ObservableCollection CollectionChanged

Есть коллекция

public MvxObservableCollection<Note> Notes = new MvxObservableCollection<Note>(await App.DataBase.GetItemsAsync());
Notes.CollectionChanged += OnCollectionChanged;

При добавлении элемента Notes.Add(item); не вызывается метод OnCollectionChanged

void OnCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
    {

        if (e.NewItems != null)
        {
            foreach (Note newItem in e.NewItems)
            {
                newItem.ActionSheetEventHandler += ActionSheetExecute;
            }
        }
        if (e.Action == NotifyCollectionChangedAction.Remove)
            if (e.OldItems != null)
            {
                foreach (Note oldItem in e.OldItems)
                {
                    oldItem.ActionSheetEventHandler -= ActionSheetExecute;
                }

            }
    }