本人开发的带提示的TextBox控件

 /// <summary>
    /// created by 章松山 2012-09-20
    /// </summary>
    public class TipTextBox:TextBox
    {
        [Bindable(true)]
        [Category("Appearance")]
        [Localizable(true)]
        public string DefalutText
        {
            get
            {
                String s = (String)ViewState["DefalutText"];
                return ((s == null) ? String.Empty : s.Trim());
            }
            set
            {
                ViewState["DefalutText"] = value;
            }
        }
        public string TipDisplay
        {
            get
            {
                String s = (String)ViewState["TipDisplay"];
                return ((s == null) ? "inline" : s.Trim());
            }
            set
            {
                ViewState["TipDisplay"] = value;
            }
        }
        public string ContentDisplay
        {
            get
            {
                String s = (String)ViewState["ContentDisplay"];
                return ((s == null) ? "none" : s.Trim());
            }
            set
            {
                ViewState["ContentDisplay"] = value;
            }
        }
     
        protected override void RaisePostDataChangedEvent()
        {
            if (!string.IsNullOrEmpty(this.Text))
            {
                TipDisplay = "none";
                ContentDisplay = "inline";  
            }
            else
            {
                TipDisplay = "inline";
                ContentDisplay = "none";  
            }
            base.RaisePostDataChangedEvent();
        }
        protected override void Render(System.Web.UI.HtmlTextWriter writer)
        {
            string tiponclickstr =GetOnclickStr("spantip");
            writer.Write("<span id=\"spantip" + this.ID + "\" style=\"width:" + this.Width.ToString() + ";display:" + TipDisplay + "\" onclick=" + tiponclickstr + ">");
            string htmltip = "<input type=\"text\" style=\"width:" + this.Width.ToString() + ";color:Gray\" value='" + DefalutText + "' id=txtTip" + this.ID + " />";
            writer.Write(htmltip);
            writer.Write("</span>");
            string contentonclickstr = GetOnclickStr("spancontent");
            writer.Write("<span id=\"spancontent" + this.ID + "\" style=\"width:" + this.Width.ToString() + ";display:"+ContentDisplay+"\">");
            base.Render(writer);
            writer.Write("</span>");
        }
        protected override void AddAttributesToRender(System.Web.UI.HtmlTextWriter writer)
        {
            this.Attributes.Add("onblur", GetOnclickStr("spancontent"));
            this.Style.Add("width", this.Width.ToString());
            base.AddAttributesToRender(writer);
        }
        private string GetOnclickStr(string htmlkind)
        {
            string str = string.Empty;
            if (htmlkind == "spantip")
            {
                str = "document.getElementById('spantip" + this.ID + "').style.display='none';";
                str += "document.getElementById('spancontent" + this.ID + "').style.display='inline';";
                str += "document.getElementById('"+this.ClientID + "').focus();";
            }
            else
            {
                str = "if(this.value==''){document.getElementById('spantip" + this.ID + "').style.display='inline';";
                str += "document.getElementById('spancontent" + this.ID + "').style.display='none';}";      
            }
            return str;
        }
    }