public class Xtxt3 : TextBox

    {

        private bool m_underLine;

        public bool UnderLine

        {

            get { return m_underLine; }

            set

            {

                if (this.m_underLine != value)

                {

                    if (value)

                    {

                        this.BorderStyle = BorderStyle.None;

                    }

                    m_underLine = value;

                }

            }

        }

        protected override void WndProc(ref Message m)

        {

            base.WndProc(ref m);

            if (m.Msg == 0xf || m.Msg == 0x14 || m.Msg == 0x85)

            {

                if (this.BorderStyle == BorderStyle.None)

                {

                    if (m_underLine)

                    {

                        using (Graphics g = Graphics.FromHwnd(this.Handle))

                        {

                            g.DrawLine(SystemPens.ControlText, 0, this.Height - 1, this.Width - 1, this.Height - 1);

                        }

                    }

                }

            }

        }

    }