常见设计模式的解析和实现(C++)之十三-FlyWeight模式

作用:
运用共享技术有效地支持大量细粒度的对象。

UML结构图:



解析:
Flyweight模式在大量使用一些可以被共享的对象的时候经常使用.比如,在QQ聊天的时候很多时候你懒得回复又不得不回复的时候,一般会用一些客套的话语敷衍别人,如"呵呵","好的"等等之类的,这些简单的答复其实每个人都是提前定义好的,在使用的时候才调用出来.Flyweight就是基于解决这种问题的思路而产生的,当需要一个可以在其它地方共享使用的对象的时候,先去查询是否已经存在了同样的对象,如果没有就生成之有的话就直接使用.因此,Flyweight模式和Factory模式也经常混用.

实现:
需要说明的是下面的实现仅仅实现了对可共享对象的使用,非可共享对象的使用没有列出,因为这个不是Flyweight模式的重点.这里的实现要点是采用一个list链表来保存这些可以被共享的对象,需要使用的时候就到链表中查询是不是已经存在了,如果不存在就初始化一个,然后返回这个对象的指针.

1)Flyweight.h

/********************************************************************    created:    2006/07/26    filename:     FlyWeight.h    author:        李创                http://www.cppblog.com/converse/    purpose:    FlyWeight模式的演示代码*********************************************************************/#ifndef FLYWEIGHT_H#define FLYWEIGHT_H#include <string>#include <list>typedef std::string STATE;class Flyweight{public:    virtual ~Flyweight(){}    STATE GetIntrinsicState();    virtual void Operation(STATE& ExtrinsicState) = 0;protected:    Flyweight(const STATE& state)         :m_State(state)    {    }private:    STATE m_State;};class FlyweightFactory{public:    FlyweightFactory(){}    ~FlyweightFactory();    Flyweight* GetFlyweight(const STATE& key);private:    std::list<Flyweight*>    m_listFlyweight;};class ConcreateFlyweight    : public Flyweight{public:    ConcreateFlyweight(const STATE& state)        : Flyweight(state)    {    }    virtual ~ConcreateFlyweight(){}    virtual void Operation(STATE& ExtrinsicState);};#endif

2)Flyweight.cpp

/********************************************************************    created:    2006/07/26    filename:     FlyWeight.cpp    author:        李创                http://www.cppblog.com/converse/    purpose:    FlyWeight模式的演示代码*********************************************************************/#include "FlyWeight.h"#include <iostream>inline STATE Flyweight::GetIntrinsicState(){    return m_State;}FlyweightFactory::~FlyweightFactory(){    std::list<Flyweight*>::iterator iter1, iter2, temp;    for (iter1 = m_listFlyweight.begin(), iter2 = m_listFlyweight.end();        iter1 != iter2;        )    {        temp = iter1;        ++iter1;        delete (*temp);    }    m_listFlyweight.clear();}Flyweight* FlyweightFactory::GetFlyweight(const STATE& key){    std::list<Flyweight*>::iterator iter1, iter2;    for (iter1 = m_listFlyweight.begin(), iter2 = m_listFlyweight.end();         iter1 != iter2;         ++iter1)    {        if ((*iter1)->GetIntrinsicState() == key)        {            std::cout << "The Flyweight:" << key << " already exits"<< std::endl;            return (*iter1);        }    }    std::cout << "Creating a new Flyweight:" << key << std::endl;    Flyweight* flyweight = new ConcreateFlyweight(key);    m_listFlyweight.push_back(flyweight);}void ConcreateFlyweight::Operation(STATE& ExtrinsicState){}

3)Main.cpp

/********************************************************************    created:    2006/07/26    filename:     Main.cpp    author:        李创                http://www.cppblog.com/converse/    purpose:    FlyWeight模式的测试代码*********************************************************************/#include "FlyWeight.h"int main(){    FlyweightFactory flyweightfactory;    flyweightfactory.GetFlyweight("hello");    flyweightfactory.GetFlyweight("world");    flyweightfactory.GetFlyweight("hello");    system("pause");    return 0;}