C# 设计模式-备忘录（Menento）

在不破坏封装性的前提下，捕获一个对象的内部状态，并在该对象之外保存该状态。使得该对象可恢复到原先保存的状态。

主要组成：

Menento-备忘录，存储原发器的内部状态。

Originator-原发器，创建备忘录，用于记录内部状态

Caretaker-负责人，负责备忘录的管理

相关类：

using System.Collections.Generic;

namespace Memento
{
    /// <summary>
    /// 备忘录
    /// </summary>
    class Menento
    {
        public string State { get; set; }

        public Menento(string state)
        {
            State = state;
        }
    }

    /// <summary>
    /// 原发器
    /// </summary>
    class Originator
    {
        public string State { get; set; }

        //创建备忘录
        public Menento CreateMenento()
        {
            return new Menento(State);
        }
        //恢复状态
        public void SetMemento(Menento memento)
        {
            State = memento.State;
        }
    }

    /// <summary>
    /// 负责人
    /// </summary>
    class Caretaker
    {
        //编号和相应备忘录
        Dictionary<int, Menento> numberAndMenentos = new Dictionary<int, Menento>();

        public void AddMenentos(int number, Menento menento)
        {
            if (!numberAndMenentos.ContainsKey(number))
            {
                numberAndMenentos.Add(number, menento);
            }
        }

        public Menento GetMenento(int number)
        {
            if (numberAndMenentos.ContainsKey(number))
            {
                return numberAndMenentos[number];
            }
            else
            {
                return null;
            }
        }
    }
}

调用：

using System;

namespace Memento
{
    class Program
    {
        static void Main(string[] args)
        {
            //负责人
            Caretaker caretaker = new Caretaker();

            Originator fileOriginator = new Originator();

            fileOriginator.State = "状态1";
            //创建备忘录
            Menento menento1 = fileOriginator.CreateMenento();
            caretaker.AddMenentos(1, menento1);

            fileOriginator.State = "状态2";
            //创建备忘录
            Menento menento2 = fileOriginator.CreateMenento();
            caretaker.AddMenentos(2, menento2);

            Console.WriteLine("当前状态：{0}", fileOriginator.State);

            //恢复状态
            fileOriginator.SetMemento(caretaker.GetMenento(1));
            Console.WriteLine("恢复到：{0}",fileOriginator.State);

            //恢复状态
            fileOriginator.SetMemento(caretaker.GetMenento(2));
            Console.WriteLine("恢复到：{0}",fileOriginator.State);

            Console.Read();
        }
    }
}

结果：

参考资料：《设计模式-可复用面对对象软件的基础》