private void listBox1_SelectedIndexChanged(object sender, EventArgs e) { listBox2.Items.Clear(); if (!int.TryParse(listBox1.GetItemText(listBox1.SelectedItem), out int id)) { Console.WriteLine("{0} is not an integer", id); } else { id = Convert.ToInt32(listBox1.GetItemText(listBox1.SelectedItem)); } Train.AddWagonAnimal(listBox2, id); }