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

  1 using System;
  2 
  3     class Originator 
  4     {
  5         private double manufacturer=0;
  6         private double distributor = 0;
  7         private double retailer = 0;
  8 
  9         public void MakeSale(double purchasePrice)
 10         {
 11             // We assume sales are divided equally amount the three
 12             manufacturer += purchasePrice * .40;
 13             distributor += purchasePrice *.3;
 14             retailer += purchasePrice *.3;
 15             // Note: to avoid rounding errors for real money handling 
 16             // apps, we should be using decimal integers
 17             // (but hey, this is just a demo!)
 18         }
 19 
 20         public Memento CreateMemento()
 21         {
 22             return (new Memento(manufacturer, distributor, retailer));            
 23         }
 24         
 25         public void SetMemento(Memento m)
 26         {
 27             manufacturer = m.A;
 28             distributor = m.B;
 29             retailer = m.C;
 30         }        
 31     }
 32 
 33     class Memento 
 34     {
 35         private double iA;
 36         private double iB;
 37         private double iC;
 38 
 39         public Memento(double a, double b, double c)
 40         {
 41             iA = a;
 42             iB = b;
 43             iC = c;
 44         }
 45 
 46         public double A 
 47         {
 48             get 
 49             {
 50                 return iA;
 51             }
 52         }
 53 
 54         public double B 
 55         {
 56             get 
 57             {
 58                 return iB;
 59             }
 60         }
 61 
 62         public double C 
 63         {
 64             get 
 65             {
 66                 return iC;
 67             }
 68         }
 69     }
 70 
 71     class caretaker 
 72     {
 73         
 74     }
 75 
 76         /// <summary>
 77     ///    Summary description for Client.
 78     /// </summary>
 79     public class Client
 80     {
 81         public static int Main(string[] args)
 82         {              
 83             Originator o = new Originator();
 84             
 85             // Assume that during the course of running an application 
 86             // we we set various data in the originator
 87             o.MakeSale(45.0);
 88             o.MakeSale(60.0);
 89 
 90             // Now we wish to record the state of the object
 91             Memento m = o.CreateMemento();
 92 
 93             // We make further changes to the object
 94             o.MakeSale(60.0);
 95             o.MakeSale(10.0);
 96             o.MakeSale(320.0);
 97 
 98             // Then we decide ot change our minds, and revert to the saved state (and lose the changes since then)
 99             o.SetMemento(m);
100 
101             return 0;
102         }
103     }