设计模式读书笔记：Flyweight（享元）

意图：

运用共享技术有效地支持大量细粒度的对象。

结构图：来自 《23种设计模式 - 郗晓勇》



实现：https://github.com/panshiqu/patterns/tree/master/Flyweight

FlyweightFactory

#include "ConcreteFlyweight.h"
#include <map>

namespace NS_FLYWEIGHT {

class FlyweightFactory {
public:
FlyweightFactory() {}
virtual ~FlyweightFactory()
{
std::map<int, Flyweight *>::iterator itr = _flyweights.begin();
for (; itr != _flyweights.end(); itr++)
delete itr->second;

_flyweights.clear();
}
Flyweight *getFlyweight(int key)
{
std::map<int, Flyweight *>::iterator itr = _flyweights.find(key);
if (itr != _flyweights.end()) return itr->second;

ConcreteFlyweight *flyweight = new ConcreteFlyweight();
flyweight->setIntrinsicState(key);

_flyweights.insert(std::make_pair(key, flyweight));
return flyweight;
}

private:
std::map<int, Flyweight *> _flyweights;
};

} /* namespace NS_FLYWEIGHT */

Flyweight

#include <iostream>

namespace NS_FLYWEIGHT {

class Flyweight {
public:
Flyweight() {}
virtual ~Flyweight() {}
virtual void operation(std::string extrinsicState) = 0;
};

} /* namespace NS_FLYWEIGHT */

ConcreteFlyweight

#include "Flyweight.h"

namespace NS_FLYWEIGHT {

class ConcreteFlyweight : public Flyweight
{
public:
ConcreteFlyweight() : _intrinsicState(0) {}
virtual ~ConcreteFlyweight() {}
virtual void operation(std::string extrinsicState)
{
std::cout << extrinsicState << " ConcreteFlyweight - " << _intrinsicState << std::endl;
}

void setIntrinsicState(int intrinsicState)	{ _intrinsicState = intrinsicState; }

private:
int _intrinsicState;
};

} /* namespace NS_FLYWEIGHT */

UnsharedConcreteFlyweight

#include "Flyweight.h"
#include <map>

namespace NS_FLYWEIGHT {

class UnsharedConcreteFlyweight : public Flyweight
{
public:
UnsharedConcreteFlyweight() {}
virtual ~UnsharedConcreteFlyweight() {}
virtual void operation(std::string extrinsicState)
{
std::multimap<Flyweight *, std::string>::iterator itr = _flyweights.begin();
for (; itr != _flyweights.end(); itr++)
{
std::string str = itr->second;
if (str == "") str = extrinsicState;

itr->first->operation(str);
}
}
virtual void add(Flyweight *flyweight, std::string extrinsicState)
{
_flyweights.insert(make_pair(flyweight, extrinsicState));
}
virtual void remove(Flyweight *flyweight)
{
// do remove
}

private:
std::multimap<Flyweight *, std::string> _flyweights;
};

} /* namespace NS_FLYWEIGHT */

main

#include "Flyweight/FlyweightFactory.h"
#include "Flyweight/UnsharedConcreteFlyweight.h"
using namespace NS_FLYWEIGHT;
int main(void)
{
FlyweightFactory ff;
UnsharedConcreteFlyweight ucf;
Flyweight *f1 = ff.getFlyweight(1);
ucf.add(f1, "");
Flyweight *f2 = ff.getFlyweight(1);
ucf.add(f2, "black");
ucf.operation("red");
}

附加：