C++设计模式~策略模式(Strategy)

灰太狼 2022-04-03 13:08 262阅读 0赞

### 文章目录 ###

*   *  商城促销的案例
     *  单纯策略模式代码举例
     *   *  strategy.h
         *  strategy.cpp
         *  main.cpp
     *  策略模式+简单工厂模式代码举例
     *   *  strategy.h
         *  strategy.cpp
         *  main.cpp

## 商城促销的案例 ##

> 1.简单工厂模式实现  
> ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0JfTmVtbw_size_16_color_FFFFFF_t_70]![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0JfTmVtbw_size_16_color_FFFFFF_t_70 1]  
> 简单工厂模式我需要让客户端认识两个类，CashSuper和CashFactory

> 2.策略模式+简单工厂模式实现  
> ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0JfTmVtbw_size_16_color_FFFFFF_t_70 2]![在这里插入图片描述][20181222131837275.png]  
> 而策略模式我只需要给客户端暴露CashContext类即可，耦合更加降低了，

## 单纯策略模式代码举例 ##

### strategy.h ###

#ifndef STRATEGY_H
    #define STRATEGY_H
    
    class Strategy
    {
    public:
        Strategy();
        virtual void AlgorithmInterface() = 0;
    };
    
    class ConcreteStrategyA:public Strategy
    {
    public:
        ConcreteStrategyA() {}
        void AlgorithmInterface();
    };
    
    class ConcreteStrategyB:public Strategy
    {
    public:
        ConcreteStrategyB() {}
        void AlgorithmInterface();
    };
    
    class ConcreteStrategyC:public Strategy
    {
    public:
        ConcreteStrategyC() {}
        void AlgorithmInterface();
    };
    
    class Context
    {
    public:
        Context(Strategy *strategy);
        Strategy *strategy;
        void ContextInterface();
    };
    #endif // STRATEGY_H

### strategy.cpp ###

### main.cpp ###

#include <iostream>
    #include "strategy.h"
    
    using namespace std;
    
    int main()
    {
        Context contextA(new ConcreteStrategyA());
        contextA.ContextInterface();
    
        Context contextB(new ConcreteStrategyB());
        contextB.ContextInterface();
    
        Context contextC(new ConcreteStrategyC());
        contextC.ContextInterface();
    
        return 0;
    }

## 策略模式+简单工厂模式代码举例 ##

### strategy.h ###

#ifndef STRATEGY_H
    #define STRATEGY_H
    
    enum AlgorithmMode
    {
        ALGORITHMA,
        ALGORITHMB,
        ALGORITHMC,
    };
    
    
    class Strategy
    {
    public:
        Strategy();
        virtual void AlgorithmInterface() = 0;
    };
    
    class ConcreteStrategyA:public Strategy
    {
    public:
        ConcreteStrategyA() {}
        void AlgorithmInterface();
    };
    
    class ConcreteStrategyB:public Strategy
    {
    public:
        ConcreteStrategyB() {}
        void AlgorithmInterface();
    };
    
    class ConcreteStrategyC:public Strategy
    {
    public:
        ConcreteStrategyC() {}
        void AlgorithmInterface();
    };
    
    class Context
    {
    public:
        Context(Strategy *strategy);//策略模式
        Context(int AlgorithmMode);//策略模式+简单工厂模式
        Strategy *strategy;
        void ContextInterface();
    };
    #endif // STRATEGY_H

### strategy.cpp ###

#include "strategy.h"
    #include <iostream>
    using namespace std;
    
    Strategy::Strategy()
    {
    
    }
    
    void ConcreteStrategyA::AlgorithmInterface()
    {
        cout<<"AlgorithmInterface of ConcreteStrategyA"<<endl;
    }
    
    void ConcreteStrategyB::AlgorithmInterface()
    {
        cout<<"AlgorithmInterface of ConcreteStrategyB"<<endl;
    }
    
    void ConcreteStrategyC::AlgorithmInterface()
    {
        cout<<"AlgorithmInterface of ConcreteStrategyC"<<endl;
    }
    
    
    //策略模式：初始化的时候传入具体的策略对象
    Context::Context(Strategy *strategy)
    {
        this->strategy = strategy;
    }
    
    //简单工厂模式：封装了对象的创建的接口
    Context::Context(int AlgorithmMode)
    {
        switch (AlgorithmMode) {
        case ALGORITHMA:
            this->strategy = new ConcreteStrategyA();
            break;
    
        case ALGORITHMB:
            this->strategy = new ConcreteStrategyB();
            break;
    
        case ALGORITHMC:
            this->strategy = new ConcreteStrategyC();
            break;
    
        default:
            this->strategy = nullptr;
            break;
        }
    }
    
    //再根据具体的策略对象来调用其算法接口
    void Context::ContextInterface()
    {
        this->strategy->AlgorithmInterface();
    }

### main.cpp ###

#include <iostream>
    #include "strategy.h"
    
    using namespace std;
    
    int main()
    {
        /***************策略模式**************/
        Context contextA(new ConcreteStrategyA());
        contextA.ContextInterface();
    
        Context contextB(new ConcreteStrategyB());
        contextB.ContextInterface();
    
        Context contextC(new ConcreteStrategyC());
        contextC.ContextInterface();
    
        /***********策略模式+工厂模式**********/
        Context contextA1(ALGORITHMA);
        contextA1.ContextInterface();
    
        Context contextB1(ALGORITHMB);
        contextB1.ContextInterface();
    
        Context contextC1(ALGORITHMC);
        contextC1.ContextInterface();
    
        return 0;
    }

![在这里插入图片描述][20181222134454345.png]  
上述代码显示策略模式+工厂模式，客户端只要管理一个类：Context即可，调用的ContextInterface(),这样就彻底把算法和客户端分离出来了，耦合度更低

> 策略模式就是用来封装算法的，但在实践中，我们发现可以用来封装几乎任何类型的规则，只要在分析的过程中听到：需要在不同的时间对应不同的业务规则，就可以考虑用策略模式处理这种变化的可能性，但是在基本的策略模式中，选择所用的具体实现的职责由客户端对象承担，并转给策略模式的Context对象，这本身并没有解除客户端需要判断的压力，而策略模式+简单工厂模式后，选择具体实现的职责可以由Context来承担，这样就最大化的减轻了客户端的职责

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[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0JfTmVtbw_size_16_color_FFFFFF_t_70 1]: /images/20220403/d86165c8dbb74a69bbfc53f405e0d6b8.png
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[20181222131837275.png]: /images/20220403/763ff7f51be04bfa9705129409fa002d.png
[20181222134454345.png]: /images/20220403/70a7464324f342c998859cdd2cd317d7.png