设计模式之抽象状态模式

【定义】当一个对象的内在状态改变时，允许改变其行为，这个对象看起来像是改变了其类。

【场景】比如看一场电影，有以下状态 买票状态：等待进场验票，进场状态：等待电影开始；看电影状态：等待电影结束；出场状态：等待下一场电影 ；

【UML】

【代码】

#include <iostream>

using namespace std;

class SeeFilm;

class State
{
public:
	virtual void ChangeState(SeeFilm* seeFilm) = 0;
	virtual void ShowState() = 0;
};

class SeeFilm
{
private:
	State* state;
public:
	void SetState(State* s)
	{
		delete state;
		if(NULL != s)
		{
			state = s;
			state->ShowState();
		}
	}

	void ChangeState()
	{
		state->ChangeState(this);
	}
};

class StateFilmOver : public State
{
public:
	virtual void ChangeState(SeeFilm* seeFilm)
	{
		seeFilm->SetState(NULL);
	}
	virtual void ShowState()
	{
		cout<<"Current State: StateFilmOver"<<endl;
	}
};

class StateSeeFilm : public State
{
public:
	virtual void ChangeState(SeeFilm* seeFilm)
	{
		seeFilm->SetState(new StateFilmOver());
	}
	virtual void ShowState()
	{
		cout<<"Current State: StateSeeFilm"<<endl;
	}
};

class StateWaitFilm : public State
{
public:
	virtual void ChangeState(SeeFilm* seeFilm)
	{
		seeFilm->SetState(new StateSeeFilm());
	}
	virtual void ShowState()
	{
		cout<<"Current State: StateWaitFilm"<<endl;
	}
};

class StateGetTicket : public State
{
public:
	virtual void ChangeState(SeeFilm* seeFilm)
	{
		seeFilm->SetState(new StateWaitFilm());
	}
	virtual void ShowState()
	{
		cout<<"Current State: StateGetTicket"<<endl;
	}
};

int main()
{
	SeeFilm* seeFilm = new SeeFilm();
	State* state = new StateGetTicket();
	seeFilm->SetState(state);

	seeFilm->ChangeState();
	seeFilm->ChangeState();
	seeFilm->ChangeState();

	delete seeFilm;
	return 0;
}