十二、狀態模式

狀態模式（State） 當一個對象的內在狀態改變時允許改變其行爲，這個對象看起來像是改變了其類。

//state.h
#ifndef _STATE_H_
#define _STATE_H_
class Context;
class State
{
public:
	virtual void Handle(Context* context)=0;
};
class ConcreteStateA:public State
{
public:
	void Handle(Context* context);
};
class ConcreteStateB:public State
{
public:
	void Handle(Context* context);
};

#endif

//state.cpp
#include "State.h"
#include "Context.h"
#include <iostream>
using namespace std;
void ConcreteStateA::Handle(Context* context)
{
	context->SetState(new ConcreteStateB());
	cout<<"new state: stateB..."<<endl;
}
void ConcreteStateB::Handle(Context* context)
{
	context->SetState(new ConcreteStateA());
	cout<<"new state: stateA..."<<endl;
}

//context.h
#ifndef _CONTEXT_H
#define _CONTEXT_H
#include "State.h"
class State;
class Context
{
public:
	Context(State* st);
	void SetState(State* st);
public:
	void Request();
private:
	State* _st;
};
#endif

//context.cpp
#include "Context.h"
#include "State.h"
Context::Context(State* st)
{
	this->_st = st;
}
void Context::SetState(State* st)
{
	this->_st = st;
}

void Context::Request()
{
	_st->Handle(this);
}

//main.cpp
#include "State.h"
#include "Context.h"
int main()
{
	Context* c = new Context(new ConcreteStateA());
	c->Request();
	c->Request();
	return 0;
}