《大话设计模式》学习笔记14：备忘录模式

游戏进度备忘示例：

1.Originator：

    public class GameRole
    {
        public int Vitality { get; set; }
        public int Attack { get; set; }
        public int Defense { get; set; }
        //状态显示
        public void StateDisplay()
        {
            Console.WriteLine("角色当前状态：体力 {0}，攻击力 {1}，防御力 {2}", Vitality, Attack, Defense);
        }
        //获得初始状态
        public void GetInitState()
        {
            Vitality = 100;
            Attack = 100;
            Defense = 100;
        }
        //战斗
        public void Fight()
        {
            Vitality = 0;
            Attack = 0;
            Defense = 0;
        }

        public RoleStateMemento SaveState()
        {
            return new RoleStateMemento(Vitality, Attack, Defense);
        }
        public void RecoveryState(RoleStateMemento roleStateMemento)
        {
            Vitality = roleStateMemento.Vitality;
            Attack = roleStateMemento.Attack;
            Defense = roleStateMemento.Defense;
        }
    }

2.Memento：

    public class RoleStateMemento
    {
        public int Vitality { get; set; }
        public int Attack { get; set; }
        public int Defense { get; set; }

        public RoleStateMemento(int vitality,int attack,int defense)
        {
            Vitality = vitality;
            Attack = attack;
            Defense = defense;
        }
    }

3.Caretaker：

    public class RoleStateCaretaker
    {
        public RoleStateMemento RoleStateMemento { get; set; }

    }

4.客户端代码：

    class Program
    {
        static void Main(string[] args)
        {
            GameRole gameRole = new GameRole();
            gameRole.GetInitState();
            gameRole.StateDisplay();

            RoleStateCaretaker roleStateCaretaker = new RoleStateCaretaker();
            roleStateCaretaker.RoleStateMemento = gameRole.SaveState();

            gameRole.Fight();
            gameRole.StateDisplay();

            gameRole.RecoveryState(roleStateCaretaker.RoleStateMemento);
            gameRole.StateDisplay();
        }
    }

　　备忘录模式比较适用于功能比较复杂的，但需要维护或记录属性历史的类，或者需要保存的属性只是众多属性中的一小部分时，Originator可以根据保存的Memento信息还原到前一状态。

　　如果某个系统中使用命令模式时，需要实现命令的撤销功能，那么命令模式可以使用备忘录模式来存储可撤销操作的状态。