设计模式（六）bridge

1.使用场景：某些类具有两个或多个变化的维度（平台），且不同维度中有大量重复的静态特质代码

2.理论依据：多态、虚函数

3.定义：将抽象部分（业务功能）与实现部分（平台实现）分离，使得他们都可以独立地变化

4.步骤：将原基类，拆分为两个或多个不同的基类，新的基类通过组合实现它们之间的关系，通过对新基类，进行类似decorator设计模式的操作，完成对不同维度责任的划分

5.技法：继承->组合
编译时装配->运行时装配（多态）

6.变化：原基类根据不同维度（平台）拆分，通过多态实现运行时调用的功能
不变：不能再改变的基类

对比decorator：

相同点：对于A类要调用B类的功能，并且A类的成员函数的实现，都是直接或间接通过调用B类的成员函数，此时

使用组合的设计方式

不同点：bridge还需根据不同的平台对基类进行拆分，组合使用是在拆分的基类中完成的
而decorator并不需要拆分

原代码：

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(){}};//平台实现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(){        //==========    }};//业务抽象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();        //........    }};void Process(){        //编译时装配        Messager *m =            new MobileMessagerPerfect();}

使用bridge设计模式：

class Messager{protected:     MessagerImp* messagerImp;//...public:    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(){}};//平台实现 nclass 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(){        //==========    }};//业务抽象 m//类的数目：1+n+mclass MessagerLite :public Messager {    public:        virtual void Login(string username, string password){                messagerImp->Connect();        //........    }    virtual void SendMessage(string message){                messagerImp->WriteText();        //........    }    virtual void SendPicture(Image image){                messagerImp->DrawShape();        //........    }};class MessagerPerfect  :public Messager {       public:        virtual void Login(string username, string password){                messagerImp->PlaySound();        //********        messagerImp->Connect();        //........    }    virtual void SendMessage(string message){                messagerImp->PlaySound();        //********        messagerImp->WriteText();        //........    }    virtual void SendPicture(Image image){                messagerImp->PlaySound();        //********        messagerImp->DrawShape();        //........    }};void Process(){    //运行时装配    MessagerImp* mImp=new PCMessagerImp();    Messager *m =new Messager(mImp);}