//Style
<style type="text/css">
        .AutoExtender
        {
            font-family: Verdana, Helvetica, sans-serif;
            font-size: 1.0em;
            font-weight: normal;
            border: solid 1px #95BF4E;
            line-height: 20px;
            padding: 10px;
            background-color: White;
            margin-left: 7px;
            z-index: 100000;
            overflow-y: scroll;
        }
        .AutoExtenderList
        {
            border-bottom: dotted 1px #95BF4E;
            cursor: pointer;
            color: Maroon;
        }
        .AutoExtenderHighlight
        {
            color: White;
            background-color: #95BF4E;
            cursor: pointer;
        }
        #divwidth
        {
            width: 160px !important;
            height: 170px;
        }
        #divwidth div
        {
            width: 150px !important;
        }
        .watermarkfoodname
        {
            background-color: #F0F8FF;
            color: #808080;
        }
    </style>


//Code on aspx page



<div id="divwidth">
                                                                </div>
                                                                <asp:TextBox ID="txtAddMyFoodName" runat="server" Width="140px" Height="22px" onkeyup="clearUnit();"
                                                                    onblur="showUnit()"></asp:TextBox>
                                                                <%--<input type="hidden" runat="server" id="hdnProductId" />--%>
                                                                <ajaxToolkit:AutoCompleteExtender BehaviorID="bhvrSearch" runat="server" ID="AutoCompleteExtender1"
                                                                    TargetControlID="txtAddMyFoodName" ServiceMethod="GetFoodompletionList" UseContextKey="true"
                                                                    MinimumPrefixLength="1" CompletionInterval="1" ContextKey="0" EnableCaching="true"
                                                                    CompletionListElementID="divwidth" CompletionListCssClass="AutoExtender" CompletionListItemCssClass="AutoExtenderList"
                                                                    CompletionListHighlightedItemCssClass="AutoExtenderHighlight" OnClientItemSelected="FillCurrentStock" />
                                                                <ajaxToolkit:TextBoxWatermarkExtender ID="TBWE2" runat="server" TargetControlID="txtAddMyFoodName"
                                                                    WatermarkText="Type Food Name Here" WatermarkCssClass="watermarkfoodname" />


//Code on Code behind File


#region GetCodeCompletionList
    /// <summary>
    /// This function is calling by product list control
    /// </summary>
    /// <creted by>Harish Kumar Chandna</creted by>
    /// <creation date>17 AUGUST 2011</creation date>
    /// <param name="prefixText"></param>
    /// <param name="count"></param>
    /// <param name="contextKey"></param>
    /// <returns></returns>
    [System.Web.Services.WebMethod]
    [System.Web.Script.Services.ScriptMethod]
    public static string[] GetFoodompletionList(string prefixText, int count, string contextKey)
    {
        try
        {
            List<String> suggestions = new List<string>();
            DataSet ds = new DataSet();
            //Fetch the products
            DPService.DiabetesPilotServiceClient objService = new DPService.DiabetesPilotServiceClient();
            ds = objService.FoodSearch(prefixText, 0);
            //Traverse the entire products in list
            foreach (DataRow drow in ds.Tables[0].Rows)
            {
                string html = drow["Food_Name"].ToString();
                string item = AjaxControlToolkit.AutoCompleteExtender.CreateAutoCompleteItem(drow["Food_Name"].ToString(), html);
                suggestions.Add(item);
            }
            return suggestions.ToArray();
        }
        catch (Exception ex)
        {
            throw ex;
        }

    }
    #endregion