C++状态模式详解：应用场景、与策略模式的区别及代码实现

namespace State_DesignPattern
 {
   using System;

   // 1. 抽象状态类：定义所有具体状态的公共接口
   abstract  class State 
   {
     protected  string strStatename;    

     abstract  public  void Pour();
     // do something state-specific here 
   } 
 
   // 2. 具体状态类：处理特定状态下的请求
   class OpenedState : State 
   {    
     public OpenedState ()
     {
      strStatename =  " Opened " ;
    } 
     override  public  void Pour()
     {
      Console.WriteLine( " pouring " );
      Console.WriteLine( " pouring " );
      Console.WriteLine( " pouring " );
    } 
  } 
  
   class ClosedState : State 
   {    
     public ClosedState()
     {
      strStatename =  " Closed " ;
    } 
     override  public  void Pour()
     {
      Console.WriteLine( " ERROR - bottle is closed - cannot pour " );
    } 
  } 
 
   // 3. 环境类：维护当前状态引用，定义客户感兴趣的接口
   class ContextColaBottle 
   {
     public  enum BottleStateSetting {
      Closed,
      Opened
    } ;

     // 创建具体的状态对象实例
     OpenedState openedState =  new OpenedState();
    ClosedState closedState =  new ClosedState();

     public ContextColaBottle ()
       {
       // 初始化为关闭状态
       CurrentState = closedState;
    } 
 
     private State CurrentState;
    
     // 设置新的状态
     public  void SetState(BottleStateSetting newState)
     {
       if (newState == BottleStateSetting.Closed)
       {
        CurrentState = closedState;
      } 
       else 
       {
        CurrentState = openedState;
      } 
    } 
 
     // 委托给当前状态处理
     public  void Pour()
     {
      CurrentState.Pour();
    }   
  } 
 
   ///  <summary> 
   ///   Summary description for Client.
   ///  </summary> 
   public  class Client
   {
     public  static  int Main( string [] args)
     {
      ContextColaBottle contextColaBottle =  new ContextColaBottle();

      Console.WriteLine( " initial state is closed " );

      Console.WriteLine( " Now trying to pour " );
       contextColaBottle.Pour();

      Console.WriteLine( " Open bottle " );
      contextColaBottle.SetState(ContextColaBottle.BottleStateSetting.Opened);

      Console.WriteLine( " Try to pour again " );
       contextColaBottle.Pour();

       return  0 ;
    } 
  }
}