public partial class Form1 : Form
    {
        public List<string> sys_directory = new List<string>();
        public List<string> sys_extension = new List<string>();

        public Form1()
        {
            InitializeComponent();            

            HelperClass h = new HelperClass();
            h.Run();    
        }
        
        private void OnNewListItem(object source, EventArgs e)
        {
            DataGridView1.DataSource = ...
        }
    }