作用:
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為靈活。
UML結構圖:
抽象基類:
1)Component:定義一個對象接口,可以為這個接口動態的添加職責.
2)Decorator:維持一個指向Component的指針,并且有一個和Component一致的接口函數.
接口函數:
1)Component::Operation:這個接口函數由Component聲明,因此Component的派生類都需要實現,可以在這個接口函數的基礎上給它動態添加職責.
解析:
Decorator的派生類可以為ConcreateComponent類的對象動態的添加職責,或者可以這么說:Decorator的派生類裝飾ConcreateComponent類的對象.具體是這么實現的,首先初始化一個ConcreateComponent類的對象(被裝飾者),采用這個對象去生成一個Decorator對象(裝飾者),之后對Operation函數的調用則是對這個Decorator對象成員函數的多態調用.這里的實現要點是Decorator類和ConcreateComponent類都繼承自Component,從而兩者的接口函數是一致的;其次,Decorator維護了一個指向Component的指針,從而可以實現對Component::Operation函數的動態調用.
實現:
1)Decorator.h
/**//********************************************************************
????created:????2006/07/20
????filename:?????Decorator.h
????author:????????李創
????????????????http://www.shnenglu.com/converse/
????purpose:????Decorator模式的演示代碼
*********************************************************************/
#ifndef?DECORATOR_H
#define?DECORATOR_H
//?抽象基類,定義一個對象接口,可以為這個接口動態的添加職責.
class?Component
{
public:
????Component(){}
????virtual?~Component(){}
????//?純虛函數,由派生類實現
????virtual?void?Operation()?=?0;
};
//?抽象基類,維護一個指向Component對象的指針
class?Decorator
????:?public?Component
{
public:
????Decorator(Component*?pComponent)?:?m_pComponent(pComponent){}
????virtual?~Decorator();
protected:
????Component*?m_pComponent;
};
//?派生自Component,在這里表示需要給它動態添加職責的類
class?ConcreateComponent
????:?public?Component
{
public:
????ConcreateComponent(){}
????virtual?~ConcreateComponent(){}
????virtual?void?Operation();
};
//?派生自Decorator,這里代表為ConcreateComponent動態添加職責的類
class?ConcreateDecorator
????:?public?Decorator
{
public:
????ConcreateDecorator(Component*?pComponent)?:?Decorator(pComponent){}
????virtual?~ConcreateDecorator(){}
????virtual?void?Operation();
private:
????void?AddedBehavior();
};
#endif2)Decorator.cpp
/**//********************************************************************
????created:????2006/07/20
????filename:?????Decorator.cpp
????author:????????李創
????????????????http://www.shnenglu.com/converse/
????purpose:????Decorator模式的演示代碼
*********************************************************************/
#include?"Decorator.h"
#include?<iostream>
Decorator::~Decorator()
{
????delete?m_pComponent;
????m_pComponent?=?NULL;
}
void?ConcreateComponent::Operation()
{
????std::cout?<<?"Operation?of?ConcreateComponent\n";
}
void?ConcreateDecorator::Operation()
{
????m_pComponent->Operation();
????AddedBehavior();
}
void?ConcreateDecorator::AddedBehavior()
{
????std::cout?<<?"AddedBehavior?of?ConcreateDecorator\n";
} 3)Main.cpp
/**//********************************************************************
????created:????2006/07/20
????filename:?????Main.cpp
????author:????????李創
????????????????http://www.shnenglu.com/converse/
????purpose:????Decorator模式的測試代碼
*********************************************************************/
#include?"Decorator.h"
#include?<stdlib.h>
int?main()
{
????//?初始化一個Component對象
????Component*?pComponent?=?new?ConcreateComponent();
????//?采用這個Component對象去初始化一個Decorator對象,
????//?這樣就可以為這個Component對象動態添加職責
????Decorator*?pDecorator?=?new?ConcreateDecorator(pComponent);
????pDecorator->Operation();
????delete?pDecorator;
????system("pause");
????return?0;
}