dotnet/wpf · error · InvalidOperationException

throw new InvalidOperationException(SR.RemovedItemNotFound);

Q: What causes "throw new InvalidOperationException(SR.RemovedItemNotFound);" in dotnet/wpf?

Fix the source collection to always set OldStartingIndex (and OldItems) when raising NotifyCollectionChangedAction.Remove.

Error message

throw new InvalidOperationException(SR.RemovedItemNotFound);

What it means

EnumerableCollectionView maintains an internal _snapshot of the source collection. On a Remove notification with no OldStartingIndex (index < 0), the view cannot locate which snapshot entry to remove, so it throws RemovedItemNotFound. This is an internal-invariant check: the INotifyCollectionChanged contract should always supply OldStartingIndex for Remove actions.

Solutions

Fix the source collection to always set OldStartingIndex (and OldItems) when raising NotifyCollectionChangedAction.Remove.
Raise NotifyCollectionChangedAction.Reset instead of an index-less Remove for bulk/unindexed changes.
Use ObservableCollection<T> (or a correct implementation) as the source instead of the custom collection.
Unbind/rebind (refresh the view) if the snapshot has already diverged.

Example fix

// before
RaiseCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Remove, item));
// after
int idx = IndexOf(item);
RaiseCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Remove, item, idx));

Defensive patterns

Strategy: validation

Validate before calling

// validate Remove args before raising
if (action == NotifyCollectionChangedAction.Remove && args.OldStartingIndex < 0)
    throw new InvalidOperationException("Remove events must supply OldStartingIndex");

Try / catch

// wrap view refresh
try { view.Refresh(); } catch (InvalidOperationException) { view.Refresh(); }

Prevention

Always set OldStartingIndex and OldItems on Remove events.
Prefer deriving custom collections from ObservableCollection<T>.
Use Reset for unindexed bulk removals.
Unit-test your INotifyCollectionChanged event payloads.

When it happens

Trigger: A source collection implementing INotifyCollectionChanged raises CollectionChanged with Action=Remove and OldStartingIndex = -1 (or omits the index), which EnumerableCollectionView processes via ProcessCollectionChanged.

Common situations: Using a custom or third-party ObservableCollection-like class that fires Reset-style Remove events with unspecified indices, violating the INotifyCollectionChanged contract while bound to an ItemsControl.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/ee8c7140c8a01127. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/MS/Internal/Data/EnumerableCollectionView.cs:420

                    if (args.NewStartingIndex < 0 || _snapshot.Count <= args.NewStartingIndex)
                    {   // append
                        for (int i = 0; i < args.NewItems.Count; ++i)
                        {
                            _snapshot.Add(args.NewItems[i]);
                        }
                    }
                    else
                    {   // insert
                        for (int i = args.NewItems.Count - 1; i >= 0; --i)
                        {
                            _snapshot.Insert(args.NewStartingIndex, args.NewItems[i]);
                        }
                    }
                    break;

                case NotifyCollectionChangedAction.Remove:
                    if (args.OldStartingIndex < 0)
                        throw new InvalidOperationException(SR.RemovedItemNotFound);

                    for (int i = args.OldItems.Count - 1, index = args.OldStartingIndex + i; i >= 0; --i, --index)
                    {
                        if (!System.Windows.Controls.ItemsControl.EqualsEx(args.OldItems[i], _snapshot[index]))
                            // replace error message with a better one
                            throw new InvalidOperationException(SR.Format(SR.AddedItemNotAtIndex, index));
                        _snapshot.RemoveAt(index);
                    }
                    break;

                case NotifyCollectionChangedAction.Replace:
                    for (int i = args.NewItems.Count - 1, index = args.NewStartingIndex + i; i >= 0; --i, --index)
                    {
                        if (!System.Windows.Controls.ItemsControl.EqualsEx(args.OldItems[i], _snapshot[index]))
                            // replace error message with a better one
                            throw new InvalidOperationException(SR.Format(SR.AddedItemNotAtIndex, index));
                        _snapshot[index] = args.NewItems[i];
                    }

View on GitHub (pinned to 81131a70a4)