{C#}设计模式辨析.状态

背景

• 前序状态执行后，切换到后续状态
• 与责任链异同
  • 责任链：遍历并下放到具体责任者处理要求
  • 状态：在不同状态中轮转处理要求

示例

using System;
using static System.Console;

namespace DesignPattern_State
{
    // 游戏类 =上下文类
    public class Game
    {
        public IState CurrentPlayer { get; set; }

        public void Play()
        {
            for (int turn = 0; turn < 10; turn++)
            {
                Write($"#{turn} ");
                CurrentPlayer.Handle(turn == 9);
            }
        }
    }

    // 状态接口
    public interface IState
    {
        IState Opposite { set; get; }
        void Handle(bool won = false);
    }

    // 玩家类 =具体状态
    public class Player : IState
    {
        private readonly Game game;
        private readonly string name;
        private Random random = new Random();

        // 因互相引用，延迟到属性(非构造器)中初始化
        public IState Opposite { set; get; }

        public Player(Game game, string name)
        {
            this.game = game;
            this.name = name;
        }

        public void Handle(bool won = false)
        {
            string seconds = new string('.', random.Next(1, 5));
            Write($"Thinking {seconds}");

            string info = won
                ? $"Player {this} won. Game over."
                : $"Player {this} played. Turn to player {Opposite}.";
            WriteLine(info);

            game.CurrentPlayer = Opposite;
        }

        public override string ToString() => name;
    }

    class Program
    {
        static void Main(string[] args)
        {
            var game = new Game();

            var zhang = new Player(game, "Zhang");
            var li = new Player(game, "Li");
            zhang.Opposite = li;
            li.Opposite = zhang;

            game.CurrentPlayer = zhang;
            game.Play();

            ReadKey();
        }
    }
}