看到很多网站上的输入框都有空值提示，即：输入框中没有内容且没有焦点时，输入框中显示的是提示文字；如果有内容或者拥有焦点，则正常显示。我觉得这东西很有意思，在某些应用中，可以减少界面排版上的麻烦，可惜WinForm中的TextBox没有此功能，于是自己做了一个，效果嘛，还算满意的：）

    public class TEditBox : System.Windows.Forms.TextBox
    {
        public TEditBox()
            : base()
        {
        }

        private string _Caption = "Please Input";
        /// <summary>
        /// 提示内容
        /// </summary>
        public string Caption
        {
            get
            {
                return _Caption;
            }
            set
            {
                _Caption = value;
                if (!DesignMode && Nothing)
                    base.Text = value;
            }
        }

        private System.Drawing.Color _CaptionColor = System.Drawing.SystemColors.Control;
        /// <summary>
        /// 提示字体的颜色
        /// </summary>
        public System.Drawing.Color CaptionColor
        {
            get
            {
                return _CaptionColor;
            }
            set
            {
                if (!DesignMode && !Focused && Nothing)
                    base.ForeColor = value;
                
                _CaptionColor = value;
            }
        }

        private System.Drawing.Color _ForeColor = System.Drawing.SystemColors.WindowText;

        public new System.Drawing.Color ForeColor
        {
            get
            {
                return base.ForeColor;
            }
            set
            {
                if (!this.DesignMode)
                {
                    if (Focused || !Nothing)
                        base.ForeColor = value;
                    _ForeColor = value;
                }
                else
                    base.ForeColor = value;
            }
        }

        private bool HaveNothing = true;
        private bool Nothing
        {
            get { return HaveNothing || this.Text == ""; }
        }

        public new string Text
        {
            get
            {
                if (!Focused && HaveNothing)
                    return "";
                else
                    return base.Text;
            }
            set
            {
                base.Text = value;
                HaveNothing = value == "";

                if (Nothing && !Focused)
                {
                    base.Text = _Caption;
                    base.ForeColor = _CaptionColor;
                }
                else
                {
                    if (base.ForeColor != _ForeColor)
                        base.ForeColor = _ForeColor;
                }
            }
        }

        protected override void OnGotFocus(EventArgs e)
        {
            if (Nothing)
                base.Text = "";

            if (base.ForeColor != _ForeColor)
                base.ForeColor = _ForeColor;

            base.OnGotFocus(e);
        }

        protected override void OnLostFocus(EventArgs e)
        {
            HaveNothing = base.Text == "";

            if (Nothing)
            {
                base.Text = _Caption;
                base.ForeColor = _CaptionColor;
            }
            else
            {
                if (base.ForeColor != _ForeColor)
                    base.ForeColor = _ForeColor;
            }
            base.OnLostFocus(e);
        }

        public new void Clear()
        {
            this.Text = "";
        }        
    }

属性Caption和CaptionColor是新增的，用来存储提示文字和提示文字的颜色