Create a ComboBox web control with jQuery and ASP.NET

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Web.UI.WebControls;
using System.Web.UI;
using System.ComponentModel;

[assembly: TagPrefix("Demo", "Sample")]
namespace Demo.WebControls
{
    /// <summary>
    /// ComboBox web control
    /// </summary>
    [DefaultProperty("Text")]
    [ToolboxData("<{0}:ComboBox runat=\"server\"></{0}:ComboBox>")]
    public class ComboBox : TextBox
    {
        private DropDownList _ddl; //this is used to keep ComboBox items in HTML

        /// <summary>
        /// DataSource
        /// </summary>
        [Category("Data")]
        public object DataSource
        {
            get
            {
                EnsureChildControls();
                return _ddl.DataSource;
            }
            set
            {
                EnsureChildControls();
                _ddl.DataSource = value;
            }
        }

        /// <summary>
        /// DataSource ID
        /// </summary>
        [Category("Data")]
        public string DataSourceID
        {
            get
            {
                EnsureChildControls();
                return _ddl.DataSourceID;
            }
            set
            {
                EnsureChildControls();
                _ddl.DataSourceID = value;
            }
        }

        /// <summary>
        /// DataMember
        /// </summary>
        [Category("Data")]
        public string DataMember
        {
            get
            {
                EnsureChildControls();
                return _ddl.DataMember;
            }
            set
            {
                EnsureChildControls();
                _ddl.DataMember = value;
            }
        }

        /// <summary>
        /// DataTextField
        /// </summary>
        [Category("Data")]
        public string DataTextField
        {
            get
            {
                EnsureChildControls();
                return _ddl.DataTextField;
            }
            set
            {
                EnsureChildControls();
                _ddl.DataTextField = value;
            }
        }

        /// <summary>
        /// DataTextField
        /// </summary>
        [Category("Data")]
        public string DataValueField
        {
            get
            {
                EnsureChildControls();
                return _ddl.DataValueField;
            }
            set
            {
                EnsureChildControls();
                _ddl.DataValueField = value;
            }
        }

        /// <summary>
        /// Items
        /// </summary>
        [
        DesignerSerializationVisibility(DesignerSerializationVisibility.Content),
        PersistenceMode(PersistenceMode.InnerDefaultProperty)
        ]
        public ListItemCollection Items
        {
            get
            {
                EnsureChildControls();
                return _ddl.Items;
            }
        }

        /// <summary>
        /// data bind
        /// </summary>
        public override void DataBind()
        {
            _ddl.DataBind();
        }

        /// <summary>
        /// create child controls
        /// </summary>
        protected override void CreateChildControls()
        {
            _ddl = new DropDownList();
            _ddl.TabIndex = -1;
            _ddl.Style.Add("display", "none"); //DropDownList is hidden and used as datasource in HTML markup of ComboBox
            Controls.Add(_ddl);

            base.CreateChildControls();
        }

        /// <summary>
        /// On Pre Render
        /// </summary>
        /// <param name="e"></param>
        protected override void OnPreRender(EventArgs e)
        {
            base.OnPreRender(e);

            Page.ClientScript.RegisterClientScriptResource(typeof(ComboBox), "Demo.WebControls.Scripts.ComboBox.js");
        }

        /// <summary>
        /// Render
        /// </summary>
        /// <param name="writer"></param>
        protected override void Render(HtmlTextWriter writer)
        {
            EnsureChildControls();

            writer.Write("<span style=\"position:relative;\" ComboBox=\"1\" >");
            base.Render(writer);
            writer.Write("<input type=\"button\" value=\"V\" />");
            _ddl.RenderControl(writer);
            writer.Write("<div style=\"visibility:hidden; background-color:white\"></div>");
            writer.Write("</span>");
        }
    }
}