文章中部分内容和思路来自《Head First设计模式》
模式定义
动态地将责任附加到对象上。若要扩展功能，装饰者提供了比继承更有弹性的替代方案
模式类图
典型案例
1.案例说明
去咖啡店喝咖啡，我们可以要求店员在咖啡中加各种调味品，如牛奶、摩卡等。我们可以将这些调味品称为装饰
2.代码实现
------------
IComponent.h
------------
#ifndef ICOMPONENT_H
#define ICOMPONENT_H
class IComponent
{
public:
virtual float cost() = 0;
};
#endif // ICOMPONENT_H
------------
Decoration.h
------------
#ifndef DECORATION_H
#define DECORATION_H
#include "IComponent.h"
class Decoration : public IComponent
{
public:
Decoration();
virtual ~Decoration();
};
#endif // DECORATION_H
--------------
Decoration.cpp
--------------
#include "Decoration.h"
Decoration::Decoration()
{
}
Decoration::~Decoration()
{
}
------------
HouseBlend.h
------------
#ifndef HOUSEBLEND_H
#define HOUSEBLEND_H
#include "IComponent.h"
class HouseBlend : public IComponent
{
public:
HouseBlend();
virtual ~HouseBlend();
public:
virtual float cost();
};
#endif // HOUSEBLEND_H
--------------
HouseBlend.cpp
--------------
#include "HouseBlend.h"
HouseBlend::HouseBlend()
{
}
HouseBlend::~HouseBlend()
{
}
float HouseBlend::cost()
{
return 4.5;
}
----------------
MilkDecoration.h
----------------
#ifndef MILKDECORATION_H
#define MILKDECORATION_H
#include "Decoration.h"
class MilkDecoration : public Decoration
{
public:
MilkDecoration(IComponent *cp);
virtual ~MilkDecoration();
public:
virtual float cost();
private:
IComponent *_cp;
};
#endif // MILKDECORATION_H
------------------
MilkDecoration.cpp
------------------
#include "MilkDecoration.h"
MilkDecoration::MilkDecoration(IComponent *cp)
{
_cp = cp;
}
MilkDecoration::~MilkDecoration()
{
}
float MilkDecoration::cost()
{
return _cp->cost() + 0.3;
}
------
Moka.h
------
#ifndef MOKA_H
#define MOKA_H
#include "Decoration.h"
class Moka : public Decoration
{
public:
Moka(IComponent *cp);
virtual ~Moka();
public:
virtual float cost();
private:
IComponent *_cp;
};
#endif // MOKA_H
--------
Moka.cpp
--------
#include "Moka.h"
Moka::Moka(IComponent *cp)
{
_cp = cp;
}
Moka::~Moka()
{
}
float Moka::cost()
{
return _cp->cost() + 1.6;
}
--------
main.cpp
--------
/**
* 设计模式-装饰者模式
* 要点：1,组件与装饰有共同超类 2,装饰可以装饰到任何组件
*/
#include <QCoreApplication>
#include <QDebug>
#include "MilkDecoration.h"
#include "HouseBlend.h"
#include "Moka.h"
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
HouseBlend *blend = new HouseBlend;
MilkDecoration *deco = new MilkDecoration(blend); // houseblend加牛奶
qDebug() << deco->cost();
Moka *mokaDeco = new Moka(blend); // houseblend加摩卡
qDebug() << mokaDeco->cost();
Moka *mokaDeco2 = new Moka(deco); // houseblend加牛奶加摩卡
qDebug() << mokaDeco2->cost();
delete mokaDeco2;
mokaDeco2 = NULL;
delete mokaDeco;
mokaDeco = NULL;
delete deco;
deco = NULL;
delete blend;
blend = NULL;
return a.exec();
}