/// <summary>
 /// 抽象主題類
 /// </summary>
 public abstract class Subject
 {
 private IList<Observer> observers = new List<Observer>();

 /// <summary>
 /// 增加觀察者
 /// </summary>
 /// <param name="observer"></param>
 public void Attach(Observer observer)
 {
  observers.Add(observer);
 }

 /// <summary>
 /// 移除觀察者
 /// </summary>
 /// <param name="observer"></param>
 public void Detach(Observer observer)
 {
  observers.Remove(observer);
 }

 /// <summary>
 /// 向觀察者（們）發(fā)出通知
 /// </summary>
 public void Notify()
 {
  foreach (Observer o in observers)
  {
  o.Update();
  }
 }
 }

 /// <summary>
 /// 抽象觀察者類，為所有具體觀察者定義一個(gè)接口，在得到通知時(shí)更新自己
 /// </summary>
 public abstract class Observer
 {
 public abstract void Update();
 }

 /// <summary>
 /// 具體觀察者或具體通知者，將有關(guān)狀態(tài)存入具體觀察者對(duì)象；在具體主題的內(nèi)部狀態(tài)改變時(shí)，給所有登記過(guò)的觀察者發(fā)出通知。具體主題角色通常用一個(gè)具體子類實(shí)現(xiàn)。
 /// </summary>
 public class ConcreteSubject : Subject
 {
 private string subjectState;

 /// <summary>
 /// 具體觀察者的狀態(tài)
 /// </summary>
 public string SubjectState
 {
  get { return subjectState; }
  set { subjectState = value; }
 }
 }

 /// <summary>
 /// 具體觀察者，實(shí)現(xiàn)抽象觀察者角色所要求的更新接口，已是本身狀態(tài)與主題狀態(tài)相協(xié)調(diào)
 /// </summary>
 public class ConcreteObserver : Observer
 {
 private string observerState;
 private string name;
 private ConcreteSubject subject;

 /// <summary>
 /// 具體觀察者用一個(gè)具體主題來(lái)實(shí)現(xiàn)
 /// </summary>
 public ConcreteSubject Subject
 {
  get { return subject; }
  set { subject = value; }
 }

 public ConcreteObserver(ConcreteSubject subject, string name)
 {
  this.subject = subject;
  this.name = name;
 }

 /// <summary>
 /// 實(shí)現(xiàn)抽象觀察者中的更新操作
 /// </summary>
 public override void Update()
 {
  observerState = subject.SubjectState;
  Console.WriteLine("The observer's state of {0} is {1}", name, observerState);
 }
 }

 class Program
 {
 static void Main(string[] args)
 {
  // 具體主題角色通常用具體自來(lái)來(lái)實(shí)現(xiàn)
  ConcreteSubject subject = new ConcreteSubject();

  subject.Attach(new ConcreteObserver(subject, "Observer A"));
  subject.Attach(new ConcreteObserver(subject, "Observer B"));
  subject.Attach(new ConcreteObserver(subject, "Observer C"));

  subject.SubjectState = "Ready";
  subject.Notify();

  Console.Read();
 }
 }

 /// <summary>
 /// 抽象觀察者
 /// </summary>
 public interface ISubject
 {
 void Notify();
 }

 /// <summary>
 /// 工作崗位，作為這里的觀察者的抽象
 /// </summary>
 public abstract class JobStation
 {
 public abstract void Update();
 }

 /// <summary>
 /// 具體主題，這里是客戶
 /// </summary>
 public class Customer : ISubject
 {
 private string customerState;

 private IList<JobStation> observers = new List<JobStation>();

 /// <summary>
 /// 增加觀察者
 /// </summary>
 /// <param name="observer"></param>
 public void Attach(JobStation observer)
 {
  this.observers.Add(observer);
 }

 /// <summary>
 /// 移除觀察者
 /// </summary>
 /// <param name="observer"></param>
 public void Detach(JobStation observer)
 {
  this.observers.Remove(observer);
 }

 /// <summary>
 /// 客戶狀態(tài)
 /// </summary>
 public string CustomerState
 {
  get { return customerState; }
  set { customerState = value; }
 }

 public void Notify()
 {
  foreach (JobStation o in observers)
  {
  o.Update();
  }
 }
 }

 /// <summary>
 /// 會(huì)計(jì)
 /// </summary>
 public class Accountant : JobStation
 {
 private string accountantState;
 private Customer customer;

 public Accountant(Customer customer)
 {
  this.customer = customer;
 }

 /// <summary>
 /// 更新狀態(tài)
 /// </summary>
 public override void Update()
 {
  if (customer.CustomerState == "已付款")
  {
  Console.WriteLine("我是會(huì)計(jì)，我來(lái)開具發(fā)票。");
  accountantState = "已開發(fā)票";
  }
 }
 }

 /// <summary>
 /// 出納
 /// </summary>
 public class Cashier : JobStation
 {
 private string cashierState;
 private Customer customer;

 public Cashier(Customer customer)
 {
  this.customer = customer;
 }

 public override void Update()
 {
  if (customer.CustomerState == "已付款")
  {
  Console.WriteLine("我是出納員，我給登記入賬。");
  cashierState = "已入賬";
  }
 }
 }

 /// <summary>
 /// 配送員
 /// </summary>
 public class Dilliveryman : JobStation
 {
 private string dillivierymanState;
 private Customer customer;

 public Dilliveryman(Customer customer)
 {
  this.customer = customer;
 }

 public override void Update()
 {
  if (customer.CustomerState == "已付款")
  {
  Console.WriteLine("我是配送員，我來(lái)發(fā)貨。");
  dillivierymanState = "已發(fā)貨";
  }
 }
 }

 class Program
 {
 static void Main(string[] args)
 {

  Customer subject = new Customer();

  subject.Attach(new Accountant(subject));
  subject.Attach(new Cashier(subject));
  subject.Attach(new Dilliveryman(subject));

  subject.CustomerState = "已付款";
  subject.Notify();

  Console.Read();
 }
 }

 /// <summary>
 /// 抽象主題
 /// </summary>
 public interface ISubject
 {
 void Notify();
 }

 /// <summary>
 /// 聲明委托
 /// </summary>
 public delegate void CustomerEventHandler();

 /// <summary>
 /// 具體主題
 /// </summary>
 public class Customer : ISubject
 {
 private string customerState;

 // 聲明一個(gè)委托事件，類型為 CustomerEventHandler
 public event CustomerEventHandler Update;

 public void Notify()
 {
  if (Update != null)
  {
  // 使用事件來(lái)通知給訂閱者
  Update();
  }
 }

 public string CustomerState
 {
  get { return customerState; }
  set { customerState = value; }
 }
 }

 /// <summary>
 /// 財(cái)務(wù)，已經(jīng)不需要實(shí)現(xiàn)抽象的觀察者類，并且不用引用具體的主題
 /// </summary>
 public class Accountant
 {
 private string accountantState;

 public Accountant()
 { }

 /// <summary>
 /// 開發(fā)票
 /// </summary>
 public void GiveInvoice()
 {
  Console.WriteLine("我是會(huì)計(jì)，我來(lái)開具發(fā)票。");
  accountantState = "已開發(fā)票";
 }
 }

 /// <summary>
 /// 出納，已經(jīng)不需要實(shí)現(xiàn)抽象的觀察者類，并且不用引用具體的主題
 /// </summary>
 public class Cashier
 {
 private string cashierState;

 public void Recoded()
 {
  Console.WriteLine("我是出納員，我給登記入賬。");
  cashierState = "已入賬";
 }
 }

 /// <summary>
 /// 配送員，已經(jīng)不需要實(shí)現(xiàn)抽象的觀察者類，并且不用引用具體的主題
 /// </summary>
 public class Dilliveryman
 {
 private string dillivierymanState;

 public void Dilliver()
 {
  Console.WriteLine("我是配送員，我來(lái)發(fā)貨。");
  dillivierymanState = "已發(fā)貨";
 }
 }

 class Program
 {
 static void Main(string[] args)
 {

  Customer subject = new Customer();

  Accountant accountant = new Accountant();
  Cashier cashier = new Cashier();
  Dilliveryman dilliveryman = new Dilliveryman();

  // 注冊(cè)事件
  subject.Update += accountant.GiveInvoice;
  subject.Update += cashier.Recoded;
  subject.Update += dilliveryman.Dilliver;

  /*
  * 以上寫法也可以用下面代碼來(lái)替換
  subject.Update += new CustomerEventHandler(accountant.GiveInvoice);
  subject.Update += new CustomerEventHandler(cashier.Recoded);
  subject.Update += new CustomerEventHandler(dilliveryman.Dilliver);
  */

  subject.CustomerState = "已付款";
  subject.Notify();

  Console.Read();
 }
 }