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;
}