更改CComboBox的边框颜色以显示错误和警告

class CMyComboBox : public CComboBox
{
    DECLARE_DYNAMIC(CMyComboBox)

public:
    CMyComboBox();
    virtual ~CMyComboBox();

protected:
    afx_msg HBRUSH CtlColor(CDC* pDC, UINT nCtlColor);
    DECLARE_MESSAGE_MAP()
};

IMPLEMENT_DYNAMIC(CMyComboBox, CComboBox)

CMyComboBox::CMyComboBox()
{
}

CMyComboBox::~CMyComboBox()
{
}

BEGIN_MESSAGE_MAP(CMyComboBox, CComboBox)
    ON_WM_CTLCOLOR()
END_MESSAGE_MAP()

HBRUSH CMyComboBox::CtlColor(CDC* pDC, UINT nCtlColor)
{
    HBRUSH hbr = CComboBox::CtlColor(pDC, nCtlColor);

    // 根据需要设置边框颜色
    if (nCtlColor == CTLCOLOR_EDIT)
    {
        // 设置错误状态下的边框颜色为红色
        if (IsWindowEnabled() && IsWindowVisible() && GetEditSel() == 0)
        {
            pDC->SetTextColor(RGB(255, 0, 0));
            pDC->SetBkColor(RGB(255, 255, 255));
            pDC->SetBkMode(TRANSPARENT);
            CPen pen(PS_SOLID, 1, RGB(255, 0, 0));
            CPen* pOldPen = pDC->SelectObject(&pen);
            CRect rect;
            GetClientRect(rect);
            rect.DeflateRect(1, 1);
            pDC->Rectangle(rect);
            pDC->SelectObject(pOldPen);
        }
        // 设置警告状态下的边框颜色为黄色
        else if (IsWindowEnabled() && IsWindowVisible() && GetEditSel() != 0)
        {
            pDC->SetTextColor(RGB(0, 0, 0));
            pDC->SetBkColor(RGB(255, 255, 0));
            pDC->SetBkMode(TRANSPARENT);
            CPen pen(PS_SOLID, 1, RGB(255, 255, 0));
            CPen* pOldPen = pDC->SelectObject(&pen);
            CRect rect;
            GetClientRect(rect);
            rect.DeflateRect(1, 1);
            pDC->Rectangle(rect);
            pDC->SelectObject(pOldPen);
        }
    }

    return hbr;
}