how to use autocomplete in asp net

Use Below Code to show data in Textbox in Asp.net :

<System.Web.Script.Services.ScriptMethod(), System.Web.Services.WebMethod()>
Public Shared Function SearchUnit(ByVal prefixText As String, ByVal count As Integer) As List(Of String) 
Dim con As SqlConnection = New SqlConnection 
con.ConnectionString = ConfigurationManager.ConnectionStrings("MTechSqlDatabaseConnectionString").ConnectionString Dim cmd As SqlCommand = New SqlCommand 
cmd.CommandText = String.Format("select UnitType from UnitType where UnitType LIKE '%{0}%' ", prefixText) ' 
cmd.Parameters.AddWithValue("@ProductName", prefixText) 
cmd.Connection = con 
con.Open()
Dim UnitType As List(Of String) = New List(Of String) 
Dim sdr As SqlDataReader = cmd.ExecuteReader 
While sdr.Read 
UnitType.Add(sdr("UnitType").ToString) 
End While 
con.Close() 
Return UnitType 
End Function



<div> <asp:ScriptManager ID="ScriptManager1" runat="server" EnablePageMethods="True"></asp:ScriptManager> <asp:TextBox ID="TextBox4" runat="server"></asp:TextBox> <ajaxToolkit:AutoCompleteExtender ID="AutoCompleteExtender2" runat="server" CompletionInterval="100" EnableCaching="False" MinimumPrefixLength="1" ServiceMethod="SearchUnit" TargetControlID="TextBox4"></ajaxToolkit:AutoCompleteExtender> </div>