private void AddDummyItem()
        {
            var item = new ScalarExpressionItem(true)
            {
                Location = new Point(0, _items.Count * ArrayExpressionItem.ItemHeight - VerticalScroll.Value),
                Width    = Width
            };

            item.textBox1.KeyPress += DummyItemNameKeyPress;
            _items.Add(item);
            item.Anchor |= AnchorStyles.Right;
            Controls.Add(item);
        }
 private void MakeNotDummy(ScalarExpressionItem di)
 {
     di.textBox1.KeyPress -= DummyItemNameKeyPress;
     di.MakeNotDummy();
     AddDummyItem();
 }