三、装饰模式

最新推荐文章于 2024-12-24 19:43:09 发布

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本文详细介绍了装饰模式的概念及其在软件设计中的应用。通过示例代码解释了如何动态地为对象添加新的职责，同时保持原有功能不变。展示了装饰模式相比于继承的优势，并提供了具体的实现案例。

装饰模式（Decorator），动态的给一个对象添加一些额外的职责，就增加功能来说，装饰模式比生成子类更加灵活。

//Decorator.h
#ifndef _DECORATOR_H
#define _DECORATOR_H
#include <string>
/*Component 类定义一个对象接口，可以给这些对象动态的添加指责*/
class Component
{
public:
	Component();
	virtual ~Component();
	virtual void Operation()=0;

};
/*ConcreteComponent是定义了一个具体的对象，也可以给这个对象添加一些职责*/
class ConcreteComponent:public Component
{
public:
	ConcreteComponent();
	virtual ~ConcreteComponent();
	void Operation();
};
/*Decorator,装饰抽象类，从外类来扩展Component类的功能
但对于Component来说是无需知道Decorator的存在*/
class Decorator:public Component
{
protected:
	Component* _com;
public:
	Decorator(Component* cpt);
	virtual ~Decorator();
	void Operation();

};
/*具体的装饰对象，起到给Component添加职责的功能*/
class ConcreteDecoratorA:public Decorator
{
public:
	std::string addState;
	ConcreteDecoratorA(Component* cpt);
	~ConcreteDecoratorA();
	void Operation();
};
class ConcreteDecoratorB:public Decorator
{
public:
	ConcreteDecoratorB(Component* cpt);
	~ConcreteDecoratorB();
	void Operation();
	void AddedBehavior();
};
#endif

//Decorator.cpp
#include "Decorator.h"
#include <iostream>
using namespace std;

Component::Component()
{

}
Component::~Component()
{

}
void Component::Operation()
{

}

ConcreteComponent::ConcreteComponent()
{

}
ConcreteComponent::~ConcreteComponent()
{

}
void ConcreteComponent::Operation()
{
	cout<<"ConcreteComponent Operation"<<endl;
}
Decorator::Decorator(Component* cpt)
{
	_com = cpt;
}
Decorator::~Decorator()
{
	if (!_com)
	{
		delete _com;
	}
}

void Decorator::Operation()
{
	_com->Operation();
}
ConcreteDecoratorA::ConcreteDecoratorA(Component* cpt):Decorator(cpt)
{
}
ConcreteDecoratorA::~ConcreteDecoratorA()
{

}
void ConcreteDecoratorA::Operation()
{
	//先执行父类的operation方法，然后在执行本子类特有的功能
	//相当于对于原Component进行了装饰
	Decorator::Operation();
	addState = "New state";
	cout<<addState<<endl;
}
ConcreteDecoratorB::ConcreteDecoratorB(Component* cpt):Decorator(cpt)
{

}
ConcreteDecoratorB::~ConcreteDecoratorB()
{

}
void ConcreteDecoratorB::Operation()
{
	Decorator::Operation();
	AddedBehavior();
}
void ConcreteDecoratorB::AddedBehavior()
{
	cout<<"Added behavior from ConcreteDecoratorB"<<endl;
}

//main.cpp
#include <iostream>
#include "Decorator.h"

int main()
{
	Component* cpt = new ConcreteComponent();
	ConcreteDecoratorA* da = new ConcreteDecoratorA(cpt);
	ConcreteDecoratorB* db = new ConcreteDecoratorB(da);
	db->Operation();

	return 0;
}