virtual DROPEFFECT OnDragOver(CWnd* pWnd, COleDataObject* pDataObject, DWORD dwKeyState, CPoint point);
    virtual BOOL OnDrop(CWnd* pWnd, COleDataObject* pDataObject, DROPEFFECT dropEffect, CPoint point);
    virtual DROPEFFECT OnDropEx(CWnd* pWnd, COleDataObject* pDataObject, DROPEFFECT dropDefault, DROPEFFECT dropList, CPoint point);