以下笔记摘录自李建忠老师的<<c++设计模式>>和书籍<<设计模式>>

动机

  • 由于某些类型的固有的实现逻辑，使得它们具有两个变化的维度，乃至多个纬度的变化。

定义

  • 将抽象部分(业务功能)与实现部分(平台兼容)分离，使他们都可以独立的变化。

原始代码

抽象类
平台实现
业务抽象
使用
  • 抽象类中包含了两个维度的接口
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    class Messager{
    public:
        virtual void Login(string username, string password)=0;
        virtual void SendMessage(string message)=0;
        virtual void SendPicture(Image image)=0;

        virtual void PlaySound()=0;
        virtual void DrawShape()=0;
        virtual void WriteText()=0;
        virtual void Connect()=0;

        virtual ~Messager(){}
    };
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class PCMessagerBase : public Messager{
public:

    virtual void PlaySound(){
        //**********
    }
    virtual void DrawShape(){
        //**********
    }
    virtual void WriteText(){
        //**********
    }
    virtual void Connect(){
        //**********
    }
};

class MobileMessagerBase : public Messager{
public:

    virtual void PlaySound(){
        //==========
    }
    virtual void DrawShape(){
        //==========
    }
    virtual void WriteText(){
        //==========
    }
    virtual void Connect(){
        //==========
    }
};
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class PCMessagerLite : public PCMessagerBase {
public:

    virtual void Login(string username, string password){

        PCMessagerBase::Connect();
        //........
    }
    virtual void SendMessage(string message){

        PCMessagerBase::WriteText();
        //........
    }
    virtual void SendPicture(Image image){

        PCMessagerBase::DrawShape();
        //........
    }
};

class PCMessagerPerfect : public PCMessagerBase {
public:

    virtual void Login(string username, string password){

        PCMessagerBase::PlaySound();
        //********
        PCMessagerBase::Connect();
        //........
    }
    virtual void SendMessage(string message){

        PCMessagerBase::PlaySound();
        //********
        PCMessagerBase::WriteText();
        //........
    }
    virtual void SendPicture(Image image){

        PCMessagerBase::PlaySound();
        //********
        PCMessagerBase::DrawShape();
        //........
    }
};

class MobileMessagerLite : public MobileMessagerBase {
public:

    virtual void Login(string username, string password){

        MobileMessagerBase::Connect();
        //........
    }
    virtual void SendMessage(string message){

        MobileMessagerBase::WriteText();
        //........
    }
    virtual void SendPicture(Image image){

        MobileMessagerBase::DrawShape();
        //........
    }
};

class MobileMessagerPerfect : public MobileMessagerBase {
public:

    virtual void Login(string username, string password){

        MobileMessagerBase::PlaySound();
        //********
        MobileMessagerBase::Connect();
        //........
    }
    virtual void SendMessage(string message){

        MobileMessagerBase::PlaySound();
        //********
        MobileMessagerBase::WriteText();
        //........
    }
    virtual void SendPicture(Image image){

        MobileMessagerBase::PlaySound();
        //********
        MobileMessagerBase::DrawShape();
        //........
    }
};

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void Process(){
    //编译时装配
    Messager *m = new MobileMessagerPerfect();
}

重构代码

抽象类拆分并组合
平台实现
业务抽象
使用
  • 抽象类中包含了两个维度的接口
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    class Messager{
    protected:
        MessagerImp * messageImp;
    public:
        Messager(MessagerImp *imp) : messageImp(imp) {}
        virtual void Login(string username, string password)=0;
        virtual void SendMessage(string message)=0;
        virtual void SendPicture(Image image)=0;

        virtual ~Messager(){}
    };
    class MessagerImp{
    public:
        virtual void PlaySound()=0;
        virtual void DrawShape()=0;
        virtual void WriteText()=0;
        virtual void Connect()=0;

        virtual ~MessagerImp(){}
    };
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class PCMessagerImp : public MessagerImp{
public:
    virtual void PlaySound(){
        //**********
    }
    virtual void DrawShape(){
        //**********
    }
    virtual void WriteText(){
        //**********
    }
    virtual void Connect(){
        //**********
    }
};

class MobileMessagerImp : public MessagerImp{
public:
    virtual void PlaySound(){
        //==========
    }
    virtual void DrawShape(){
        //==========
    }
    virtual void WriteText(){
        //==========
    }
    virtual void Connect(){
        //==========
    }
};
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class MessagerLite : public Messager {
public:
    MessagerLite(MessagerImp* mImp) : Messager(mImp) {}
    virtual void Login(string username, string password){
        messageImp->Connect();
        //........
    }
    virtual void SendMessage(string message){
        messageImp->CWriteText();
        //........
    }
    virtual void SendPicture(Image image){
        messageImp->CDrawShape();
        //........
    }
};

class MessagerPerfect : public Messager {
public:
    MessagerPerfect(MessagerImp* mImp) : Messager(mImp) {}
    virtual void Login(string username, string password){
        messageImp->CPlaySound();
        //********
        messageImp->CConnect();
        //........
    }
    virtual void SendMessage(string message){
        messageImp->CPlaySound();
        //********
        messageImp->CWriteText();
        //........
    }
    virtual void SendPicture(Image image){
        messageImp->CPlaySound();
        //********
        messageImp->CDrawShape();
        //........
    }
};
  • 这里也可以通过抽象工厂自动完成Imp的实现
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    void Process(){
        //运行时装配
        MessagerImp* mImp=new PCMessagerImp();
        MessagerLite *mp =new MessagerLite(mImp);
        MessagerPerfect *ml =new MessagerPerfect(mImp);
    }

总结

  • 结构图
许可协议

本文采用 署名-非商业性使用-相同方式共享 4.0 国际 许可协议，转载请注明出处。

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