我不能在 ObservableCollection 上使用 Filter 方法

Question

On my viewModel I developed this code that will allow me to implement a research filter:

        public ICollection<Nc> Ncs
        {
            get
            {
                var ncs = _ncManager.Ncs;

                _ncCollectionView = CollectionViewSource.GetDefaultView(ncs);
                _ncCollectionView.Filter = _DoesNcMatchFileNameFilter;

                return ncs;
            }
        }
        private ICollectionView _ncCollectionView;

This method works, but if I try to implement another similar method in another viewModel :

    private ObservableCollection<Material> _materials;
    public ObservableCollection<Material> materials
    {
       get
       {
          var materials = Material.Name;
          _materialCollectionView = (CollectionViewSource)CollectionViewSource.GetDefaultView(materials);
          _materialCollectionView.Filter = _DoesMaterialMatchFileNameFilter;
    
          return Materials;
       }
    }
    private CollectionViewSource _materialCollectionView;

I get an error: CollectionViewSrouce.Filter can only appear on the left hand side of += or -=".

Why can't I do the same thing? What did I do wrong?

I've tried to read this page ObservableCollection<> vs. List<> but it didn't help me.

Answer 1

should _materialCollectionView not be of type ICollectionView ?

So:

private ObservableCollection<Material> _materials;
    public ObservableCollection<Material> materials
    {
       get
       {
          var materials = Material.Name;
          _materialCollectionView = CollectionViewSource.GetDefaultView(materials);
          _materialCollectionView.Filter = _DoesMaterialMatchFileNameFilter;
    
          return Materials;
       }
    }
    private ICollectionView _materialCollectionView;