走出MFC子类化的迷宫

if (*lplpfn == NULL)

*lplpfn = oldWndProc; // the first control of that type created

#ifdef _DEBUG

else if (*lplpfn != oldWndProc)

{

TRACE0("Error: Trying to use SubclassWindow with incorrect CWnd\n");

TRACE0("\tderived class.\n");

TRACE3("\thWnd = $%04X (nIDC=$%04X) is not a %hs.\n", (UINT)hWnd,

_AfxGetDlgCtrlID(hWnd), GetRuntimeClass()->m_lpszClassName);

ASSERT(FALSE);

// undo the subclassing if continuing after assert

::SetWindowLong(hWnd, GWL_WNDPROC, (DWORD)oldWndProc);

}

#endif

return TRUE;

}

函数Attach内部如下：

BOOL CWnd::Attach(HWND hWndNew)

{

ASSERT(m_hWnd == NULL); // only attach once, detach on destroy

ASSERT(FromHandlePermanent(hWndNew) == NULL);

// must not already be in permanent map