private void AddInstance(ISymbolInstance symRef, bool add)
        {
            var li = new ListViewItem();

            li.Tag = symRef;

            SetListViewItemLabel(symRef, li);

            lstInstances.Items.Add(li);
            btnUp.Enabled = btnDown.Enabled = (lstInstances.Items.Count > 1);

            if (add)
            {
                _comp.AddSymbolInstance(symRef);
            }
            li.Selected = (lstInstances.Items.Count == 1);
            RenderPreview(symRef, li);
        }