《C++设计模式》——行为型

前言

行为型模式是对在不同的对象之间划分责任和算法的抽象化。行为型模式不仅仅关注类和对象的结构，而且重点关注它们之间的相互作用。

Interpreter(解释器)

Template Method(模板方法)

GOOD：把不变的代码部分都转移到父类中，将可变的代码用 virtual 留到子类重写。

template.h

#ifndef CLION_TEST_TEMPLATE_H
#define CLION_TEST_TEMPLATE_H

#include <iostream>

using namespace std;

// 金庸小说考题试卷
class TestPaper {
public:
    void TestQuestion1() {
        cout << "杨过得到，后来给了郭静，炼成倚天剑、屠龙刀的玄铁可能是[] a.球磨铸铁 b.马口铁 c.高速合金钢 d.碳素纤维"
             << endl;
        cout << "答案：" << Answer1() << endl;
    }

    void TestQuestion2() {
        cout << "杨过、程英、陆无双铲除了情花，造成[] a.使这种植物不再害人 b.使一种珍稀物种灭绝 c.破坏了那个生物圈的生态平衡 d.造成该地区沙漠化"
             << endl;
        cout << "答案：" << Answer2() << endl;
    }

    void TestQuestion3() {
        cout << "蓝凤凰致使华山师徒、桃谷六仙呕吐不止，如果你是大夫，会给他们开什么药[] a.阿司匹林 b.牛黄解毒片 c.氟哌酸 d.让他们喝大量的生牛奶 e.以上全部对"
             << endl;
        cout << "答案：" << Answer3() << endl;
    }

protected:
    virtual char Answer1() = 0;

    virtual char Answer2() = 0;

    virtual char Answer3() = 0;
};


class TestPaperA : public TestPaper {
    char Answer1() final {
        return 'b';
    }

    char Answer2() final {
        return 'c';
    }

    char Answer3() final {
        return 'a';
    }
};

class TestPaperB : public TestPaper {
    char Answer1() final {
        return 'c';
    }

    char Answer2() final {
        return 'a';
    }

    char Answer3() final {
        return 'a';
    }
};

#endif //CLION_TEST_TEMPLATE_H

main.cpp

#include "template.h"

using namespace std;

int main() {
    system("chcp 65001");
    // 模板方法
    cout<<"学生甲抄的试卷："<<endl;
    TestPaper* studentA = new TestPaperA();
    studentA->TestQuestion1();
    studentA->TestQuestion2();
    studentA->TestQuestion3();
    
    cout<<"学生乙抄的试卷："<<endl;
    TestPaper* studentB = new TestPaperB();
    studentB->TestQuestion1();
    studentB->TestQuestion2();
    studentB->TestQuestion3();
    return 0;
}

Chain of Responsibility(责任链)

Command(命令)

Iterator(迭代器)

Mediator(中介者)

Memento(备忘录)

Observer(观察者)

GOOD：定义了一种一对多的关系，让多个观察对象（公司员工）同时监听一个主题对象（秘书），主题对象状态发生变化时，会通知所有的观察者，使它们能够更新自己。

observer.h

#ifndef CLION_TEST_OBSERVER_H
#define CLION_TEST_OBSERVER_H

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

using namespace std;

class SecretaryBase;

// 抽象观察者
class CObserverBase {
protected:
    string name;
    SecretaryBase *sub;
public:
    CObserverBase(string strname, SecretaryBase *strsub) {
        name = strname;
        sub = strsub;
    }

    virtual void Update() = 0;
};

// 具体的观察者，看股票的
class StockObserver : public CObserverBase {
public:
    StockObserver(string strname, SecretaryBase *strsub) : CObserverBase(strname, strsub) {

    }

    virtual void Update();
};

// 具体的观察者，看NBA的
class NBAObserver : public CObserverBase {
public:
    NBAObserver(string strname, SecretaryBase *strsub) : CObserverBase(strname, strsub) {}

    virtual void Update();
};

// 抽象通知者
class SecretaryBase {
public:
    string action;
    vector<CObserverBase *> observers;
public:
    virtual void Attach(CObserverBase *observer) = 0;

    virtual void Notify() = 0;
};

// 具体通知者
class Secretary : public SecretaryBase {
public:
    void Attach(CObserverBase *ob) {
        observers.emplace_back(ob);
    }

    void Notify() {
        for (CObserverBase *observer: observers) {
            observer->Update();
        }
    }
};

void StockObserver::Update() {
    cout << name << ":" << sub->action << ",不要玩股票了，要开始工作了" << endl;
}

void NBAObserver::Update() {
    cout << name << ":" << sub->action << ",不要看NBA了，老板来了" << endl;
}


#endif //CLION_TEST_OBSERVER_H

main.cpp

#include "observer.h"

using namespace std;

int main() {
    system("chcp 65001");
    // 观察者模式
    SecretaryBase *p = new Secretary(); // 创建观察者

    // 被观察者的对象
    CObserverBase *s1 = new NBAObserver("小李", p);
    CObserverBase *s2 = new StockObserver("小赵", p);
    // 加入观察队列
    p->Attach(s1);
    p->Attach(s2);
    // 事件
    p->action = "老板来了";
    // 通知
    p->Notify();

    return 0;
}

State(状态)

GOOD：当一个对象的行为取决于它的状态，并且它必须在运行时刻根据状态改变它的行为时，可考虑用到状态模式。

state.h

#ifndef CLION_TEST_STATE_H
#define CLION_TEST_STATE_H

#include<iostream>

using namespace std;

class State;

class ForenoonState;

class NoonState;

class AfternonnState;

class EveningState;

class SleepingState;

class RestState;

class Work;

// 抽象状态角色，负责定义各个状态有哪些行为，该抽象状态包含所有具体状态的方法。并且封装环境角色，帮助切换状态。
class State {
public:
    virtual ~State() = default;

    virtual void writeprogram(Work *w) = 0;
};

// Context 角色，在该类内部维护一个ConcreteState子类的一个实例，可以负责具体状态的切换
// 工作
class Work {
private:
    State *current;
    double m_hour;
    bool m_finish;
public:
    Work();

    ~Work();

    void setHour(double hour) { m_hour = hour; }

    double getHour() const { return m_hour; }

    void setFinish(bool finish) { m_finish = finish; }

    bool getFinish() const { return m_finish; }

    void SetState(State *s) {
        delete current;
        current = s;
    }

    void WorkProgram() {
        current->writeprogram(this);
    }
};

// 下面都是具体的状态类，每一个具体状态类必须完成两个职责：该类本状态下要做的事情，以及如何执行到其他具体状态类的状态。
// 上午工作状态
class ForenoonState : public State {
public:
    void writeprogram(Work *w) final;
};

// 中午工作状态
class NoonState : public State {
public:
    void writeprogram(Work *w) final;
};

// 下午工作状态
class AfternoonState : public State {
public:
    void writeprogram(Work *w) final;
};

// 晚些工作状态
class EveningState : public State {
public:
    void writeprogram(Work *w) final;
};

// 睡眠状态
class SleepingState : public State {
public:
    void writeprogram(Work *w) final;

};

//下午休息状态
class RestState : public State {// 下班休息状态
public:
    void writeprogram(Work *w) final;

};

Work::Work() {
    current = new ForenoonState();
}

Work::~Work() {
    delete current;
}

void ForenoonState::writeprogram(Work *w) {
    if (w->getHour() < 12) {
        cout << "当前时间：" << w->getHour() << "点，上午工作，精神百倍" << endl;
    } else {
        w->SetState(new NoonState());
        w->WorkProgram();
    }
}

void NoonState::writeprogram(Work *w) {
    if (w->getHour() < 13) {
        cout << "当前时间：" << w->getHour() << "点，吃午饭，睡午觉" << endl;
    } else {
        w->SetState(new AfternoonState());
        w->WorkProgram();
    }
}

void AfternoonState::writeprogram(Work *w) {
    if (w->getHour() < 17) {
        cout << "当前时间：" << w->getHour() << "点，下午状态还不错" << endl;
    } else {
        w->SetState(new EveningState());
        w->WorkProgram();
    }
}

void EveningState::writeprogram(Work *w) {
    if (w->getFinish()) {
        w->SetState(new RestState());
        w->WorkProgram();
    } else {
        if (w->getHour() < 21) {
            cout << "当前时间：" << w->getHour() << "点,加班哦，疲惫至极 " << endl;
        } else {
            w->SetState(new SleepingState());
            w->WorkProgram();
        }
    }
}

void SleepingState::writeprogram(Work *w) {
    cout << "当前时间：" << w->getHour() << "点,不行了，睡着了 " << endl;
}

void RestState::writeprogram(Work *w) {
    cout << "当前时间：" << w->getHour() << "点,下班回家了 " << endl;
}

#endif //CLION_TEST_STATE_H

main.cpp

#include <iostream>
#include "state.h"

using namespace std;

int main()
{
    system("chcp 65001");
    // 紧急项目
    Work emergencyProjects;

    emergencyProjects.setHour(9);
    emergencyProjects.WorkProgram();

    emergencyProjects.setHour(10);
    emergencyProjects.WorkProgram();

    emergencyProjects.setHour(12);
    emergencyProjects.WorkProgram();

    emergencyProjects.setHour(13);
    emergencyProjects.WorkProgram();

    emergencyProjects.setHour(14);
    emergencyProjects.WorkProgram();

    emergencyProjects.setHour(17);
    emergencyProjects.WorkProgram();

    emergencyProjects.setFinish(false);

    emergencyProjects.setHour(19);
    emergencyProjects.WorkProgram();

    emergencyProjects.setHour(22);
    emergencyProjects.WorkProgram();

    system("pause");
    return 0;
}

Strategy(策略)

定义算法家族，分别封装起来，让它们之间可以互相替换，让算法变化，不会影响到用户
GOOD：适合类中的成员以方法为主，算法经常变动；简化了单元测试（因为每个算法都有自己的类，可以通过自己的接口单独测试。
策略模式和简单工厂基本相同，但简单工厂模式只能解决对象创建问题，对于经常变动的算法（方法）应使用策略模式。
BUG：客户端要做出判断。

strategy.h

#ifndef CLION_TEST_STRATEGY_H
#define CLION_TEST_STRATEGY_H

// 策略基类
class COperation {
public:
    int m_nFirst;
    int m_nSecond;

    virtual double GetResult() {
        double dResult = 0;
        return dResult;
    }
};

// 策略具体类——加法类
class AddOperation : public COperation {
public:
    AddOperation() {

    }
    AddOperation(int a, int b) {
        m_nFirst = a;
        m_nSecond = b;
    }

    double GetResult() final {
        return m_nFirst + m_nSecond;
    }
};

class Context {
private:
    COperation *op;
public:
    Context(COperation *temp) {
        op = temp;
    }

    double GetResult() {
        return op->GetResult();
    }
};

#endif //CLION_TEST_STRATEGY_H

main.h

#include <iostream>
#include "strategy.h"

using namespace std;

int main() {
    system("chcp 65001");
    // 简单工厂模式
    int a = 1;
    int b = 2;
    // 策略模式
    char c = '+';
    switch (c) {
        case '+':
            Context* context = new Context(new AddOperation(a,b));
            cout<<context->GetResult()<<endl;
            break;
        default:
        break;
    }
    return 0;
}

策略模式与工厂结合

将实例化具体的类过程移至到Context对象的引用中。
strategy.h

  // 策略与工厂结合
  Context(char cType) {
      switch(cType) {
          case '+': op = new AddOperation(3,8);
              break;
          default:
              op = new AddOperation();
              break;
      }
  }

main.h

int main()
{
	int a,b;
	cin>>a>>b;
	Context *test=new Context('+');
	cout<<test­>GetResult()<<endl;
	return 0;
}

Visitor(访问者)

后记