iOS: RenderBox was not laid out — unguarded currentContext?.size in async onPlatformViewCreated becomes an uncatchable fatal (2.18.0-2.28.0)

[luis-calupet]

On iOS, _MapWidgetState.onPlatformViewCreated reads key.currentContext?.size while the platform view can be mounted but not yet laid out. Element.size throws RenderBox was not laid out in that state — the ?. only guards a null context, not an unlaid-out element. Because onPlatformViewCreated is async with no await before the read, the synchronous throw is captured into a Future that DarwinViewState._createNewUiKitView discards along with its try/catch — so the error surfaces as an unhandled-zone fatal that no app-side try/catch can intercept, with zero app frames in the trace.

Affected code

lib/src/map_widget.dart — present at least from 2.18.0 (line 329) through 2.23.0 (line 337) and still unguarded in 2.28.0 (line 350):

Future<void> onPlatformViewCreated(int id) async {
  ...
  // WARNING: Because platform view is not sized at this moment on iOS,
  // it is not safe to call methods that depend on the size of the platform view,
  ...
  final size = key.currentContext?.size;   // <-- throws when mounted but not laid out
  if (size != null) {
    await _mapboxMapsPlatform.submitViewSizeHint(
        width: size.width, height: size.height);
  }
  ...
}

The method's own WARNING comment already states the view is not sized at this moment — but Element.size on a render box whose layout has not completed does not return null; it throws.

Reproduction shape

A MapWidget mounts while a route transition is still in flight (e.g. a screen containing the map is pushed and the platform view is created before first layout of the new route completes). We see this in production crash reporting (Sentry) as level: fatal, RenderBox was not laid out, with no application frames — which is exactly the discarded-Future mechanism above. 7 events / 5 distinct users on our iOS build over ~1 week, reproducing across app versions.

Suggested fix

Any of:

• guard the read: final ctx = key.currentContext; final box = ctx?.findRenderObject(); final size = (box is RenderBox && box.hasSize) ? box.size : null;
• defer the size-hint to a post-frame callback when layout hasn't completed;
• or make the read part of an awaited chain so a failure is at least observable/handleable rather than an unhandled zone error.

The size hint is an optimization, so a null/deferred fallback is safe — considerably safer than an uncatchable fatal.