c++之状态模式

状态模式

定义：当一个对象的内在状态改变时，允许改变它的行为，这个对象看起来像是改变了其类。

它属于行为型模式

栗子场景：一天根据当前的时间段，来决定一个人是吃早饭还是午饭以及晚饭。即根据时间的状态变化，改变人吃什么的行为。

代码：

#include <iostream>
#include <Windows.h>

using namespace std;

class Eat;

class MealStatus
{
public:
	virtual void doEat(Eat *eat) = 0;
};

class Eat{
public:
	Eat(MealStatus *m) :m_status(nullptr)
	{
		m_status = m;
	}
	~Eat()
	{
		if (m_status)
		{
			delete m_status;
			m_status = nullptr;
		}
	}

	void request()
	{
		m_status->doEat(this);
	}

	void setStatus(MealStatus* s)
	{
		m_status = s;
	}

	void setHour(int h)
	{
		m_hour = h;
	}

	int getHour()
	{
		return m_hour;
	}

private:
	MealStatus* m_status;
	int m_hour;
};

//夜宵
class NightSnack :public MealStatus
{
public:
	NightSnack(){}
	void doEat(Eat *eat)
	{
		cout << "吃夜宵时间段来了，吃货的一天准备结束啦" << " current-time=" << eat->getHour() << endl;
	}
};

//晚餐
class Dinner :public MealStatus
{
public:
	Dinner(){}
	void doEat(Eat *eat)
	{
		if (eat->getHour() < 21)
		{
			cout << "吃晚饭时间段" << " current-time=" << eat->getHour() << endl;
		}
		else
		{
			eat->setStatus(new NightSnack);
			eat->request();
		}		
	}
};

//午餐
class Lunch :public MealStatus
{
public:
	Lunch(){}
	void doEat(Eat *eat)
	{
		if (eat->getHour()<14)
		{
			cout << "吃午饭时间段" << " current-time="<<eat->getHour()<<endl;
		}
		else
		{
			eat->setStatus(new Dinner);
			eat->request();
		}
	}
};

//早餐
class Breakfast :public MealStatus
{
public:
	Breakfast(){}
	void doEat(Eat *eat)
	{
		if (eat->getHour() < 9)
		{
			cout << "吃早饭时间段" << " current-time=" << eat->getHour()<< endl;
		}
		else
		{
			eat->setStatus(new Lunch);
			eat->request();
		}

	}
};

int main()
{
	Eat *eat = new Eat(new Breakfast);

	//切换状态
	eat->setHour(8);
	eat->request();

	eat->setHour(13);
	eat->request();

	eat->setHour(20);
	eat->request();

	eat->setHour(24);
	eat->request();

	if (eat)
	{
		delete eat;
		eat = nullptr;
	}

	return 0;
}

效果