dotnet/wpf · error · InvalidOperationException

SR.Format(SR.MemberNotAllowedForView, "AddNew")

Error message

SR.Format(SR.MemberNotAllowedForView, "AddNew")

What it means

BindingListCollectionView.AddNew() throws this InvalidOperationException when the view does not currently permit adding a new item. AddNew first implicitly closes any pending CommitEdit/CommitNew transactions, then checks the CanAddNew flag; if the bound collection is not IBindingList with AllowNew support (or filtering/sorting state makes a new item unplaceable), the operation is rejected.

Solutions

  1. Check the view's CanAddNew property before calling AddNew and disable/redirect the Add action when false.
  2. Use a source collection implementing IBindingList with AllowNew == true (e.g. BindingList<T> or a DataView).
  3. Clear any active EditItem/AddNew transaction first; a pending transaction is implicitly closed, but the view may still report CanAddNew false due to filter state.
  4. If a filter is active, verify your filter allows the position where the new item would be inserted, or remove the filter before adding.

Example fix

// before
((BindingListCollectionView)view).AddNew();

// after
var blcv = (BindingListCollectionView)view;
if (!blcv.CanAddNew) throw new NotSupportedException("Collection does not allow adding.");
blcv.AddNew();
Defensive patterns

Strategy: validation

Validate before calling

// C#
var blcv = view as BindingListCollectionView;
if (blcv == null || !blcv.CanAddNew) throw new InvalidOperationException("Cannot add new item on this view.");

Type guard

bool CanAddSafely(ICollectionView v) => v is BindingListCollectionView b && b.CanAddNew;

Prevention

When it happens

Trigger: Calling AddNew() on a BindingListCollectionView whose source collection is not IBindingList, whose AllowNew property is false, or whose custom CanAddNew logic (e.g. AddNew canPlaceNewItem filter) returns false.

Common situations: Binding an ItemsControl to a plain List<T> or ObservableCollection<T> (not BindingList<T>) and calling AddNew from an 'Add' button; a DataGrid in edit mode issuing implicit AddNew; a filter predicate rejecting the placeholder position for a new item.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/2afb6f00c5004198. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Data/BindingListCollectionView.cs:569

        /// <summary>
        /// Add a new item to the underlying collection.  Returns the new item.
        /// After calling AddNew and changing the new item as desired, either
        /// <seealso cref="CommitNew"/> or <seealso cref="CancelNew"/> should be
        /// called to complete the transaction.
        /// </summary>
        public object AddNew()
        {
            VerifyRefreshNotDeferred();

            if (IsEditingItem)
            {
                CommitEdit();   // implicitly close a previous EditItem
            }

            CommitNew();        // implicitly close a previous AddNew

            if (!CanAddNew)
                throw new InvalidOperationException(SR.Format(SR.MemberNotAllowedForView, "AddNew"));

            object newItem = null;
            BindingOperations.AccessCollection(InternalList,
                () =>
                {
                    ProcessPendingChanges();

                    _newItemIndex = -2; // this is a signal that the next ItemAdded event comes from AddNew
                    newItem = InternalList.AddNew();
                },
                true);

            Debug.Assert(_newItemIndex != -2 && newItem == _newItem, "AddNew did not raise expected events");

            MoveCurrentTo(newItem);

            ISupportInitialize isi = newItem as ISupportInitialize;
            isi?.BeginInit();

View on GitHub (pinned to 81131a70a4)