Form1

        private void button1_Click(object sender, EventArgs e)
        {
            Form f = new Form2(ref listView1);
            f.Activate();
            f.Show();
        }


Form2

        private ListView lv;
        public Form2(ref ListView _lv)
        {
            this.lv = _lv;
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            ListViewItem lvi = new ListViewItem();

            lvi.SubItems.Add("1");
            lvi.SubItems.Add("2");
            lvi.SubItems.Add("3");

            lv.Items.Add(lvi);
        }