How to write a public function when use Enum parameter?

        public static void SetStringAlignment(ref StringAlignment aStringAlignment, DropDownList dropDownAlignment, bool isUpdateControls)
        {
            if (isUpdateControls == true)
            {
                dropDownAlignment.SelectedIndex = dropDownAlignment.Items.IndexOf(new ListItem(aStringAlignment.ToString()));
            }
            else
            {
                aStringAlignment = (StringAlignment)Enum.Parse(typeof(StringAlignment) ...