dotnet/wpf · error · InvalidOperationException

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

Error message

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

What it means

ListCollectionView.AddNew is only legal when CanAddNew is true — i.e. the underlying collection supports adding (IBindingList/AddNew semantics or the collection is not read-only/fixed-size) and any AddNew transaction limit is respected. Otherwise it throws InvalidOperationException with MemberNotAllowedForView("AddNew").

Solutions

  1. Check CanAddNew before calling AddNew and disable the Add UI when it is false
  2. Make the underlying collection writable: use a List<T>/ObservableCollection<T> instead of a read-only or fixed-size list
  3. Provide a public parameterless constructor (or NewItemFactory) for the item type so the view can create instances

Example fix

// before
var newItem = (MyItem)view.AddNew(); // throws on read-only source
// after
if (((IEditableCollectionView)view).CanAddNew)
{
    var newItem = (MyItem)view.AddNew();
}
else { /* disable add UI */ }
Defensive patterns

Strategy: validation

Validate before calling

var ecv = (IEditableCollectionView)view;
if (ecv.CanAddNew)
{
    var item = ecv.AddNew();
}
else { /* disable add feature or use a writable collection */ }

Try / catch

try { var item = view.AddNew(); }
catch (InvalidOperationException)
{
    // underlying collection does not support adding; surface to user
}

Prevention

When it happens

Trigger: Calling AddNew() when the underlying IList is read-only or fixed-size, when a NewItemFactory/constructor is unavailable for the item type, or when the collection does not permit new items (CanAddNew false).

Common situations: DataGrid 'add row' feature bound to a read-only collection (e.g. a computed/frozen list, an array, or a list exposed without setters); MVVM code calling AddNew on views over immutable data.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/378d3cc5f81c9f72. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Data/ListCollectionView.cs:716

        /// <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"));

            return AddNewCommon(_itemConstructor.Invoke(null));
        }

        /// <summary>
        /// Add a new item to the underlying collection.  Returns the new item.
        /// After calling AddNewItem 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 AddNewItem(object newItem)
        {
            VerifyRefreshNotDeferred();

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

View on GitHub (pinned to 81131a70a4)