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=;
         private double distributor = ;
         private double retailer = ;

         public void MakeSale(double purchasePrice)
         {
             // We assume sales are divided equally amount the three
             manufacturer += purchasePrice * .;
             distributor += purchasePrice *.;
             retailer += purchasePrice *.;
             // 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 ;
         }
     }

备忘录模式