autocomplete textbox using ajax in asp.net

• First register the Ajax control toolkit in .aspx page like below.

          <%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit"

           TagPrefix="cc1" %>

• Put the ToolkitScriptManager from Ajax Control Toolkit in .aspx page.

        <cc1:ToolkitScriptManager ID="ToolkitScriptManager1" runat="server">
        </cc1:ToolkitScriptManager>

• Now assign the ajax control "AutoCompleteExtender" to theTextBox. 

          <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>

          <cc1:AutoCompleteExtender ID="AutoCompleteExtender1" runat="server"

                   TargetControlID="TextBox1" CompletionInterval="1000" 
                   MinimumPrefixLength="0" EnableCaching="True"
                   CompletionSetCount="1" ServiceMethod="GetCountries">

          </cc1:AutoCompleteExtender>

• Now create the service method for fetch data from database as per textbox requirement in .aspx.cs page.

          using System.Web.UI.WebControls;

          [System.Web.Services.WebMethod]

          public static List<string> GetCountries(string prefixText)
          { 

                SqlConnection con = new SqlConnection("connection string") ;

                con.Open();

                SqlDataAdapter da = new SqlDataAdapter("select * from tblCountry

                where CountryName like '" +  prefixText + "'+'%'", con);

                DataTable dt = new DataTable();

                da.Fill(dt);
                con.Close();

            

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

                for (int i = 0; i < dt.Rows.Count; i++)
                {
                        CountryNames.Add(dt.Rows[i][1].ToString());
                }
                return CountryNames;
          }