public ProjectItem Item(object index)
        {
            if (!(index is int number))
            {
                return(null);
            }
            var itemModel = ProjectItemModels.ElementAtOrDefault(number);

            if (itemModel == null)
            {
                return(null);
            }
            return(new ProjectItemImplementation(Implementation, itemModel));
        }
 public IEnumerator GetEnumerator() =>
 ProjectItemModels.Select(model => new ProjectItemImplementation(Implementation, model)).GetEnumerator();