05.桥模式.md

桥模式 Bridge

• 使用对象间的组合关系解耦了抽象和实现之间固有的绑定关系，使得抽象和实现可以沿着各自的维度来变化

动机

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

模式定义

将抽象部分（业务功能）与实现部分（平台实现）分离，使它们都可以独立的变化。

代码

原始设计

class Messager{
public:
    virtual void Login(string username, stirng passwaed) = 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 n
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 m
class PCMessagerLite : public PCMessagerBase{
public:
    virtual void Login(string username, stirng passwaed){
        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, stirng passwaed){
        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, stirng passwaed){
        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, stirng passwaed){
        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
    Message* m = new MobileMessagerPerfect();
}

类的规模：1 + n + m*n

重构设计

class Messager{
protected:
    MessagerImp* messagerImp;
public:
    Messager(MessagerImp* Imp) : messagerImp(Imp){}
    virtual void Login(string username, stirng passwaed) = 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 n
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(){
        //...
    }
};

//业务抽象 m
class MessagerLite : public Messager{
public:
    virtual void Login(string username, stirng passwaed){
        messager->Connect();
    }
    virtual void SendMessage(string message){
        messager->WriteText();
    }
    virtual void SendPicture(Image image){
        messager->DrawShape();
    }
};
class MessagerPerfect : public Messager{
public:
    virtual void Login(string username, stirng passwaed){
        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 MessagerLite(mImp);
}

类的规模：1 + n + m

题目

• 桥接模式-万能遥控器