stock = value; }
        }
    }
}