dotnet/maui · error · ArgumentNullException

renderer

Error message

renderer

What it means

EventTracker constructor throws ArgumentNullException(nameof(renderer)) when the IVisualElementRenderer is null. EventTracker attaches gesture-recognizer collection-changed handling to a renderer's element; without a renderer there is no element to track, so construction is rejected immediately.

Solutions

1. Create EventTracker only after the renderer is fully initialized and assigned.
2. Verify the renderer is non-null before constructing EventTracker.
3. Move EventTracker initialization to OnElementChanged / the ElementChanged event.

Example fix

// before
_tracker = new EventTracker(null);
// after
if (renderer == null)
    throw new InvalidOperationException("Renderer not ready.");
_tracker = new EventTracker(renderer);

if (renderer == null)
    throw new InvalidOperationException("Renderer is not ready; cannot create EventTracker.");
var tracker = new EventTracker(renderer);

static bool IsRendererReady(IVisualElementRenderer r) => r?.Element != null;

When it happens

Trigger: Constructing EventTracker with a null renderer; typically only inside custom renderers that build an EventTracker before Platform.GetRenderer returns a value.

Common situations: A custom renderer instantiating EventTracker during constructor execution before the renderer is fully initialized; passing renderer from a GetRenderer call that returned null because the element was not registered.

Related errors

• application
• group
• indexPath
• indexPath
• renderer

AI-assisted analysis of dotnet/maui@f377ff1c5e (2026-08-13). Data as JSON: /api/errors/c793be0c583c4bc4. Report an issue: GitHub.

Appendix: source

Thrown at src/Compatibility/Core/src/iOS/EventTracker.cs:49

		readonly NotifyCollectionChangedEventHandler _collectionChangedHandler;

		readonly Dictionary<IGestureRecognizer, NativeGestureRecognizer> _gestureRecognizers = new Dictionary<IGestureRecognizer, NativeGestureRecognizer>();

		readonly IVisualElementRenderer _renderer;

		bool _disposed;
		NativeView _handler;

		double _previousScale = 1.0;
#if __MOBILE__
		UITouchEventArgs _shouldReceiveTouch;
		DragAndDropDelegate _dragAndDropDelegate;
#endif

		public EventTracker(IVisualElementRenderer renderer)
		{
			if (renderer == null)
				throw new ArgumentNullException(nameof(renderer));

			_collectionChangedHandler = ModelGestureRecognizersOnCollectionChanged;

			_renderer = renderer;
			_renderer.ElementChanged += OnElementChanged;
		}

		ObservableCollection<IGestureRecognizer> ElementGestureRecognizers
		{
			get
			{
				return ((_renderer?.Element as IGestureController)
							?.CompositeGestureRecognizers as ObservableCollection<IGestureRecognizer>);
			}
		}

		internal void Disconnect()
		{

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