设计模式学习-Memento(备忘录)

 

意图:在不破坏封装性的前提下，捕获一个对象的内部状态，并在该对象之外保存这个状态，这样以后就可将该对象恢复到原先保存的状态。

一个备忘录(Memento)是一个对象，它存储另一个对象在某个瞬间的内部状态，而后者称为备忘录的原发器(Originator)

适用性:

必须保持某个对象在某个时刻的状态

如果一个用接口来让其它对象这节得到这些状态，将会暴露对象的实现细节并破坏对象的封装性

示例图:

示例代码:

//线条类
class CLine
{
public:
    CLine(LineState STATE);
public:
    ~CLine(void);
public:
    //移动到目标位置
    void MoveTo(POINT start,POINT end)
    {
        CSolver* pSolver = CSolver::Instance();
        CLineMemento *pMem = pSolver->CreateMemento();   
        pMem->m_State = m_State;           
        _tprintf(_T("Line move from (%d:%d-%d:%d) to (%d:%d-%d:%d)/n"),
                    m_State.Start.x,m_State.Start.y,m_State.End.x,m_State.End.y,start.x,start.y,end.x,end.y);
        m_State.Start = start;
        m_State.End = end;
    }
    //撤销移动
    void UnDoMoveTo()
    {
        LineState state = RestoreMemento();
        _tprintf(_T("Line un move from (%d:%d-%d:%d) to (%d:%d-%d:%d)/n"),
            m_State.Start.x,m_State.Start.y,m_State.End.x,m_State.End.y,state.Start.x,state.Start.y,state.End.x,state.End.y);
        m_State = state;
        CSolver* pSolver = CSolver::Instance();
        CLineMemento *pMem = pSolver->CreateMemento();   
        pMem->m_State = m_State;   
    }
private:   
    LineState RestoreMemento()
    {
        CSolver* pSolver = CSolver::Instance();
        CLineMemento *pMem = pSolver->CreateMemento();       
        return pMem->m_State;
    }
private:
    LineState m_State;
};

//线条备忘类
class CLineMemento
{
friend class CLine;
public:
    CLineMemento();
public:
    ~CLineMemento(void);
    protected:
    LineState m_State;
};

//相对简单的Solver
 class CSolver
{
private:
    CSolver(void);
private:
    ~CSolver(void);
public:
    CLineMemento* CreateMemento()
    {
        if(m_pMem == NULL)
        {
            m_pMem = new CLineMemento();       
        }
        return m_pMem;
    }

public:
    static CSolver* Instance()
    {
        return &m_PInstance;
    }
private:
    static CSolver m_PInstance;
    CLineMemento* m_pMem;
};
也可以支持链表形式的备忘录，用于支持撤销多个操作……