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至保存时的状态。

2、  模型

角色：

Originator(发起者)——创建备忘录Memorandum，并且根据需要决定，需要保存那些状态。

Memorandum(备忘录)——负责存储Originator对象的内部状态，并防止Originator以外的对象访问这个备忘录。

Caretaker(管理者)——负责保存备忘录。

程序模型：

//发起者，需要保存状态的对象

public class Originator      {          private string stateString1;            public string StateString1          {              get { return stateString1; }                set { stateString1 = value; }          }            private string stateString2;            public string StateString2          {              get { return stateString2; }                set { stateString2 = value; }          }              public Memorandum CreateMemorandum()          {              return new Memorandum(stateString1, stateString2);          }            public void SetMemorandum(Memorandum memorandum)          {              StateString1 = memorandum.StateString1;                StateString2 = memorandum.StateString2;          }            public void ShowMemorandum()          {              Console.WriteLine("当前状态：");                Console.WriteLine("StateString1={0}", stateString1, stateString2);                Console.WriteLine("StateString2={0}", stateString1, stateString2);          }      }

// 存储Originator，其中包括的参数和要存的Originator参数一致

public class Memorandum      {          private string stateString1;            private string stateString2;            public Memorandum(string state1, string state2)          {              this.stateString1 = state1;                this.stateString2 = state2;          }            public string StateString1          {              get { return stateString1; }          }            public string StateString2          {              get { return stateString2; }          }      }

管理者：

public class CareTaker      {          private Memorandum memorandum;            public Memorandum MemorandumClass          {              get { return memorandum; }                set { memorandum = value; }          }        }

调用：

static void Main(string[] args)          {              //发起者参数状态初始化              Originator originator = new Originator();                originator.StateString1 = "参数StateString1——初始化1";                originator.StateString2 = "参数StateString2——初始化1";                originator.ShowMemorandum();                //保存一份备份              CareTaker careTaker = new CareTaker();                careTaker.MemorandumClass = originator.CreateMemorandum();                //发起者参数状态改变了              originator.StateString1 = "参数StateString1——初始化2";                originator.StateString2 = "参数StateString2——初始化2";                originator.ShowMemorandum();                //读取保存的进度              originator.SetMemorandum(careTaker.MemorandumClass);                originator.ShowMemorandum();                Console.ReadKey();          }

结果：

    备忘录模式，实际就是将一个类的当前状态保存一份放着，当状态改变以后，后面需要的时候再去读取保存的状态。而怎么去保存呢，Memorandum承担了保存参数的状态。如果一个类没有行为，而只有属性的话，那么Memorandum就可以写成和发起者一样的类型，保存的时候就可以保存发起者的实例。