• 动机
  • 由于某种类型的固有的实现逻辑，使得他们具有两个维度的，乃至多个维度的变化

bridge 桥模式

sample

1. 在不同的平台上支持相同的功能
2. 在各自平台上有自己特有的功能

   class Messager{
       public:
           virtual void Login(string username,string password)=0;
           virtual void SendMessage(string message);
           virtual void SendPicture(Image imagae);
   
           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{
               virtual void PlaySound(){
               //======
           }
   
           virtual void DrawShape(){
               //=======
           }
   
           virtual void WriteText(){
               //======
           }
   
           virtual void Connect(){
               //======
           }
   }
   // 业务抽象
   
   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();
               //*******8
           }
   
           virtual void SendPicture(Image image){
               PCMessagerBase::PlaySound();
               //**********
               PCMessagerBase::DrawShape();
           }
   }
   
   class PCmessagerLite : public PCmessager{
       public:
           virtual void Login(string username,string password){
               PCmessager::Connect();
               //.....
           }
   
           virtual void SendMesager(string message){
               PCmessager::WriteText();
               //.....
           }
   
           virtual void SendPicture(Image iamge){
               PCmessager::DrawShape();
               //.....
           }
   }
   
   
   class MobileMessager :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();
           }
   
   class MobileMessagerLite : public MobileMessagerBase{
       public:
           virtual void Login(string username,string password){
               MobileMessagerBase::Connect();
               //.....
           }
   
           virtual void SendMesager(string message){
               MobileMessagerBase.WriteText();
               //.....
           }
   
           virtual void SendPicture(Image iamge){
               MobileMessagerBase.DrawShape();
               //.....
           }
       }
   }
   
   // 编译时装配
   void Process(){
       Messager *m =new MobileMessagerPerfect();
   }

改进

class MessagerImpl{
    public:

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

        virtual ~Messager(){}
};
class Messager{
    protected:
        MessagerImpl* messageimpl;
    public:
        virtual void Login(string username,string password)=0;
        virtual void SendMessage(string message)=0;
        virtual void SendPicture(Image imagae)=0;
        ~MessagerImpl();
}
//平台实现
class PCMessagerImpl : public MessagerImpl{
    public:
        virtual void PlaySound(){
            //******
        }

        virtual void DrawShape(){
            //******
        }

        virtual void WriteText(){
            //******
        }

        virtual void Connect(){
            //******
        }
};

class MobileMessagerImpl:public MessagerImpl{
        virtual void PlaySound(){
            //======
        }

        virtual void DrawShape(){
            //=======
        }

        virtual void WriteText(){
            //======
        }

        virtual void Connect(){
            //======
        }
}
// 业务抽象
// 将继承转换为内部类
class MessagerPerfect :public Messager {
    public:
        virtual void Login(string username,string password){
            messageBase->PlaySound();
            //*********
            messageBase->Connect();
        }

        virtual void SendMessage(string message){

            messageBase->PlaySound();
            //**********
            messageBase->WriteText();
            //*******8
        }

        virtual void SendPicture(Image image){
            messageBase->PlaySound();
            //**********
            messageBase->DrawShape();
        }
        MessagerPerfect(Messager* messager):messageBase(messager){}

}

class MessagerLite : public Messager{
    
    public:
        virtual void Login(string username,string password){
            messageBase->Connect();
            //.....
        }

        virtual void SendMesager(string message){
            messageBase->WriteText();
            //.....
        }

        virtual void SendPicture(Image iamge){
            messageBase->DrawShape();
            //.....
        }
        MessagerLite(Messager* messager):messageBase(messager){}
}


}

// 运行时装配
void Process(){
    MessagerImpl* m =new MessagerLite(new MobileMessagerBase());
    MessagerImpl* m =new MessagerLite(new PCMessagerBase());
}

模式定义

将抽象部分(业务功能)与实现部分(平台实现)分离，是他们可以独立的变化

UML图

要点总结

• Bridge 模式使用 “对象间的组合关系” 接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。所谓抽象和实现沿着各自维度的变化，即“子类化”他们。
• Bridge 模式有时候类似于多继承方案，但是多继承往往违背-单一职责(即一个类只有一个变化的原因)。复用性比较差。Bridge 模式是比多继承方案更好的解决方案
• Bridge 模式的应用一般在 “两个非常强的变化维护” ，有时一个类也有多余两个的变化维度这时可以使用bridge的扩展模式