How to develop AutoComplete Text in windows Textbox using C#.Net?

AutoCompleteStringCollection namesCollection = new AutoCompleteStringCollection();

SqlDataReader dReader;
SqlConnection con = new SqlConnection("Data Source=idiot;Initial Catalog=INDIA;User ID=sa;Password=12345");
SqlCommand cmd = new SqlCommand();
cmd.Connection = con;
cmd.CommandType = CommandType.Text;
cmd.CommandText = "select givenname from patient";
con.Open();
dReader = cmd.ExecuteReader();
if (dReader.HasRows == true)
{
while (dReader.Read())
namesCollection.Add(dReader["givenname"].ToString());

}
else
{
MessageBox.Show("Data not found");
}
dReader.Close();

textBox1.AutoCompleteMode = AutoCompleteMode.Suggest;
textBox1.AutoCompleteSource = AutoCompleteSource.CustomSource;
textBox1.AutoCompleteCustomSource = namesCollection;