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   1: // 訂閱者

   2: public interface iObserver

   3: {

   4:     void Update();

   5: }

   6: // 主題

   7: public interface iSubject

   8: {

   9:     void Add(iObserver observer);    // 加入一個訂閱者

  10:     void Delete(iObserver observer); // 刪除一個訂閱者

  11:     void Notify();                   // 通知訂閱者 

  12: }

   1: public class Subject : iSubject

   2:     {

   3:         private bool m_sent;             // 判斷是否已經通知觀察者

   4:         public string infomation         // 設定/取得 主題

   5:         {

   6:             get;

   7:             set;

   8:         }

   9:         // 紀錄觀察者

  10:         List<iObserver> m_observers = new List<iObserver>();

  11:         // 實作Add

  12:         public void Add(iObserver observer)

  13:         {

  14:             m_observers.Add(observer);

  15:             if (m_observers.Count >= 1)

  16:             {

  17:                 m_sent = true;

  18:             }

  19:             else

  20:             {

  21:                 m_sent = false;

  22:             }

  23:         }

  24:         // 實作Delete

  25:         public void Delete(iObserver observer)

  26:         {

  27:             m_observers.Remove(observer);

  28:             if( m_observers.Count >=1)

  29:             {

  30:                 m_sent = true;

  31:             }

  32:             else

  33:             {

  34:                 m_sent = false;

  35:             }

  36:         }

  37:         // 實作Notify

  38:         public void Notify()

  39:         {

  40:             if (m_sent)

  41:             {

  42:                 foreach (iObserver o in m_observers)

  43:                 {

  44:                     o.Update();

  45:                 }

  46:                 m_sent = false;

  47:             }

  48:         }

  49:     }

   1: // 訂閱者

   2:     public class Subsriber : iObserver

   3:     {

   4:         private string m_username;      // 訂閱者名稱

   5:         private string m_infomation;    // 訂閱者端接收主題

   6:         private Subject m_Subject;      // 主題  

   7:         // 建構子(傳入主題和訂閱者名稱)

   8:         public Subsriber(Subject subject, string username)

   9:         {

  10:             m_Subject = subject;      

  11:             m_username = username;

  12:         }

  13:         // 訂閱某個主題

  14:         public Subject subscibe

  15:         {

  16:             get { return m_Subject; }

  17:             set { m_Subject = value; }

  18:         }

  19:         // 實作Update

  20:         public void Update()

  21:         {

  22:             m_infomation = m_Subject.infomation;

  23:             MessageBox.Show(string.Format("觀察者{0}, 收到資訊{1}", m_username, m_infomation));

  24:         }

  25:     }

   1: // 主題

   2: Subject s = new Subject();

   3: // 三個訂閱者

   4: Subsriber user1, user2, user3;

   5:  

   6: // (1)實體化三個訂閱者, 傳入主題和使用者名稱, 並訂閱主題

   7: user1 = new Subsriber(s, "user #1"); 

   8: s.Add(user1);

   9:  

  10: user2 = new Subsriber(s, "user #2");  

  11: s.Add(user2);

  12:  

  13: user3 = new Subsriber(s, "user #3");

  14: s.Add(user3);

  15:  

  16: // 設定主題名稱並通知訂閱者

  17: s.infomation = "Hello World";

  18: s.Notify();

   1: // (2)主題刪除訂閱者2

   2:  s.Delete(user2);

   3: s.infomation = "user #2 is deleted";

   4: s.Notify();

   1: // (3)訂閱者刪除訂閱主題

   2: user3.subscibe.Delete(user3);

   3: s.infomation = "Now notify user1 only";

   4: s.Notify();