void LoadSubscribe(IEnumerable<object> enumerator, ItemCheckedEventHandler action)
        {
            listView1.Visible = false;
            listView1.CheckBoxes = true;
            //if (action != null)//1  ВАРИАНТ КАК У ВАС
            //{
            //    listView1.ItemChecked += action;
            //}
            foreach (var v in from object v in (IEnumerable)enumerator let item = new ListViewItem(v.ToString()) { Checked = true } select v)
                listView1.Items.Add(new ListViewItem(v.ToString()) { Checked = true });
            if (action != null)// ПРЕДЛАГАЮ Я
            {
                listView1.ItemChecked += action;
            }
            listView1.Visible = true;
        }

  LoadSubscribe(Enumerable.Range(1,20).Cast<object>(),(o, args) => { MessageBox.Show("sd"); }); // вызов