AvaloniaUI/Avalonia · error · NotSupportedException

Collection reset not supported.

Error message

Collection reset not supported.

What it means

NotSupportedException ('Collection reset not supported.') thrown by AvaloniaListExtensions.TrackItemPropertyChanged when the observed collection raises a Reset event. By design TrackItemPropertyChanged wires a throwing delegate as the reset handler because it cannot safely re-subscribe property-changed handlers after a wholesale reset, so resets are explicitly unsupported.

Source

Thrown at src/Avalonia.Base/Collections/AvaloniaListExtensions.cs:197

                    var inpc = x as INotifyPropertyChanged;

                    if (inpc != null)
                    {
                        inpc.PropertyChanged += handler;
                        tracked.Add(inpc);
                    }
                },
                x =>
                {
                    var inpc = x as INotifyPropertyChanged;

                    if (inpc != null)
                    {
                        inpc.PropertyChanged -= handler;
                        tracked.Remove(inpc);
                    }
                },
                () => throw new NotSupportedException("Collection reset not supported."));

            return Disposable.Create(() =>
            {
                foreach (var i in tracked)
                {
                    i.PropertyChanged -= handler;
                }
            });
        }
    }
}

View on GitHub (pinned to 11c5427268)

Solutions

1. Avoid Reset on the tracked collection — remove items individually instead of calling Clear().
2. Dispose the TrackItemPropertyChanged subscription before reloading and re-create it afterward.
3. Replace wholesale Clear() with a Remove-based teardown so Reset is never raised.

Example fix

// before
using var sub = items.TrackItemPropertyChanged(OnItemChanged);
items.Clear(); // raises Reset -> throws

// after
sub.Dispose();
items.Clear();
using var sub2 = items.TrackItemPropertyChanged(OnItemChanged);

sub.Dispose();
collection.Clear();
sub = collection.TrackItemPropertyChanged(callback);

When it happens

Trigger: Calling collection.TrackItemPropertyChanged(callback) on a list that subsequently raises NotifyCollectionChangedAction.Reset (Clear, reload, filter change).

Common situations: Tracking PropertyChanged on items in a collection that gets cleared or rebuilt (data refresh, navigation, filtering); ObservableCollection<T>.Clear() which raises Reset.

Related errors

• Reset called on collection without reset handler.
• Reset called on collection without reset handler.
• items
• array
• Multi-dimensional arrays are not supported.

AI-assisted analysis of AvaloniaUI/Avalonia@11c5427268 (2026-08-13). Data as JSON: /api/errors/1830d9df77667b7d. Report an issue: GitHub.