/// <summary>
 /// Context類，維護(hù)一個ConcreteState子類的實例，這個實例定義當(dāng)前的狀態(tài)。
 /// </summary>
 public class Context
 {
  private State state;
  /// <summary>
  /// 定義Context的初始狀態(tài)
  /// </summary>
  /// <param name="state"></param>
  public Context(State state)
  {
   this.state = state;
  }

  /// <summary>
  /// 可讀寫的狀態(tài)屬性，用于讀取和設(shè)置新狀態(tài)
  /// </summary>
  public State State
  {
   get { return state; }
   set { state = value; }
  }

  /// <summary>
  /// 對請求做處理，并設(shè)置下一個狀態(tài)
  /// </summary>
  public void Request()
  {
   state.Handle(this);
  }
 }

 /// <summary>
 /// 抽象狀態(tài)類，定義一個接口以封裝與Context的一個特定狀態(tài)相關(guān)的行為
 /// </summary>
 public abstract class State
 {
  public abstract void Handle(Context context);
 }

 /// <summary>
 /// 具體狀態(tài)類，每一個子類實現(xiàn)一個與Context的一個狀態(tài)相關(guān)的行為
 /// </summary>
 public class ConcreteStateA : State
 {
  /// <summary>
  /// 設(shè)置ConcreteStateA的下一個狀態(tài)是ConcreteStateB
  /// </summary>
  /// <param name="context"></param>
  public override void Handle(Context context)
  {
   Console.WriteLine("當(dāng)前狀態(tài)是 A.");
   context.State = new ConcreteStateB();
  }
 }

 public class ConcreteStateB : State
 {
  /// <summary>
  /// 設(shè)置ConcreteStateB的下一個狀態(tài)是ConcreteSateA
  /// </summary>
  /// <param name="context"></param>
  public override void Handle(Context context)
  {
   Console.WriteLine("當(dāng)前狀態(tài)是 B.");
   context.State = new ConcreteStateA();
  }
 }

 class Program
 {
  static void Main(string[] args)
  {
   // 設(shè)置Context的初始狀態(tài)為ConcreteStateA
   Context context = new Context(new ConcreteStateA());

   // 不斷地進(jìn)行請求，同時更改狀態(tài)
   context.Request();
   context.Request();
   context.Request();
   context.Request();

   Console.Read();
  }
 }

 /// <summary>
 /// 電燈類，對應(yīng)模式中的Context類
 /// </summary>
 public class Light
 {
  private LightState state;

  public Light(LightState state)
  {
   this.state = state;
  }

  /// <summary>
  /// 按下電燈開關(guān)
  /// </summary>
  public void PressSwich()
  {
   state.PressSwich(this);
  }

  public LightState State
  {
   get { return state; }
   set { state = value; }
  } 
 }

 /// <summary>
 /// 抽象的電燈狀態(tài)類，相當(dāng)于State類
 /// </summary>
 public abstract class LightState
 {
  public abstract void PressSwich(Light light);
 }

 /// <summary>
 /// 具體狀態(tài)類, 開
 /// </summary>
 public class On : LightState
 {
  /// <summary>
  /// 在開狀態(tài)下，按下開關(guān)則切換到關(guān)的狀態(tài)。
  /// </summary>
  /// <param name="light"></param>
  public override void PressSwich(Light light)
  {
   Console.WriteLine("Turn off the light.");

   light.State = new Off();
  }
 }

 /// <summary>
 /// 具體狀態(tài)類，關(guān)
 /// </summary>
 public class Off: LightState
 {
  /// <summary>
  /// 在關(guān)狀態(tài)下，按下開關(guān)則打開電燈。
  /// </summary>
  /// <param name="light"></param>
  public override void PressSwich(Light light)
  {
   Console.WriteLine("Turn on the light.");

   light.State = new On();
  }
 }

 class Program
 {
  static void Main(string[] args)
  {
   // 初始化電燈，原始狀態(tài)為關(guān)
   Light light = new Light(new Off());

   // 第一次按下開關(guān)，打開電燈
   light.PressSwich();
   // 第二次按下開關(guān)，關(guān)閉電燈
   light.PressSwich();

   Console.Read();
  }
 }