I use auto complete Extender just the way you do.. here take a look on code:
aspx page:
<asp:AutoCompleteExtender ID="TextBox1_AutoCompleteExtender" runat="server"
CompletionInterval="10" CompletionSetCount="10" DelimiterCharacters=""
Enabled="True" FirstRowSelected="true" MinimumPrefixLength="1"
ServiceMethod="GetName" TargetControlID="TextBox1" UseContextKey="true">
aspx.cs code:
[System.Web.Services.WebMethod]
[System.Web.Script.Services.ScriptMethod]
public static List<string> GetName(string prefixText, int count)
{
if (count == 0)
{
count = 5;
}
SqlConnection conn = new SqlConnection();
conn.ConnectionString = <connectionstring>;
SqlCommand cmd = new SqlCommand(sqlquery, conn);
conn.Open();
List<string> names = new List<string>();
SqlDataReader dr = cmd.ExecuteReader();
while (dr.Read())
{
names.Add(dr[<columnname>].ToString());
}
conn.Close();
return names;
}</columnname></connectionstring>
lemme know if it was what you were looking for.