关于三级联动数据绑定有关问题，小弟我用后台绑定数据，感觉不太协调，能不能优化一下

关于三级联动数据绑定问题，我用后台绑定数据，感觉不太协调，能不能优化一下？
后台数据绑定

protected void TextBox1_TextChanged(object sender, EventArgs e)

        {

            string id = TextBox1.Text;

            SqlParameter[] val = new SqlParameter[] { 

            new SqlParameter("@id",id)

            };

            string sql = "select color from ruku where id=@id";

            DataTable dt = DAL.DBHelper.GetDataSet(sql,val);

            //DataTable dt1 = new DataTable();

            //dt1.Columns.Add("col", typeof(System.String));

            

            List<string> list = new List<string>();

            foreach (DataRow r in dt.Rows)

            {

                string vale = r["color"].ToString();

                if (!list.Contains(vale))

                {

                    list.Add(vale);

                }

            }

            DropDownList1.DataSource = list;

            DropDownList1.DataBind();

        }

前台代码

<div>

        编号：<asp:TextBox ID="TextBox1" runat="server" AutoPostBack="True" OnTextChanged="TextBox1_TextChanged"></asp:TextBox>

        &nbsp;&nbsp;&nbsp; 颜色：<asp:DropDownList ID="DropDownList1" Width="100px" runat="server">

        </asp:DropDownList>

        &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;

        <asp:Button ID="Button1" runat="server" Text="查  询" Width="94px" OnClientClick="return fun()"

            OnClick="Button1_Click" />

    </div>

------解决方案--------------------
Refer here:
http://www.cnblogs.com/insus/archive/2011/07/04/2097059.html
http://www.cnblogs.com/insus/archive/2012/10/16/2725307.html
http://www.cnblogs.com/insus/p/3414480.html
http://www.cnblogs.com/insus/p/3426563.html