public virtual void RemoveItem(DataViewModel viewmodel)
        {
            if (SelectedItem == viewmodel)
            {
                SelectedItem = null;
            }

            Items.Remove(viewmodel);
        }
        public virtual void OnSourceCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
        {
            if (e.NewItems != null && e.NewItems.Count > 0)
            {
                foreach (DataModel model in e.NewItems)
                {
                    Items.Add(NewItem(model));
                }
            }

            if (e.OldItems != null && e.OldItems.Count > 0)
            {
                foreach (DataModel model in e.OldItems)
                {
                    DataViewModel viewmodel = FindByID(model.ID);
                    if (viewmodel != null)
                    {
                        RemoveItem(viewmodel);
                    }
                }
            }
        }