private void selectItemsToolStripMenuItem_Click(object sender, EventArgs e)
        {
            SelectItemForm sif = new SelectItemForm(_superList);

            if (sif.ShowDialog(this) == DialogResult.OK)
            {
                _superList.SelectedItems.AddRange(sif.SelectedItems);
            }
        }
        private void _ensureItemVisibleToolStripMenuItem_Click(object sender, EventArgs e)
        {
            SelectItemForm sif = new SelectItemForm(_superList);

            if (sif.ShowDialog(this) == DialogResult.OK && sif.SelectedItems.Length > 0)
            {
                MessageBox.Show(this, sif.SelectedItems[0].ToString());
                _superList.FocusedItem = sif.SelectedItems[0];
            }
        }