c++ 行为型模式_备忘录(Memento)

1) 意图

在不破坏封装性的前提下，捕获一个对象的内部状态，并在对象之外保存这个状态。这样可以将对象恢复到原先保存的状态

2) 结构

 

 其中

1. Memento (备忘录)存储Originator内部状态
2. Originator(原发器)创建一个Memento，用于记录当前时刻它的内部状态
3. Caretaker (管理者)负责保存好备忘录，但不能操作或检查备忘录的内容

3) 适用性

1. 必须保存一个对象在某一个时刻的状态，以便需要时恢复此前状态
2. 如果提供一个接口让其他对象得到这些状态，将会暴露对象的实现细节并破坏对象的封装性

4) 举例

 1 #include <iostream>
 2 typedef std::string STATE;
 3 class Originator;
 4 class Memento
 5 {
 6 public:
 7     virtual ~Memento() {}
 8 private:
 9     friend Originator;
10     Memento(STATE& state):m_state(state){}
11     void setState(STATE& state)
12     {
13         m_state = state;
14     }
15     STATE getState()
16     {
17         return m_state;
18     }
19     STATE m_state;
20 };
21 class Originator
22 {
23 public:
24     Originator(STATE& state) :m_state(state) {}
25     virtual ~Originator() {}
26     void setState(std::string& state)
27     {
28         m_state = state;
29     }
30     void setMemento(Memento* pMememnto)
31     {
32         m_state = pMememnto->getState();
33     }
34     Memento* createMemento()
35     {
36         return new Memento(m_state);
37     }
38     void print()
39     {
40         std::cout << " Memento : " << m_state.c_str() << std::endl;
41     }
42 private:
43     STATE m_state;
44 };
45 class Caretaker
46 {
47 public:
48     Caretaker():m_pMemnto(NULL) {}
49     virtual ~Caretaker() {}
50     void setMemento(Memento* p_Memento)
51          {
52             m_pMemnto = p_Memento;
53          }
54     Memento* getCountMemento()
55          {
56              return m_pMemnto;
57          }
58 private:
59     Memento* m_pMemnto;
60 };
61 
62 int main() 
63 {
64     Caretaker* pCaretaker = new Caretaker();
65     
66     Originator* pOriginator = new Originator(std::string("hello"));
67     pOriginator->print();// 显示当前状态
68     Memento* pMemnto = pOriginator->createMemento();
69     pCaretaker->setMemento(pMemnto);//保存备忘录
70     pOriginator->setState(std::string("world"));//修改状态
71     pOriginator->print();// 显示修改后的状态
72 
73     //通过备忘录恢复初始状态
74     pOriginator->setMemento(pCaretaker->getCountMemento());
75     pOriginator->print();
76 
77     delete pCaretaker;
78     delete pOriginator;
79     delete pMemnto;
80     system("pause");
81 }