給TEXTBOX添加文字水印

 

  private string _emptyTextTip="*";
        private Color _emptyTextTipColor = Color.Red;

        private const int WM_PAINT = 0xF;

        public ValiTextBox()
            : base()
        {
        }

        [DefaultValue("*")]
        public string EmptyTextTip
        {
            get { return _emptyTextTip; }
            set
            {
                _emptyTextTip = value;
                base.Invalidate();
            }
        }

        [DefaultValue(typeof(Color), "DarkGray")]
        public Color EmptyTextTipColor
        {
            get { return _emptyTextTipColor; }
            set
            {
                _emptyTextTipColor = value;
                base.Invalidate();
            }
        }

        protected override void WndProc(ref Message m)
        {
            base.WndProc(ref m);
            if (m.Msg == WM_PAINT)
            {
                WmPaint(ref m);
            }
        }

   
        private void WmPaint(ref Message m)
        {
            using (Graphics graphics = Graphics.FromHwnd(base.Handle))
            {
                if (Text.Length == 0
                    && !string.IsNullOrEmpty(_emptyTextTip)
                    && !Focused)
                {
                    TextFormatFlags format =
                        TextFormatFlags.EndEllipsis |
                        TextFormatFlags.VerticalCenter;

                    if (RightToLeft == RightToLeft.Yes)
                    {
                        format |= TextFormatFlags.RightToLeft | TextFormatFlags.Right;
                    }

                   TextRenderer.DrawText(
                       graphics,
                       _emptyTextTip,
                      Font,
                     base.ClientRectangle,
                      _emptyTextTipColor,
                      format);

                  //下面代碼是在TextBox後面加入水印

                    //TextRenderer.DrawText(
                     / /  graphics,
                     //   _emptyTextTip,
                      //  Font,
                      //  new Point(this.Width - 15, 10),
                     //   _emptyTextTipColor,
                    //    format);
                }
              
            }
        }