What is BuildContext and what are its pitfalls?

BuildContext is implemented by Element. Calling Theme.of or MediaQuery.of registers a dependency on an InheritedWidget, so the widget rebuilds when that data changes. Navigator.of, ScaffoldMessenger.of and GoRouter.of use the same lookup mechanism.

Future<void> openProfile(BuildContext context) async {
  final theme = Theme.of(context);
  final navigator = Navigator.of(context);
  final profile = await api.fetchProfile();

  if (!context.mounted) return;
  navigator.push(
    MaterialPageRoute(builder: (_) => ProfilePage(profile: profile)),
  );
  debugPrint(theme.colorScheme.primary.toString());
}

• Look up dependencies in build or didChangeDependencies, not in initState
• After an await, check context.mounted before using the context
• Capture Navigator or ScaffoldMessenger before the await when appropriate
• Never store a BuildContext in a long-lived object
• A context above MaterialApp cannot find a Navigator or Theme from below it

Why context can become invalid

When a route is popped or a widget is removed, its element is deactivated. Calling an inherited lookup with that context throws or returns stale results. The mounted check prevents the common use-after-dispose failure after async navigation.