dotnet/wpf · error · NotSupportedException

SR.RangeActionsNotSupported

Error message

SR.RangeActionsNotSupported

What it means

DocumentSequenceTextContainer._OnContentChanged handles CollectionChanged from the sequence's References. Add events must contain exactly one item; a multi-item (range) Add is not supported by the incremental ChildDocumentBlock bookkeeping, so NotSupportedException with RangeActionsNotSupported is thrown.

Solutions

  1. Add DocumentReference items one at a time so each Add event carries a single item
  2. Replace bulk AddRange with a loop of individual Add calls
  3. If you own the collection, never batch NotifyCollectionChangedAction.Add with multiple NewItems

Example fix

// before
references.AddRange(newDocs); // single Add event, count != 1
// after
foreach (var d in newDocs) { references.Add(d); }
Defensive patterns

Strategy: validation

Validate before calling

if (args.Action == NotifyCollectionChangedAction.Add && args.NewItems.Count != 1)
    throw new NotSupportedException("DocumentSequence.References supports single-item Add only");

Type guard

bool IsSingleItemAdd(NotifyCollectionChangedEventArgs a) => a.Action == NotifyCollectionChangedAction.Add && a.NewItems?.Count == 1;

Try / catch

try { references.AddRange(items); }
catch (NotSupportedException) { foreach (var i in items) references.Add(i); }

Prevention

When it happens

Trigger: Adding multiple DocumentReference items to DocumentSequence.References in one CollectionChanged event (e.g., AddRange or a collection that batches adds).

Common situations: Custom ObservableCollection subclass that raises one Add event with several new items; batch-loading child documents into a FixedDocumentSequence via a bulk-add helper.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/ca71593b407d5bff. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Documents/DocumentSequenceTextContainer.cs:595

            {
                textContainer.EndChange();
            }
        }

        //--------------------------------------------------------------------
        // ContentChange
        //---------------------------------------------------------------------
        private void _OnContentChanged(object sender, NotifyCollectionChangedEventArgs args)
        {
#if DEBUG
            this._generation++;
#endif

            if (args.Action == NotifyCollectionChangedAction.Add)
            {
                if (args.NewItems.Count != 1)
                {
                    throw new NotSupportedException(SR.RangeActionsNotSupported);
                }
                else
                {
                        object item = args.NewItems[0];
                        int startingIndex = args.NewStartingIndex;

                        if (startingIndex != _parent.References.Count - 1)
                        {
                            throw new NotSupportedException(SR.Format(SR.UnexpectedCollectionChangeAction, args.Action));
                        }

                        ChildDocumentBlock newBlock = new ChildDocumentBlock(this, (DocumentReference)item);

                        ChildDocumentBlock insertAfter = _doclistTail.PreviousBlock;
                        insertAfter.InsertNextBlock(newBlock);
                        DocumentSequenceTextPointer changeStart =
                            new DocumentSequenceTextPointer(insertAfter, insertAfter.End);

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