裝飾模式（Decorator），動態的給一個對象添加一些額外的職責，就增加功能來說，裝飾模式比生成子類更加靈活。
//Decorator.h
#ifndef _DECORATOR_H
#define _DECORATOR_H
#include <string>
/*Component 類定義一個對象接口，可以給這些對象動態的添加指責*/
class Component
{
public:
Component();
virtual ~Component();
virtual void Operation()=0;
};
/*ConcreteComponent是定義了一個具體的對象，也可以給這個對象添加一些職責*/
class ConcreteComponent:public Component
{
public:
ConcreteComponent();
virtual ~ConcreteComponent();
void Operation();
};
/*Decorator,裝飾抽象類，從外類來擴展Component類的功能
但對於Component來說是無需知道Decorator的存在*/
class Decorator:public Component
{
protected:
Component* _com;
public:
Decorator(Component* cpt);
virtual ~Decorator();
void Operation();
};
/*具體的裝飾對象，起到給Component添加職責的功能*/
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()
{
//先執行父類的operation方法，然後在執行本子類特有的功能
//相當於對於原Component進行了裝飾
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;
}