实现可编辑下拉框的ComboBox asp.net控件方法

    public class ComboBox:System.Web.UI.WebControls.CompositeControl
    {

        private TextBox input;
        private DropDownList select;

        public TextBox TextBox {

            get { this.EnsureChildControls(); return input; }
        }

        public DropDownList DropDownList {

            get { this.EnsureChildControls(); return select; }
        }



        protected override void CreateChildControls()
        {
            //base.CreateChildControls();

            this.Controls.Clear();
            input = new TextBox();
            input.ID = "input";

            select = new DropDownList();
            select.ID =  "select";

            this.Controls.Add(select);
            this.Controls.Add(input);
            this.ChildControlsCreated = true;
        }
        protected override void RenderContents(System.Web.UI.HtmlTextWriter writer)
        {
            this.EnsureChildControls();

  //           <select id="test1" style="width:100px;height:20px;">
  //<option>中国</option>
  //<option>aaaaa</option>
  //<option>ccccc</option>
  //<option>香港</option>
  //</select>  
  //<div style="width:80px; height:20px; position:absolute;" >
  //<iframe frameborder="0" style="width:100%; height:100%;"></iframe>
  //<input type="text" style="width:78px;height:17px;position:absolute; padding:0;" />
  //</div>
            select.Width = 100;
            select.Height = 20;
            select.RenderControl(writer);
            //div
            writer.AddStyleAttribute("width", "80px");
            writer.AddStyleAttribute("height", "20px");
            writer.AddStyleAttribute("position", "absolute");
            writer.RenderBeginTag(HtmlTextWriterTag.Div);
            //iframe
            writer.AddStyleAttribute("width", "100%");
            writer.AddStyleAttribute("height", "100%");
            writer.AddAttribute("frameborder", "0");
            writer.RenderBeginTag(HtmlTextWriterTag.Iframe);
            writer.RenderEndTag();
            //input
            input.Width = 78;
            input.Height = 15;
            input.Style.Add(HtmlTextWriterStyle.Position, "absolute");
            input.RenderControl(writer);
            //end div
            writer.RenderEndTag();

    //            <script  type="text/javascript">
    //    $(function () {
    //        var select = $('#test1');
    //        var offset = select.offset();
    //        select.change(function () { $(this).next().find('input').val($(this).val()); })
    //        .next().css({ left: offset.left, top: offset.top, zindex: 1000 })
    //        .find('input').css({ left: 0, top: 0, zindex: 1001 });
    //    })
    //</script>
            writer.AddAttribute("type", "text/javascript");
            writer.RenderBeginTag(HtmlTextWriterTag.Script);
            writer.Write("$(function () {var select = $('#" + this.ID + "_" + this.select.ID + "'); var offset = select.offset();");
            writer.Write("select.change(function () { $(this).next().find('input').val($(this).find(':selected').text()); })");
            writer.Write(".next().css({ left: offset.left, top: offset.top, zindex: 1000 })");
            writer.Write(".find('input').css({ left: 0, top: 0, zindex: 1001 });})");
            writer.RenderEndTag();
        
            


        }

    }