常见设计模式解析和实现（C++）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使用。比如，在QQ聊天时很多时候你懒得回复又不得不回复，一般会用一些客套的话语敷衍别人，如“呵呵”，“好的”等待之类的，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起来。

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他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。

这里的实现要点就是采用一个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）Flywight.h

#include <string>#include <list>typdef std::string STATE;class Flyweight{public:virtual ~Flyweight(){}STATE GetInstrinsicState();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);};

（2）Flyweight.cpp

#include "Flyweight.h"#include <iostream>inline STATE Flyweight::GetInstrinsicState(){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)->GetInstrinsicState() == key){std::cout << "The Flyweight:" << key << "already exists" << 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

#include "FlyWeight.h"int main(){FlyweightFactory flyweightfactory;flyweightfactory.GetFlyweight("Hell");flyweightfactory.GetFlyweight("world");flyweightfactory.GetFlyweight("Hell");return 0;}