设计模式（十六）state

1.使用场景：某些对象的状态如果发生改变，其行为也会改变
如：文档的只读状态
2.定义：允许对象在内部状态改变时改变它的行为
。从而使对象看起来似乎修改了其行为
3.类似：strategy
协作：Singleton

原代码：

enum NetworkState
{
    Network_Open,
    Network_Close,
    Network_Connect,
};

class NetworkProcessor{
    
    NetworkState state;

public:
    
    void Operation1(){
        if (state == Network_Open){

            //**********
            state = Network_Close;
        }
        else if (state == Network_Close){

            //..........
            state = Network_Connect;
        }
        else if (state == Network_Connect){

            //$$$$$$$$$$
            state = Network_Open;
        }
    }

    public void Operation2(){

        if (state == Network_Open){
            
            //**********
            state = Network_Connect;
        }
        else if (state == Network_Close){

            //.....
            state = Network_Open;
        }
        else if (state == Network_Connect){

            //$$$$$$$$$$
            state = Network_Close;
        }
    
    }

    public void Operation3(){

    }
};

state设计模式代码：

class NetworkState{

public:
    NetworkState* pNext;
    virtual void Operation1()=0;
    virtual void Operation2()=0;
    virtual void Operation3()=0;

    virtual ~NetworkState(){}
};


class OpenState :public NetworkState{
    
    static NetworkState* m_instance;
public:
    static NetworkState* getInstance(){
        if (m_instance == nullptr) {
            m_instance = new OpenState();
        }
        return m_instance;
    }

    void Operation1(){
        
        //**********
        pNext = CloseState::getInstance();
    }
    
    void Operation2(){
        
        //..........
        pNext = ConnectState::getInstance();
    }
    
    void Operation3(){
        
        //$$$$$$$$$$
        pNext = OpenState::getInstance();
    }
    
    
};

class CloseState:public NetworkState{ }
//...


class NetworkProcessor{
    
    NetworkState* pState;
    
public:
    
    NetworkProcessor(NetworkState* pState){
        
        this->pState = pState;
    }
    
    void Operation1(){
        //...
        pState->Operation1();
        pState = pState->pNext;
        //...
    }
    
    void Operation2(){
        //...
        pState->Operation2();
        pState = pState->pNext;
        //...
    }
    
    void Operation3(){
        //...
        pState->Operation3();
        pState = pState->pNext;
        //...
    }

};