允許對象在內部狀態發生改變時改變它的行為，對象看起來好像修改了它的類。

在state模式中我們將狀態邏輯和動作實現進行分離。當一個操作中要維護大量的 case 分支語句，並且這些分支依賴於對象的狀態。state模式將每一個分支都封裝到獨立的類中。

代碼:

#include <iostream>
using namespace std;

#define CC_SAFE_DELETE(p) if ((p)) {delete (p); (p) = NULL;}

class Work;

class State
{
public:
    virtual ~State() {}
 
public:
    virtual void writeProgram(Work *w) = 0;
};

// 上午工作狀態
class ForenoonState : public State
{
public:
    virtual void writeProgram(Work *w);
};

// 中午工作狀態
class NoonState : public State
{
public:
    virtual void writeProgram(Work *w);
};

// 下午工作狀態
class AfternoonState : public State
{
public:
    
 
virtual void writeProgram(Work *w);
};

// 晚間工作狀態
class EveningState : public State
{
public:
    virtual void writeProgram(Work *w);
};

// 睡眠狀態
class SleepingState : public State
{
public:
    virtual void writeProgram(Work *w);
};

// 下班休息狀態
class RestState : public State
{
public:
    virtual void writeProgram(Work *w);
};

 
class Work
{
public:
    Work()
    {
        _curState = new ForenoonState();
        _taskFinished = false;
    }

    ~Work()
    {
        CC_SAFE_DELETE(_curState);
    }
    inline void setHour(int h){ _hour = h; }
    inline int getHour(){ return _hour; }
    inline bool getTaskFinished(){ return _taskFinished; }
    void setTaskFinished(bool finished = true){ _taskFinished = finished; }

    void changeState(State *s)
    {
        if (_curState != s)
        {
            CC_SAFE_DELETE(_curState);
            _curState = s;
        }
    }

    void writeProgram()
    {
        _curState->writeProgram(this);
    }

    
private:
    int _hour;    //時間
    State *_curState;  //工作狀態
    bool _taskFinished;
};


void ForenoonState::writeProgram(Work *w)
{
    if (w->getHour() < 12)
    {
        cout << "當前時間: " << w->getHour() << "點 上午工作，精神百倍" << endl;
    }
    else
    {
        w->changeState(new NoonState());
        w->writeProgram();
    }
}

void NoonState::writeProgram(Work *w)
{
    if (w->getHour() < 13)
    {
        cout << "當前時間: " << w->getHour() << "點 午休時間" << endl;
    }
    else
    {
        w->changeState(new AfternoonState());
        w->writeProgram();
    }
}

void AfternoonState::writeProgram(Work *w)
{
    if (w->getHour() < 18)
    {
        cout << "當前時間: " << w->getHour() << "點 下午狀態不錯， 努力工作" << endl;
    }
    else
    {
        w->changeState(new EveningState());
        w->writeProgram();
    }
}

void EveningState::writeProgram(Work *w)
{
    if (w->getTaskFinished())
    {
        w->changeState(new RestState()); // 下班
        w->writeProgram();
    }
    else
    {
        if (w->getHour() < 22)
        {
            cout << "當前時間: " << w->getHour() << "點 加班哦, 疲憊至極" << endl;
        }
        else
        {
            w->changeState(new SleepingState());
            w->writeProgram();
        }
    }
}

void RestState::writeProgram(Work *w)
{
    cout << "當前時間是: " << w->getHour() << "點 下班回家了" << endl;
}

void SleepingState::writeProgram(Work *w)
{
    cout << "當前時間是: " << w->getHour() << "點, 不行了,睡覺了" << endl;
}

void test()
{
    Work *w = new Work();
    w->setHour(9);
    w->writeProgram();
    w->setHour(10);
    w->writeProgram();
    w->setHour(12);
    w->writeProgram();
    w->setHour(14);
    w->writeProgram();
    w->setHour(19);
    w->writeProgram();
    //w->setTaskFinished();
    w->setHour(20);
    w->writeProgram();
    w->setHour(23);
    w->writeProgram();
}

int main()
{
    test();
    cin.get();
    return 0;
}

效果:

狀態模式