(AFX_PMSG)(AFX_PMSGW)(void (AFX_MSG_CALL CWnd::*)(UINT, CPoint))&OnLButtonDown
#define ON_WM_LBUTTONDOWN() \
{ WM_LBUTTONDOWN, 0, 0, 0, AfxSig_vwp, \
(AFX_PMSG)(AFX_PMSGW)(void (AFX_MSG_CALL CWnd::*)(UINT, CPoint))&OnLButtonDown }
(AFX_PMSG)(AFX_PMSGW)(void (AFX_MSG_CALL CWnd::*)(UINT, CPoint))&OnLButtonDown
这句加上&OnLButtonDown怎么理解