private void buttonGetFields_Click(object sender, EventArgs e)
{
   //autocomplete for comboBoxColumns
   AutoCompleteStringCollection autoCompleteSource1 = new AutoCompleteStringCollection();
   comboBoxColumns.AutoCompleteSource = AutoCompleteSource.CustomSource;
    foreach (string tempStr in comboBoxColumns.Items)
            autoCompleteSource1.Add(tempStr);
    comboBoxColumns.AutoCompleteCustomSource = autoCompleteSource1;
    comboBoxColumns.AutoCompleteMode = AutoCompleteMode.SuggestAppend;
}