设计模式之桥接模式

本文主要是介绍设计模式之桥接模式 - 202201，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

模式动机

设想如果要绘制矩形、圆形、椭圆、正方形，我们至少需要4个形状类，但是如果绘制的图形需要具有不同的颜色，如红色、绿色、蓝色等，此时至少有如下两种设计方案：

第一种设计方案是为每一种形状都提供一套各种颜色的版本。
第二种设计方案是根据实际需要对形状和颜色进行组合

对于有两个变化维度（即两个变化的原因）的系统，采用方案二来进行设计系统中类的个数更少，且系统扩展更为方便。设计方案二即是桥接模式的应用。桥接模式将继承关系转换为关联关系，从而降低了类与类之间的耦合，减少了代码编写量。

模式定义

桥接模式(Bridge Pattern)：将抽象部分与它的实现部分分离，使它们都可以独立地变化。它是一种对象结构型模式，又称为柄体(Handle and Body)模式或接口(Interface)模式。

模式结构

桥接模式包含如下角色：

Abstraction：抽象类
RefinedAbstraction：扩充抽象类
Implementor：实现类接口
ConcreteImplementor：具体实现类

时序图

代码-裸指针版本

// BradgePattern.h
//
// Created by zhaoyf on 2022/4/16.
//#ifndef CPPDESIGNPATTERN_BRIDGEPATTERN_H
#define CPPDESIGNPATTERN_BRIDGEPATTERN_Hnamespace BridgePattern {// Implementorclass Implementor {public:virtual ~Implementor() {}virtual void Action() = 0;};// ConcreteImplementorAclass ConcreteImplementorA : public Implementor {public:virtual ~ConcreteImplementorA() {}virtual void Action();};// ConcreteImplementorBclass ConcreteImplementorB : public Implementor {public:virtual ~ConcreteImplementorB() {}virtual void Action();};// Abstraction, 抽象class Abstraction {public:virtual ~Abstraction() {}virtual void operation() = 0;};// RefinedAbstractionclass RefinedAbstraction : public Abstraction {public:RefinedAbstraction(Implementor *p);virtual ~RefinedAbstraction();virtual void operation() override;private:Implementor *pImpl;};
}#endif //CPPDESIGNPATTERN_BRIDGEPATTERN_H

// BradgePattern.cpp
//
// Created by zhaoyf on 2022/4/16.
//#include "BridgePattern.h"
#include "iostream"namespace BridgePattern {// ConcreteImplementorAvoid ConcreteImplementorA::Action() {std::cout << "ConcreteImplementorA::Action" << std::endl;}// ConcreteImplementorBvoid ConcreteImplementorB::Action() {std::cout << "ConcreteImplementorB::Action" << std::endl;}// RefinedAbstractionRefinedAbstraction::RefinedAbstraction(Implementor *p) : pImpl(p) {}RefinedAbstraction::~RefinedAbstraction() {if (pImpl) {delete pImpl;pImpl = nullptr;}}void RefinedAbstraction::operation() {pImpl->Action();}
}

// main.cpp 测试代码int main() {Implementor *pImplA = new ConcreteImplementorA();Abstraction *pa = new RefinedAbstraction(pImplA);pa->operation();Implementor *pImplB = new ConcreteImplementorB();Abstraction *pb = new RefinedAbstraction(pImplB);pb->operation();delete pa;delete pb;return 0;}output:
ConcreteImplementorA::Action
ConcreteImplementorB::Action

代码-智能指针版本

// BridgePatternSharedPtr.h
//
// Created by zhaoyf on 2022/4/16.
//#ifndef CPPDESIGNPATTERN_BRIDGEPATTERN_SHAREDPTR_H
#define CPPDESIGNPATTERN_BRIDGEPATTERN_SHAREDPTR_H#include <memory>namespace BridgePatternSharedPtr {// Implementorclass Implementor {public:virtual ~Implementor() {}virtual void Action() = 0;};// ConcreteImplementorAclass ConcreteImplementorA : public Implementor {public:virtual ~ConcreteImplementorA() {}virtual void Action();};// ConcreteImplementorBclass ConcreteImplementorB : public Implementor {public:virtual ~ConcreteImplementorB() {}virtual void Action();};// Abstraction, 抽象class Abstraction {public:virtual ~Abstraction() {}virtual void operation() = 0;};// RefinedAbstractionclass RefinedAbstraction : public Abstraction {public:RefinedAbstraction(std::unique_ptr<Implementor> p);virtual ~RefinedAbstraction() {}virtual void operation() override;private:std::unique_ptr<Implementor> pImpl;};}#endif //CPPDESIGNPATTERN_BRIDGEPATTERN_SHAREDPTR_H

// BridgePatternSharedPtr.cpp
//
// Created by zhaoyf on 2022/4/16.
//#include "BridgePattern_SharedPtr.h"
#include "iostream"namespace BridgePatternSharedPtr {// ConcreteImplementorAvoid ConcreteImplementorA::Action() {std::cout << "ConcreteImplementorA::Action" << std::endl;}// ConcreteImplementorBvoid ConcreteImplementorB::Action() {std::cout << "ConcreteImplementorB::Action" << std::endl;}// RefinedAbstractionRefinedAbstraction::RefinedAbstraction(std::unique_ptr<Implementor> p) : pImpl(std::move(p)) {}void RefinedAbstraction::operation() {pImpl->Action();}
}

// main.cpp 测试代码int main() {auto pImplA = std::make_unique<ConcreteImplementorA>();auto pa = std::make_unique<RefinedAbstraction>(std::move(pImplA));pa->operation();auto pb = std::make_unique<RefinedAbstraction>(std::make_unique<ConcreteImplementorB>());pb->operation();return 0;}output:
ConcreteImplementorA::Action
ConcreteImplementorB::Action