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): 在环境类中维护一个抽象状态类型State的字段，一调用状态的处理行为和状态切换业务逻辑。
• 抽象状态类(State)：用于定义一个接口以封装与环境类的一个特定状态相关的行为。
• 具体状态类(ConcreteState)：是抽象状态类的子类，实现特定状态的行为，每一个子类实现一个与环境类的一个状态相关的行为。

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

有一款比较火的微信小游戏“头脑王者”，不同的等级，需要不同的”星“才可以晋级

	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);
		}
	}