《设计模式的艺术》笔记 - 备忘录模式-Toy模板网

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介绍

备忘录模式在不破坏封装的前提下，捕获一个对象的内部状态，并在该对象之外保存这个状态，这样可以在以后将对象恢复到原先保存的状态。它是一种对象行为模式，别名为Token。

实现

myclass.h

//
// Created by yuwp on 2024/1/12.
//

#ifndef DESIGNPATTERNS_MYCLASS_H
#define DESIGNPATTERNS_MYCLASS_H

#include <iostream>
#include <unordered_map>
#include <atomic>
#include <vector>
#include <memory>

class Originator;
class Memento { // 备忘录类
    friend Originator;  // 备忘录只能由Originator创建，确保安全
private:
    Memento();
    Memento(Originator *o);
    void setState(const std::string &state);
    std::string &getState();
private:
    std::string m_state;
};

class Originator {  // 原发器类，需要保存状态
public:
    Originator();

    std::shared_ptr<Memento> createMemento();

    void restoreMemento(const std::shared_ptr<Memento> &m);

    void setState(const std::string &state);

    std::string &getState();

private:
    std::string m_state;
};

class Caretaker {   // 负责人类，管理备忘录
public:
    std::shared_ptr<Memento> &getMemento();
    void setMemento(std::shared_ptr<Memento> m);

private:
    std::shared_ptr<Memento> m_memento;
};

#endif //DESIGNPATTERNS_MYCLASS_H

myclass.cpp

//
// Created by yuwp on 2024/1/12.
//

#include "myclass.h"
#include <thread>
#include <unistd.h>
#include <sstream>

Memento::Memento(Originator *o) {
    m_state = o->getState();
}

void Memento::setState(const std::string &state) {
    m_state = state;
}

std::string& Memento::getState() {
    return m_state;
}

Originator::Originator() {

}

std::shared_ptr<Memento> Originator::createMemento() {
    std::shared_ptr<Memento> m(new Memento(this));
    return m;
}

void Originator::restoreMemento(const std::shared_ptr<Memento> &m) {
    setState(m->getState());
}

void Originator::setState(const std::string &state) {
    m_state = state;
}

std::string& Originator::getState() {
    return m_state;
}

void Caretaker::setMemento(std::shared_ptr<Memento> m) {
    m_memento = m;
}

std::shared_ptr<Memento>& Caretaker::getMemento() {
    return m_memento;
}

main.cpp

#include <iostream>
#include <mutex>
#include "myclass.h"

int main() {
    Originator *originator = new Originator();
    originator->setState("初始状态");
    auto m0 = originator->createMemento();
    originator->setState("第一次状态");
    auto m1 = originator->createMemento();
    originator->setState("第二次状态");
    auto m2 = originator->createMemento();
    Caretaker *caretaker = new Caretaker();

    std::cout << "恢复状态前:" << std::endl;
    std::cout << "\t" << originator->getState() << std::endl;

    std::cout << "第一次恢复:" << std::endl;
    caretaker->setMemento(m2);
    originator->restoreMemento(caretaker->getMemento());
    std::cout << "\t" << originator->getState() << std::endl;

    std::cout << "第二次恢复:" << std::endl;
    caretaker->setMemento(m1);
    originator->restoreMemento(caretaker->getMemento());
    std::cout << "\t" << originator->getState() << std::endl;

    std::cout << "第三次恢复:" << std::endl;
    caretaker->setMemento(m0);
    originator->restoreMemento(caretaker->getMemento());
    std::cout << "\t" << originator->getState() << std::endl;

    delete originator;
    delete caretaker;

    return 0;
}