ARCed.Database.Items.ItemMainForm.CheckGroupBoxElementsOnCheckChange C# (CSharp) Method

        private void CheckGroupBoxElementsOnCheckChange(object sender, ItemCheckEventArgs e)
        {
            if (SuppressEvents) return;
            var id = e.Index + 1;
            if (e.NewValue == CheckState.Checked && !this._item.element_set.Contains(id))
                this._item.element_set.Add(id);
            else if (e.NewValue == CheckState.Unchecked && this._item.element_set.Contains(id))
                this._item.element_set.Remove(id);
        }