unoplatform/uno · error · InvalidOperationException

Activity must provide lifecycle events.

Error message

Activity must provide lifecycle events.

What it means

Thrown by the FoldableApplicationViewSpanningRects constructor when ViewManagement.ApplicationViewHelper.GetActivityLifecycleEvents() returns null. This class relies on the host Activity implementing/exposing Jetpack Window Manager lifecycle hooks (Create, Start, Stop). If the activity does not provide lifecycle events (the helper has no registered lifecycle source), the foldable spanning-rects feature cannot function.

Source

Thrown at src/AddIns/Uno.UI.Foldable/FoldableApplicationViewSpanningRects.Android.cs:40

	/// and exposing the properties needed to make UI change when required.
	/// FUTURE: implement an event for layout changes, so we can respond to folding state changes in app code too
	/// </remarks>
	[Preserve]
	public partial class FoldableApplicationViewSpanningRects : IApplicationViewSpanningRects, INativeDualScreenProvider
	{
		private (SurfaceOrientation orientation, List<Rect> result) _previousMode = EmptyMode;

		private static readonly (SurfaceOrientation orientation, List<Rect> result) EmptyMode =
			((SurfaceOrientation)(-1), null);

		private readonly List<Rect> _emptyList = new List<Rect>(0);

		public FoldableApplicationViewSpanningRects(object owner)
		{
			var lifecycleEvents = ViewManagement.ApplicationViewHelper.GetActivityLifecycleEvents();
			if (lifecycleEvents is null)
			{
				throw new InvalidOperationException("Activity must provide lifecycle events.");
			}

			lifecycleEvents.Create += OnCreateEvent;
			lifecycleEvents.Start += OnStartEvent;
			lifecycleEvents.Stop += OnStopEvent;
		}

		private void OnCreateEvent(object sender, Android.OS.Bundle savedInstanceState)
		{
			windowInfoTrackerCallbackAdapter = new WindowInfoTrackerCallbackAdapter(WindowInfoTracker.Companion.GetOrCreate(ContextHelper.Current as Android.App.Activity));
			windowMetricsCalculator = WindowMetricsCalculator.Companion.OrCreate; // HACK: source method is `getOrCreate`, binding generator munges this badly :(
			if (this.Log().IsEnabled(LogLevel.Debug))
			{
				this.Log().Debug($"DualMode: FoldableApplicationViewSpanningRects.OnCreateEvent");
			}
		}
		private void OnStartEvent(object sender, EventArgs args)
		{

View on GitHub (pinned to 0418340488)

Solutions

1. Ensure the app's MainActivity is configured to provide lifecycle events to ApplicationViewHelper (register the activity lifecycle events source at startup).
2. Guard construction of FoldableApplicationViewSpanningRects with a check that GetActivityLifecycleEvents is non-null, or only instantiate it on devices that report a hinge/fold.
3. Verify the Uno.UI.Foldable NuGet add-in is correctly wired and the activity implements the expected interface.

Example fix

// before: construct unconditionally
var spanning = new FoldableApplicationViewSpanningRects(this); // throws if no lifecycle events

// after: guard before construction
if (ViewManagement.ApplicationViewHelper.GetActivityLifecycleEvents() is not null)
{
    var spanning = new FoldableApplicationViewSpanningRects(this);
}

// Before constructing, verify lifecycle events are available
var lifecycle = ViewManagement.ApplicationViewHelper.GetActivityLifecycleEvents();
if (lifecycle is not null)
{
    var spanning = new FoldableApplicationViewSpanningRects(this);
}

try {
    var spanning = new FoldableApplicationViewSpanningRects(this);
} catch (InvalidOperationException ex) when (ex.Message.Contains('lifecycle events')) {
    // Activity does not provide lifecycle events — skip foldable feature
}

When it happens

Trigger: Constructing FoldableApplicationViewSpanningRects when the current Activity has not registered with ApplicationViewHelper for lifecycle events, or the app's MainActivity does not implement the required lifecycle interface for the Uno foldable add-in.

Common situations: Using the Uno.UI.Foldable add-in without configuring the MainActivity to provide lifecycle events; the add-in is loaded in a context (e.g. a non-Activity host, a test harness) where GetActivityLifecycleEvents returns null; running on a non-foldable device where the foldable add-in is still initialized.

Related errors

• FoldableHingeAngleSensor must be initialized on the UI Threa
• Value cannot be null. (Parameter 'storeContext')
• A DragDropExtension has already been enabled
• The current DragDropExtension does not match the provided ar
• No pending drag and drop data.

AI-assisted analysis of unoplatform/uno@0418340488 (2026-08-13). Data as JSON: /api/errors/7f63e9204031859b. Report an issue: GitHub.