Does EnableCollectionSynchronization also require locking use of the ICollectionView?

Question

I am familiar with BindingOperations.EnableCollectionSynchronization to make WPF participate in locking access to an ObservableCollection for use on multiple threads.

But does this place the same restriction on my use of a CollectionViewSource.View that uses that ObservableCollection as its source? Or does the view contain its own internal list?

For example, consider the following simplified view-model (which I admit I have not compiled) with a protected list of shapes that is publicly exposed from a CollectionViewSource view. As long as I protect every use of the _shapes collection with the _lock object, I should be fine and WPF will like me.

But should I be locking the same _lock object in the DoesViewContainShape function?

public class MeasureVm
{
    public MeasureVm()
    {
        BindingOperations.EnableCollectionSynchronization(_shapes, _lock);  
        _cvsShapes = new CollectionViewSource() { Source = _shapes, Filter = FilterShapes };
    }

    // WPF Binds to this

    public ICollectionView Shapes => _cvsShapes.View;

    private  bool FilterShapes(object obj)
    {
         // Eventually some arbitrary code to filter out shapes
         return true.
    }
    public void AddShape(shape)
    {
        // Any use of _shapes requires locking.

        lock(_lock)
            _shapes.Add(shape);
    }

    public bool DoesViewContainShape(Shape shape)
    {
        // SHOULD I LOCK HERE?
        return _cvsShapes.View.Contains(shape);
    }

    private ObservableCollection<Shape> _shapes = new();
    private CollectionViewSource _cvsShapes;
    private object _lock                        = new();

}

Answer 1

You are confusing the ICollectionView interface (https://learn.microsoft.com/ru-ru/dotnet/api/system.componentmodel.icollectionview?view=windowsdesktop-8.0) with its implementation, the CollectionView class (https://learn.microsoft.com/en-us/dotnet/api/system.windows.data.collectionview?view=windowsdesktop-8.0). The ICollectionView interface does not impose restrictions on multithreading. The CollectionView class is derived from DispatcherObject, which itself ensures its thread safety, but also makes it single-threaded (in the thread that created it).

P.S.

I was simply noting that the only thing that I get from CollectionViewSource.View is the interface. Is that always implemented by an instance of the CollectionView class? Is that guaranteed?

In default implementations, the CollectionViewSource.View property will always return a class derived from CollectionView. But if desired, you can replace it with your own custom implementation of ICollectionView, which will not be derived from CollectionView. Although this is not excluded, but in all my practice, I have not encountered such a solution.
For "replacement", it is necessary that the source implements the ICollectionViewFactory Interface.