设计模式之十四:备忘录模式（Memento）

备忘录模式：
在不破换封装性的前提下，捕获一个对象的内部状态并将这个状态保存到对象外部，这样这个对象之后可以恢复到保存的状态。
Without violating encapsulation, capture and externalize an object’s internal state so that the object can be restored to this state later

UML图：

主要包括：

1. Memento（Memento）：存储Originator的内部状态。并可防止Originator以外的其他对象访问备忘录Memento。
2. Originator(SalesProspect)：创建一个包含当前状态快照的备忘录Memento，并可以使用Memento来恢复之前保存的状态。
3. Caretaker(ProspectMemory)：负责保存好备忘录Memento。

这个设计模式很简单，就是面向对象封装这个特性的具体使用。

C++代码：

#include <iostream>#include <string>using namespace std;class Memento{        public:        Memento(string s)        {            state=s;            }        string getState()        {            return state;        }        private:                string state;};class Originator{        public:                void setMemento(Memento *m)                {                    state=m->getState();                }                Memento * createMemento(){                    return new Memento(state);                }                void setState(string s)                {                    state=s;                }                string getState()                {                    return state;                }        private:                string state;};class Caretaker{    public:            Memento* getMemento()            {                return memento;            }            void setMemento(Memento *m)            {                memento=m;            }    private:            Memento * memento;};int main(){    Originator * originator=new Originator();    originator->setState("origin state");    std::cout<<"state 1:"<<originator->getState()<<std::endl;    Caretaker * caretaker=new Caretaker();    caretaker->setMemento(originator->createMemento());    originator->setState("change to state");    std::cout<<"state 2:"<<originator->getState()<<std::endl;    originator->setMemento(caretaker->getMemento());    std::cout<<"state 3:"<<originator->getState()<<std::endl;    return 0;}

执行输出：

下面是一个以具体的例子。

1. Originator为SalesProspect，即代理经销商，他有姓名，号码，经费这些属性
2. Memento为Memento，为保存经销商属性的备忘录
3. Caretaker为ProspectMemory，即保存经销商备忘录的类

UML类图：

C++代码如下：

#include <string>#include <iostream>using namespace std;class Memento{        public:                Memento(string n,string p,double b)                {                    name=n;                    phone=p;                    budget=b;                }                string getName()                {                    return name;                }                string getPhone()                {                    return phone;                }                double getBudget()                {                    return budget;                }        private:                string name;                string phone;                double budget;};class SalesProspect{        public:                void setName(string n)                {                    name=n;                }                void setPhone(string p)                {                    phone=p;                }                void setBudget(double b)                {                    budget=b;                }                string getName()                {                    return name;                }                string getPhone()                {                    return phone;                }                double getBudget()                {                    return budget;                }                Memento* saveMemento()                {                    return new Memento(name,phone,budget);                }                void restoreMemento(Memento * m)                {                    name=m->getName();                    phone=m->getPhone();                    budget=m->getBudget();                }        private:                string name;                string phone;                double budget;};class ProspectMemory{        public:            Memento * getMemento()            {                return memento;            }            void setMemento(Memento * m)            {                memento=m;            }        private:            Memento * memento;};int main(){    SalesProspect * sale=new SalesProspect();    sale->setName("John");    sale->setPhone("15245869785");    sale->setBudget(1200);    std::cout<<"base sale:"<<std::endl<<sale->getName()<<std::endl<<sale->getPhone()<<std::endl<<sale->getBudget()<<std::endl<<std::endl;    ProspectMemory * prospect=new ProspectMemory();    prospect->setMemento(sale->saveMemento());    sale->setName("Mike");    sale->setPhone("13685478523");    sale->setBudget(1500);    std::cout<<"change sale:"<<std::endl<<sale->getName()<<std::endl<<sale->getPhone()<<std::endl<<sale->getBudget()<<std::endl<<std::endl;    sale->restoreMemento(prospect->getMemento());    std::cout<<"restore sale:"<<std::endl<<sale->getName()<<std::endl<<sale->getPhone()<<std::endl<<sale->getBudget()<<std::endl<<std::endl;    delete sale;    delete prospect;    return 0;}

执行输出：