状态模式

来看一下状态模式的角色组成吧：
1) 使用环境（Context）角色：客户程序是通过它来满足自己的需求。它定义了客户程序需要的接口；并且维护一个具体状态角色的实例，这个实例来决定当前的状态。
2) 状态（State）角色：定义一个接口以封装与使用环境角色的一个特定状态相关的行为。
3) 具体状态（Concrete State）角色：实现状态角色定义的接口

下面是GOF在《设计模式》中给出的状态模式的适用情况：
1) 一个对象的行为取决于它的状态, 并且它必须在运行时刻根据状态改变它的行为。
2) 一个操作中含有庞大的多分支的条件语句，且这些分支依赖于该对象的状态

 

using System;
using System.Collections.Generic;
using System.Text;
using System.Collections;

namespace StatePatten
...{
    class Program
    ...{
        static void Main(string[] args)
        ...{
            TcpConnection tcpcon = new TcpConnection();
            tcpcon.Open();
            tcpcon.Acknowledge();
            tcpcon.Open();
            tcpcon.Close();
            tcpcon.Acknowledge();
            tcpcon.Close();
        }
    }

    public interface ITcpState
    ...{
        void Open();
        void Close();
        void Acknowledge();
    }

    public class TcpConnection
    ...{
        private ITcpState state;

        public ITcpState State
        ...{
            set ...{ state = value; }
        }

        public void Open()
        ...{
            this.state = new TcpEstablished();
            this.state.Open();
            this.state = new TcpListen();
        }

        public void Close()
        ...{
            this.state.Close();
            this.state = new TcpClosed();
        }

        public void Acknowledge()
        ...{
            this.state.Acknowledge();
        }
    }

    public class TcpEstablished : ITcpState
    ...{
        public void Open()
        ...{
            Console.WriteLine("Have opened, can not open again!");
        }

        public void Close()
        ...{
            Console.WriteLine("Closing");
        }

        public void Acknowledge()
        ...{
            Console.WriteLine("TcpEstablished!");
        }
    }

    public class TcpListen : ITcpState
    ...{
        public void Open()
        ...{
            Console.WriteLine("Have opened, can not open again!");
        }

        public void Close()
        ...{
            Console.WriteLine("Closing");
        }

        public void Acknowledge()
        ...{
            Console.WriteLine("Tcp Listen!");
        }
    }

    public class TcpClosed : ITcpState
    ...{
        public void Open()
        ...{
            Console.WriteLine("Opening");
        }

        public void Close()
        ...{
            Console.WriteLine("Have closed, can't close again!");
        }

        public void Acknowledge()
        ...{
            Console.WriteLine("Tcp Closed!");
        }
    }
}