子对话框重绘问题

void C****Dlg::OnPaint()
{
    if (IsIconic())
    {
        CPaintDC dc(this); // device context for painting

        SendMessage(WM_ICONERASEBKGND, reinterpret_cast<WPARAM>(dc.GetSafeHdc()), 0);

        // Center icon in client rectangle
        int cxIcon = GetSystemMetrics(SM_CXICON);
        int cyIcon = GetSystemMetrics(SM_CYICON);
        CRect rect;
        GetClientRect(&rect);
        int x = (rect.Width() - cxIcon + 1) / 2;
        int y = (rect.Height() - cyIcon + 1) / 2;

        // Draw the icon
        dc.DrawIcon(x, y, m_hIcon);
    }
    else
    {
        CPaintDC dc(this);                //对话框的dc
        CDC dcMem;
        dcMem.CreateCompatibleDC(&dc);   //创建与对话框dc兼容的内存dc

        CRect rect;
        GetClientRect(&rect);

        BITMAP bitMap;
        m_bmpBackground.GetBitmap(&bitMap);

        CBitmap *pbmpOld=dcMem.SelectObject(&m_bmpBackground);        //将背景位图选入内存dc中
        dc.StretchBlt(0,0,rect.Width(),rect.Height(),&dcMem,0,0,bitMap.bmWidth,bitMap.bmHeight,SRCCOPY);   //将内存dc中的位图拉伸显示在对话框的dc中
        dcMem.SelectObject(pbmpOld);        //CDialog::OnPaint();
    }
}