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。