状态模式(State)

模式定义

状态模式(State Pattern) ：允许一个对象在其内部状态改变时改变它的行为，对象看起来似乎修改了它的类。

UML类图

• 环境类(Context): 定义一个接口，用以封装环境对象的一个特定的状态所对应的行为。
• 抽象状态类(State)： 每一个具体状态类都实现了环境的一个状态所对应的行为。

• 具体状态类(ConcreteState)：定义客户端所感兴趣的接口，并且保留一个具体状态类的实例。这个具体状态类的实例给出此环境对象的现有状态。

  代码结构

  public class StateApp
  {
      public void Run()
      {
          Context c = new Context(new ConcreteStateA());
  
          c.Request();
          c.Request();
          c.Request();
  
          Console.ReadKey();
      }
  }
  
  abstract class State
  {
      public abstract void Handle(Context context);
  }
  
  class ConcreteStateA : State
  {
      public override void Handle(Context context)
      {
          context.State = new ConcreteStateB();
      }
  }
  
  class ConcreteStateB : State
  {
      public override void Handle(Context context)
      {
          context.State = new ConcreteStateA();
      }
  }
  
  class Context
  {
      public State State { get; set; }
  
      public Context(State state)
      {
          this.State = state;
      }
      public void Request()
      {
          this.State.Handle(this);
      }
  }

  情景案例

  那前几天火的微信小游戏“头脑王者”距离吧！

  public class StateRealWorldApp
  {
      public void Run()
      {
          Player player = new Player("小王");
          player.Display();
  
          for (int i = 0; i < 5; i++)
          {
              player.Win();
          }
          player.Display();
  
          Console.ReadKey();
      }
  }
  
  abstract class Grade
  {
      protected int Score = 0;
      public string Name = string.Empty;
      public Player Player { get; set; }
      public abstract void Win();
      public abstract void Lose();
  }
  
  class New : Grade
  {
      public New(Player player)
      {
          this.Player = player;
          this.Name = "入手新门";
      }
  
      public override void Win()
      {
          this.Score = this.Score + 1;
          if(this.Score == 5)
          {
              this.Player.State = new Skilled(this);
              this.Score = 0;
          }
      }
  
      public override void Lose()
      {
          if(this.Score != 0)
          {
              this.Score = this.Score - 1;
          }
      }
  }
  
  class Skilled : Grade
  {
      public Skilled(Grade state) 
      {
          this.Player = state.Player;
          this.Name = "起步熟手";
      }
      public override void Win()
      {
          this.Score = this.Score + 1;
          if (this.Score == 7)
          {
              this.Player.State = new BlackIron(this);
              this.Score = 0;
          }
      }
  
      public override void Lose()
      {
          if (this.Score != 0)
          {
              this.Score = this.Score - 1;
          }
      }
  }
  
  class BlackIron : Grade
  {
      public BlackIron(Grade state)
      {
          this.Player = state.Player;
          this.Name = "坚韧黑铁";
      }
      public override void Win()
      {
          this.Score = this.Score + 1;
          if (this.Score == 7)
          {
              this.Score = 0;
          }
      }
  
      public override void Lose()
      {
          if (this.Score != 0)
          {
              this.Score = this.Score - 1;
          }
      }
  }
  
  class Player
  {
      public Grade State { get; set; }
  
      private string Name;
  
      public Player(string name)
      {
          this.State = new New(this);
          this.Name = name;
      }
  
      public void Win()
      {
          this.State.Win();
      }
  
      public void Lose()
      {
          this.State.Lose();
      }
  
      public void Display()
      {
          Console.WriteLine("用户：{0}，等级为：{1}",this.Name,this.State.Name);
      }
  }