状态模式 State

状态模式(State)，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。

Context中有成员变量标志其状态，在每次请求过后，在具体状态类中设置其变化至的类。

// State.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <iostream>
#include <string>
using namespace std;

class State;
class Context{
public:
    Context(){
        m_pstate = NULL;
    }
    void setState(State * pstate){
        m_pstate = pstate;
    }
    State * getState(){
        return m_pstate;
    }
    void request();

    ~Context(){
        delete m_pstate;
    }
private:
    State * m_pstate;
};

class State{
public:
    virtual void handle(Context * pcontext) = 0;
};
void Context::request(){

    if(this->m_pstate != NULL)
        this->m_pstate->handle(this);
    else
        cout<<"not set the origin state"<<endl;
}

class ConcreateState1:public State{
public:
    void handle(Context * pcontext);
};

class ConcreateState2:public State{
public:
    void handle(Context * pcontext);
};

class ConcreateState3:public State{    //当添加具体状态3时，添加状态3类，并在状态2中调整handle，将下一个状态设置为状态3，可以类比于链表
public:
    void handle(Context * pcontext);
};

void ConcreateState1::handle(Context * pcontext){
    cout<<"state1 "<<endl;
    delete pcontext->getState();
    pcontext->setState(new ConcreateState2);
}
void ConcreateState2::handle(Context * pcontext){
    cout<<"state2 "<<endl;
    delete pcontext->getState();
    pcontext->setState(new ConcreateState3);
}
void ConcreateState3::handle(Context * pcontext){
    cout<<"state3 "<<endl;
    delete pcontext->getState();
    pcontext->setState(new ConcreateState1);
}

int main(int argc, char* argv[])
{
    Context * pcontext = new Context;
    pcontext->setState(new ConcreateState1);   //设置当前状态
    for (int i = 0;i<10;i++)
    {
        pcontext->request();
    }
    delete pcontext;
    return 0;
}