淺談設計模式之八——Decorator模式

先上uml圖：

意圖：動態地給一個對象添加一些額外的職責。就增加功能來說，Decorator模式相比生成子類更爲靈活。
uml解析：裝飾者模式又名包裝器，顧名思義就是給某個對象添加一些功能，而不是給整個類添加一些功能。Component跟Decorator是聚合關係，子類ConcreteDecoratorA和ConcreteDecoratorB實現具體對Component的修飾。
下面給出可執行的示例代碼：
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)
{
    //未裝飾
    Component *p1=new ConcreteComponent;
    p1->Operation();
    //DecoratorA
    Component *p2=new ConcreteDecoratorA(p1);
    p2->Operation();
    //DecoratorB
    Component *p3=new ConcreteDecoratorB(p1);
    p3->Operation();
    return 0;
}

執行結果：

可看到分別對ConcreteComponent的裝飾。