How to Add AutoComplete Ajax extender in Asp.net

aspx source code

 <%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="cc1" %>

<div>
                    <asp:TextBox ID="txtcityname" runat="server"></asp:TextBox>

                     <cc1:AutoCompleteExtender ServiceMethod="Akramsrch"
    MinimumPrefixLength="2"
    CompletionInterval="100" EnableCaching="false" CompletionSetCount="10"
    TargetControlID="txtcityname"
    ID="AutoCompleteExtender1" runat="server" FirstRowSelected = "false">
</cc1:AutoCompleteExtender>
   
                  </div>

cs -View Code 

namespace:

using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using System.Collections.Generic;
using System.Data.SqlClient;
using System.Web.Services;

source Code

  [System.Web.Services.WebMethodAttribute(), System.Web.Script.Services.ScriptMethodAttribute()]
  
    public static List<string> Akramsrch(string prefixText, int count)
    {
        SqlConnection con = new SqlConnection("server=SOFTNET-AKRAM;database=zizlee;uid=sa;pwd=12345;");
       
       {
      
            using (SqlCommand cmd = new SqlCommand())
            {
                cmd.CommandText = "select City_Name from dbo.G_Service_Area where " +
                "City_Name like @SearchText + '%'";
                cmd.Parameters.AddWithValue("@SearchText", prefixText);
                cmd.Connection = con;
                con.Open();
                List<string> customers = new List<string>();
                using (SqlDataReader sdr = cmd.ExecuteReader())
                {
                    while (sdr.Read())
                    {
                        customers.Add(sdr["City_Name"].ToString());
                    }
                }
              
                return customers;
            }

        }
     

    }