// 客戶端（Client）
static void Main(string[] args)
{
    //我們有了三位儲(chǔ)戶，都是武林高手，也比較有錢
    Depositor huangFeiHong = new BeiJingDepositor("黃飛鴻", 3000);
    Depositor fangShiYu = new BeiJingDepositor("方世玉", 1300);
    Depositor hongXiGuan = new BeiJingDepositor("洪熙官", 2500);

    BankMessageSystem beijingBank = new BeiJingBankMessageSystem();
    //這三位開始訂閱銀行短信業(yè)務(wù)
    beijingBank.Add(huangFeiHong);
    beijingBank.Add(fangShiYu);
    beijingBank.Add(hongXiGuan);

    //黃飛鴻取100塊錢
    huangFeiHong.GetMoney(100);
    beijingBank.Notify();

    //黃飛鴻和方世玉都取了錢
    huangFeiHong.GetMoney(200);
    fangShiYu.GetMoney(200);
    beijingBank.Notify();

    //他們?nèi)齻€(gè)都取了錢
    huangFeiHong.GetMoney(320);
    fangShiYu.GetMoney(4330);
    hongXiGuan.GetMoney(332);
    beijingBank.Notify();
}

//銀行短信系統(tǒng)抽象接口，是被觀察者--該類型相當(dāng)于抽象主體角色Subject
public abstract class BankMessageSystem
{
    protected IList<Depositor> observers;

    //構(gòu)造函數(shù)初始化觀察者列表實(shí)例
    protected BankMessageSystem()
    {
        observers = new List<Depositor>();
    }

    //增加預(yù)約儲(chǔ)戶
    public abstract void Add(Depositor depositor);

    //刪除預(yù)約儲(chǔ)戶
    public abstract void Delete(Depositor depositor);

    //通知儲(chǔ)戶
    public void Notify()
    {
        foreach (Depositor depositor in observers)
        {
            if (depositor.AccountIsChanged)
            {
                depositor.Update(depositor.Balance, depositor.OperationDateTime);
                //賬戶發(fā)生了變化，并且通知了，儲(chǔ)戶的賬戶就認(rèn)為沒有變化
                depositor.AccountIsChanged = false;
            }
        }
    }
}

//北京銀行短信系統(tǒng)，是被觀察者--該類型相當(dāng)于具體主體角色ConcreteSubject
public sealed class BeiJingBankMessageSystem : BankMessageSystem
{
    //增加預(yù)約儲(chǔ)戶
    public override void Add(Depositor depositor)
    {
        //應(yīng)該先判斷該用戶是否存在，存在不操作，不存在則增加到儲(chǔ)戶列表中，這里簡(jiǎn)化了
        observers.Add(depositor);
    }

    //刪除預(yù)約儲(chǔ)戶
    public override void Delete(Depositor depositor)
    {
        //應(yīng)該先判斷該用戶是否存在，存在則刪除，不存在無操作，這里簡(jiǎn)化了
        observers.Remove(depositor);
    }
}

//儲(chǔ)戶的抽象接口--相當(dāng)于抽象觀察者角色（Observer）
public abstract class Depositor
{
    //狀態(tài)數(shù)據(jù)
    private string _name;
    private int _balance;
    private int _total;
    private bool _isChanged;

    //初始化狀態(tài)數(shù)據(jù)
    protected Depositor(string name, int total)
    {
        this._name = name;
        this._balance = total;//存款總額等于余額
        this._isChanged = false;//賬戶未發(fā)生變化
    }

    //儲(chǔ)戶的名稱，假設(shè)可以唯一區(qū)別的
    public string Name
    {
        get { return _name; }
        private set { this._name = value; }
    }

    public int Balance
    {
        get { return this._balance; }
    }

    //取錢
    public void GetMoney(int num)
    {
        if (num <= this._balance && num > 0)
        {
            this._balance = this._balance - num;
            this._isChanged = true;
            OperationDateTime = DateTime.Now;
        }
    }

    //賬戶操作時(shí)間
    public DateTime OperationDateTime { get; set; }

    //賬戶是否發(fā)生變化
    public bool AccountIsChanged
    {
        get { return this._isChanged; }
        set { this._isChanged = value; }
    }

    //更新儲(chǔ)戶狀態(tài)
    public abstract void Update(int currentBalance, DateTime dateTime);
}

//北京的具體儲(chǔ)戶--相當(dāng)于具體觀察者角色ConcreteObserver
public sealed class BeiJingDepositor : Depositor
{
    public BeiJingDepositor(string name, int total) : base(name, total) { }

    public override void Update(int currentBalance, DateTime dateTime)
    {
        Console.WriteLine(Name + ":賬戶發(fā)生了變化，變化時(shí)間是" + dateTime.ToString() + ",當(dāng)前余額是" + currentBalance.ToString());
    }
}