模式定義

狀態模式(State Pattern) ：允許一個對象在其內部狀態改變時改變它的行為，對象看起來似乎修改了它的類。

UML類圖

• 環境類(Context): 定義一個接口，用以封裝環境對象的一個特定的狀態所對應的行為。
• 抽象狀態類(State)： 每一個具體狀態類都實現了環境的一個狀態所對應的行為。

• 具體狀態類(ConcreteState)：定義客戶端所感興趣的接口，並且保留一個具體狀態類的實例。這個具體狀態類的實例給出此環境對象的現有狀態。

  代碼結構

  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

  那前幾天火的微信小遊戲“頭腦王者”距離吧！

  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 = "入手新門";
      }
  
      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 = "堅韌黑鐵";
      }
      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("用戶：{0}，等級為：{1}",this.Name,this.State.Name);
      }
  }
   
  

狀態模式(State)