majiayu000 Riverpod — Containers / Scopes
Instructions
Providers themselves hold no state. State is stored in a ProviderContainer. In Flutter you use the ProviderScope widget, which creates and exposes a container to the widget tree.
Flutter: ProviderScope
Wrap your app at the root so widgets can read providers:
void main() {
runApp(
ProviderScope(
child: MyApp(),
),
);
}
After that, use Consumer / ConsumerWidget / ConsumerStatefulWidget to get a ref and call ref.watch / ref.read. You can also pass overrides or observers to ProviderScope.
Pure Dart: ProviderContainer
In command-line or server-side Dart, create a container, use it, then dispose it:
void main() {
final container = ProviderContainer();
try {
final sub = container.listen(counterProvider, (previous, next) {
print('Counter changed from $previous to $next');
});
print('Counter starts at ${sub.read()}');
} finally {
container.dispose();
}
}
Why state lives in a container
- Separation of concerns — Only the provider (and ref) can change its state; the UI typically calls notifier methods.
- Testing — Each test can create a new container (e.g.
ProviderContainer.test()) for a fresh state; no shared global state. - Configuration — Overrides and observers are set on the container/scope. See riverpod-overrides and riverpod-observers.
- Scoping — The same provider can resolve to different state in different parts of the tree (advanced). See riverpod-scoping.
Testing
Do not use ProviderContainer() directly in tests. Use ProviderContainer.test() so the container is disposed when the test ends:
test('Counter starts at 0 and can be incremented', () {
final container = ProviderContainer.test();
expect(container.read(counterProvider), 0);
container.read(counterProvider.notifier).increment();
expect(container.read(counterProvider), 1);
});
In widget tests, wrap the widget in ProviderScope and use tester.container() to get the container if needed (see riverpod-testing).