C++享元模式详解

#include <iostream>
#include <list>
#include <map>
using namespace std;


enum class  EnumColor //棋子类型
{
	Black, //黑
	White  //白
};

struct Position //棋子位置
{
	int m_x;
	int m_y;
	Position(int tmpx, int tmpy) :m_x(tmpx), m_y(tmpy) {} //构造函数			
};

/*棋子类*/
class Piece 
{
public:
	//构造函数
	Piece(EnumColor tmpcolor, Position tmppos) :m_color(tmpcolor), m_pos(tmppos){}
	//棋子的绘制
	void draw()
	{
		if(m_color == EnumColor::Black)
		{
			cout << "在位置:(" << m_pos.m_x << "," << m_pos.m_y << ")处绘制了一个黑色棋子!" << endl;
		}
		else
		{
			cout << "在位置:(" << m_pos.m_x << "," << m_pos.m_y << ")处绘制了一个白色棋子!" << endl;
		}
	}
private:
	EnumColor m_color; //棋子颜色
	Position m_pos; //棋子位置
};

int main()
{
	//检测内存泄漏
	_CrtSetDbgFlag(_CRTDBG_ALLOC_MEM_DF | _CRTDBG_LEAK_CHECK_DF);

	Piece* p_piece1 = new Piece(EnumColor::Black, Position(3, 3)); //黑色落子到3,3位置
	p_piece1->draw();

	Piece* p_piece2 = new Piece(EnumColor::White, Position(5, 5)); //白色落子到5,5位置
	p_piece2->draw();

	Piece* p_piece3 = new Piece(EnumColor::Black, Position(4, 6)); //黑色落子到4,6位置
	p_piece3->draw();

	Piece* p_piece4 = new Piece(EnumColor::White, Position(5, 7)); //白色落子到5,7位置
	p_piece4->draw();
	
	//释放资源
	delete p_piece1;
	delete p_piece2;
	delete p_piece3;
	delete p_piece4;
	return 0;
}

62E757AA-6F56-1FB6-793A-4F7B99EB7832.png

对于上面的例程来说,棋子的类型无非就是两种,黑和白,在实际的下棋过程当中,只有位置是不一样的,但是却衍生出了多个具有相似度的对象,我们能否进行改造一下,比如,对象只有两个,黑和白,在实际的运转的时候,改变他们的位置就可以了,这样就不用new很多给相似的对象出来了。下面我们进行改造一下。引入享元模式。

#include <iostream>
#include <list>
#include <map>
using namespace std;


enum EnumColor //棋子类型
{
	Black, //黑
	White  //白
};

struct Position //棋子位置
{
	int m_x;
	int m_y;
	Position(int tmpx, int tmpy) :m_x(tmpx), m_y(tmpy) {} //构造函数			
};

class Piece //棋子抽象类
{
public:
	virtual ~Piece() {} 
public:
	virtual void draw(Position tmppos) = 0;
};


class BlackPiece :public Piece //黑色棋子
{
public:
	virtual void draw(Position tmppos)
	{
		cout << "在位置:(" << tmppos.m_x << "," << tmppos.m_y << ")处绘制了一个黑色棋子!" << endl;
	}
};


class WhitePiece :public Piece //白色棋子
{
public:
	virtual void draw(Position tmppos)
	{
		cout << "在位置:(" << tmppos.m_x << "," << tmppos.m_y << ")处绘制了一个白色棋子!" << endl;
	}
};


class pieceFactory //创建棋子的工厂
{
public:
	virtual ~pieceFactory()
	{
		//释放内存
		for(auto iter = m_FlyWeightMap.begin(); iter != m_FlyWeightMap.end(); ++iter)
		{
			Piece* tmpfw = iter->second;
			delete tmpfw;
		}
		m_FlyWeightMap.clear(); 
	}

	//获取享元对象,也就是获取被共享的棋子对象
	Piece* getFlyWeight(EnumColor tmpcolor)
	{
		auto iter = m_FlyWeightMap.find(tmpcolor);
		if(iter == m_FlyWeightMap.end())
		{
			//没有该享元对象,那么就创建出来
			Piece* tmpfw = nullptr;
			if(tmpcolor == Black) //黑子
			{
				tmpfw = new BlackPiece();
			}
			else //白子
			{
				tmpfw = new WhitePiece();
			}
			//以棋子颜色枚举值作为key,增加条目到map中
			m_FlyWeightMap.insert(make_pair(tmpcolor, tmpfw)); 
			return tmpfw;
		}
		else
		{
			return iter->second;
		}
	}
private:
	std::map<EnumColor, Piece*> m_FlyWeightMap; //享元池,用map容器来保存所有的享元对象,一共就两个享元对象(黑色棋子一个,白色棋子一个)
};

int main()
{
	//检测内存泄漏
	_CrtSetDbgFlag(_CRTDBG_ALLOC_MEM_DF | _CRTDBG_LEAK_CHECK_DF);

	pieceFactory* pfactory = new pieceFactory();

	Piece* p_piece1 = pfactory->getFlyWeight(Black);
	p_piece1->draw(Position(3, 3));  //黑子落子到3,3位置

	Piece* p_piece2 = pfactory->getFlyWeight(White);
	p_piece2->draw(Position(5, 5));  //白子落子到5,5位置

	Piece* p_piece3 = pfactory->getFlyWeight(Black);
	p_piece3->draw(Position(4, 6));  //黑子落子到4,6位置

	Piece* p_piece4 = pfactory->getFlyWeight(White);
	p_piece4->draw(Position(5, 7));  //白子落子到5,7位置

	//释放资源
	delete  pfactory;
	return 0;
}

651ECBCB-DCA0-BDA9-98DC-878E36ADE465.png

454B2D73-63B5-164B-8069-AD77E3C77092.png

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