行为型设计模式之备忘录模式(Memento)

结构
意图	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这个状态。这样以后就可将该对象恢复到原先保存的状态。
适用性	必须保存一个对象在某一个时刻的(部分)状态, 这样以后需要时它才能恢复到先前的状态。 如果一个用接口来让其它对象直接得到这些状态，将会暴露对象的实现细节并破坏对象

using System;

    class Originator 
    {
        private double manufacturer=0;
        private double distributor = 0;
        private double retailer = 0;

        public void MakeSale(double purchasePrice)
        {
            // We assume sales are divided equally amount the three
            manufacturer += purchasePrice * .40;
            distributor += purchasePrice *.3;
            retailer += purchasePrice *.3;
            // Note: to avoid rounding errors for real money handling 
            // apps, we should be using decimal integers
            // (but hey, this is just a demo!)
        }

        public Memento CreateMemento()
        {
            return (new Memento(manufacturer, distributor, retailer));            
        }
        
        public void SetMemento(Memento m)
        {
            manufacturer = m.A;
            distributor = m.B;
            retailer = m.C;
        }        
    }

    class Memento 
    {
        private double iA;
        private double iB;
        private double iC;

        public Memento(double a, double b, double c)
        {
            iA = a;
            iB = b;
            iC = c;
        }

        public double A 
        {
            get 
            {
                return iA;
            }
        }

        public double B 
        {
            get 
            {
                return iB;
            }
        }

        public double C 
        {
            get 
            {
                return iC;
            }
        }
    }

    class caretaker 
    {
        
    }

        /// <summary>
    ///    Summary description for Client.
    /// </summary>
    public class Client
    {
        public static int Main(string[] args)
        {              
            Originator o = new Originator();
            
            // Assume that during the course of running an application 
            // we we set various data in the originator
            o.MakeSale(45.0);
            o.MakeSale(60.0);

            // Now we wish to record the state of the object
            Memento m = o.CreateMemento();

            // We make further changes to the object
            o.MakeSale(60.0);
            o.MakeSale(10.0);
            o.MakeSale(320.0);

            // Then we decide ot change our minds, and revert to the saved state (and lose the changes since then)
            o.SetMemento(m);

            return 0;
        }
    }