浅谈设计模式之八——Decorator模式

先上uml图：

意图：动态地给一个对象添加一些额外的职责。就增加功能来说，Decorator模式相比生成子类更为灵活。
uml解析：装饰者模式又名包装器，顾名思义就是给某个对象添加一些功能，而不是给整个类添加一些功能。Component跟Decorator是聚合关系，子类ConcreteDecoratorA和ConcreteDecoratorB实现具体对Component的修饰。
下面给出可执行的示例代码：
Decorator.h

#pragma once#include <iostream>using namespace std;class Component{public:    Component(void);    virtual ~Component(void);    virtual void Operation()=0;};class ConcreteComponent:public Component{public:    void Operation();};class Decorator:public Component{public:    Decorator(Component *component):m_Component(component){}    void Operation();protected:    Component *m_Component;};class ConcreteDecoratorA:public Decorator{public:    ConcreteDecoratorA(Component *component):Decorator(component){}    void Operation();    void AddState();};class ConcreteDecoratorB:public Decorator{public:    ConcreteDecoratorB(Component *component):Decorator(component){}    void Operation();    void AddBehavior();};

Decorator.cpp

#include "Component.h"Component::Component(void){}Component::~Component(void){}void ConcreteComponent::Operation(){    cout<<"ConcreteComponent"<<endl;}void Decorator::Operation(){    m_Component->Operation();};void ConcreteDecoratorA::AddState(){    cout<<"AddState"<<endl;}void ConcreteDecoratorA::Operation(){    AddState();    m_Component->Operation();}void ConcreteDecoratorB::AddBehavior(){    cout<<"AddBehavior"<<endl;}void ConcreteDecoratorB::Operation(){    AddBehavior();    m_Component->Operation();}

main.cpp

#include "Component.h"int main(int argc,char **argv){    //未装饰    Component *p1=new ConcreteComponent;    p1->Operation();    //DecoratorA    Component *p2=new ConcreteDecoratorA(p1);    p2->Operation();    //DecoratorB    Component *p3=new ConcreteDecoratorB(p1);    p3->Operation();    return 0;}

执行结果：

可看到分别对ConcreteComponent的装饰。