ProviderObserver

ProviderObserver listens to the changes of a ProviderContainer.

To use it, extend the class ProviderObserver and override the method you like to use.

didAddProvider is called every time a provider was initialized, and the value exposed is value.
didDisposeProvider is called every time A provider was disposed
didUpdateProvider is called every time my providers when they emit a notification.
mayHaveChanged is called when the dependency of a provider changed, but it is not yet sure if the computed value changes.

info

It is possible that mayHaveChanged will be called, without didUpdateProvider being called, such as when a Provider is re-computed but returns a value == to the previous one.

Usage :

A simple use case for ProviderObserver, is to log the changes in providers by overriding the method didUpdateProvider.

// A Counter example implemented with riverpod with Logger

class Logger extends ProviderObserver {
  @override
  void didUpdateProvider(
    ProviderBase provider,
    Object? previousValue,
    Object? newValue,
    ProviderContainer container,
  ) {
    print('''
{
  "provider": "${provider.name ?? provider.runtimeType}",
  "newValue": "$newValue"
}''');
  }
}

void main() {
  runApp(
    // Adding ProviderScope enables Riverpod for the entire project
    // Adding our Logger to the list of observers
    ProviderScope(observers: [Logger()], child: MyApp()),
  );
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(home: Home());
  }
}

final counterProvider = StateProvider((ref) => 0);

class Home extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Counter example')),
      body: Center(
        child: Consumer(builder: (context, ref, _) {
          final count = ref.watch(counterProvider).state;
          return Text('$count');
        }),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () => context.read(counterProvider).state++,
        child: const Icon(Icons.add),
      ),
    );
  }
}

Now that every time the value of our provider is updated, the logger will log it :

I/flutter (16783): {
I/flutter (16783):   "provider": "counter",
I/flutter (16783):   "newValue": "Instance of 'StateController<int>'"
I/flutter (16783): }

info

Usage :​

Usage :