在lbuttondown中加入setcaptrue函数无效

void CChildView::OnMouseMove(UINT nFlags, CPoint point)
{
    // TODO: 在此添加消息处理程序代码和/或调用默认值

    if (m_pmousemove == true)   //如果m_pmousemove为真，则画出点画线
    {
        CClientDC dc(this);


        int n01mode = dc.SetROP2(R2_NOT);
        dc.MoveTo(m_pfrom);
        dc.LineTo(m_pto);
        dc.SetROP2(n01mode);
        dc.MoveTo(m_pfrom);
        dc.LineTo(point);
        m_pto = point;
    }

    CWnd::OnMouseMove(nFlags, point);
}

void CChildView::OnLButtonDown(UINT nFlags, CPoint point)
{
    // TODO: 在此添加消息处理程序代码和/或调用默认值

    if (m_pmousemove == false)
    {
        m_pmousemove = true;
        m_pfrom = point;
        m_pto = point;
        SetCapture();
    }
    else
    {
        m_pmousemove = false;
        ::ReleaseCapture();
    }

    CWnd::OnLButtonDown(nFlags, point);
}

调试的时候如果用getcaptrue（）测试的话，是成功的，但是点画线就是出不去，麻烦大佬们解答

画线的代码要放在paint里面，在mousemove里面不要直接画，而是应该把坐标纪录下来，然后刷新客户区，让onpaint调用