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备忘录模式

概念

备忘录模式（Memento Pattern）是一种行为设计模式，用于在不暴露对象内部状态的情况下，捕获并存储对象的当前状态，以便日后可以将对象恢复到存储的状态。备忘录模式可以有效地实现撤销/恢复操作。

组件和职责

使用场景

优点与缺点

与其他模式的比较

实现代码

C++ 实现

#include <iostream>
#include <string>
#include <vector>

// Memento
class Memento {
private:
    std::string state;

public:
    Memento(const std::string& s) : state(s) {}
    std::string getState() const { return state; }
};

// Originator
class Originator {
private:
    std::string state;

public:
    void setState(const std::string& s) { state = s; }
    std::string getState() const { return state; }

    Memento saveToMemento() { return Memento(state); }
    void restoreFromMemento(const Memento& memento) { state = memento.getState(); }
};

// Caretaker
class Caretaker {
private:
    std::vector<Memento> mementoList;

public:
    void addMemento(const Memento& memento) { mementoList.push_back(memento); }
    Memento getMemento(size_t index) { return mementoList.at(index); }
};

// Example
int main() {
    Originator originator;
    Caretaker caretaker;

    originator.setState("State1");
    caretaker.addMemento(originator.saveToMemento());

    originator.setState("State2");
    caretaker.addMemento(originator.saveToMemento());

    originator.setState("State3");

    std::cout << "Current State: " << originator.getState() << std::endl;

    originator.restoreFromMemento(caretaker.getMemento(0));
    std::cout << "Restored to: " << originator.getState() << std::endl;

    return 0;
}

C# 实现

using System;
using System.Collections.Generic;

// Memento
class Memento {
    public string State { get; private set; }
    public Memento(string state) {
        State = state;
    }
}

// Originator
class Originator {
    public string State { get; set; }

    public Memento SaveToMemento() {
        return new Memento(State);
    }

    public void RestoreFromMemento(Memento memento) {
        State = memento.State;
    }
}

// Caretaker
class Caretaker {
    private List<Memento> _mementos = new List<Memento>();

    public void AddMemento(Memento memento) {
        _mementos.Add(memento);
    }

    public Memento GetMemento(int index) {
        return _mementos[index];
    }
}

// Example
class Program {
    static void Main() {
        Originator originator = new Originator();
        Caretaker caretaker = new Caretaker();

        originator.State = "State1";
        caretaker.AddMemento(originator.SaveToMemento());

        originator.State = "State2";
        caretaker.AddMemento(originator.SaveToMemento());

        originator.State = "State3";

        Console.WriteLine($"Current State: {originator.State}");

        originator.RestoreFromMemento(caretaker.GetMemento(0));
        Console.WriteLine($"Restored to: {originator.State}");
    }
}

类图

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