关于C# 设计模式 Observer 观察者模式

using System;
using System.Collections.Generic;
using System.Text;
using System.Collections;

///Observer（观察者）模式又被称作发布－订阅（Publish-Subscribe）模式，用于定义对象间的一对多的依赖关系，
///当一个对象的状态发生改变时，所有依赖于它的对象都得到通知并被自动更新。
///add by jzh 2007-04-15
namespace DesignPattern
{
    class Subject
    {
        private ArrayList list = new ArrayList();

        private string strImportantSubjectData = "Initial";

        public string ImportantSubjectData
        {
            get
            {
                return strImportantSubjectData;
            }
            set
            {
                strImportantSubjectData = value;
            }
        }

        public void Attach(Observer o)
        {
            list.Add(o);
            o.ObservedSubject = this;
        }

        public void Detach(Observer o)
        {

        }

        public void Notify()
        {
            foreach (Observer o in list)
            {
                o.Update();
            }
        }
    }

    class ConcreteSubject : Subject
    {
        public void GetState()
        {

        }

        public void SetState()
        {

        }
    }

    abstract class Observer
    {
        protected Subject s;
        public Subject ObservedSubject
        {
            get
            {
                return s;
            }
            set
            {
                s = value;
            }
        }
        abstract public void Update();
    }

    class ConcreteObserver : Observer
    {
        private string observerName;

        public ConcreteObserver(string name)
        {
            observerName = name;
        }

        override public void Update()
        {
            Console.WriteLine("观察者 {0}: 消息 = {1}", observerName, s.ImportantSubjectData);
        }
    }

    public class Client
    {
        public static void Main(string[] args)
        {
            // 建立观察者
            ConcreteSubject s = new ConcreteSubject();
            ConcreteObserver o1 = new ConcreteObserver("a");
            ConcreteObserver o2 = new ConcreteObserver("b");

            s.Attach(o1);
            s.Attach(o2);

            // 发生变化
            s.ImportantSubjectData = "有一条新消息";

            // 通知观察者
            s.Notify();

            Console.ReadLine();
        }
    }
}