ProviderObservers

A ProviderObserver is an object used to observe provider lifecycle events in the application. They are generally used for logging, analytics, or debugging purposes.

Usage

To use a ProviderObserver, you need to extend the class and override the life-cycles you want to observe. There are many methods available. It is recommended to check its documentation for more details.

Example: Logger

The following observer logs all state changes of any provider in the application:

// A basic logger, which logs any state changes.
class Logger extends ProviderObserver {
  @override
  void didUpdateProvider(
    ProviderObserverContext context,
    Object? previousValue,
    Object? newValue,
  ) {
    print('''
{
  "provider": "${context.provider}",
  "newValue": "$newValue",
  "mutation": "${context.mutation}"
}''');
  }
}

void main() {
  runApp(
    ProviderScope(
      // ProviderObservers are used by passing them to ProviderScope/ProviderContainer
      observers: [
        // Adding ProviderScope enables Riverpod for the entire project
        // Adding our Logger to the list of observers
        Logger(),
      ],
      child: const MyApp(),
    ),
  );
}

// After this, implement a typical Flutter application

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

{
  "provider": "Provider<int>",
  "newValue": "1"
}

To improve debugging, you can optionally give your providers a name:

final myProvider = Provider<int>((ref) => 0, name: 'MyProvider');

With this change, the log becomes:

{
  "provider": "MyProvider",
  "newValue": "1"
}

astuce

When using code-generation, a name is automatically assigned to providers.

remarque

If the state of a provider is mutated, (typically Lists, combined with Ref.notifyListeners), it is likely that didUpdateProvider will receive previousValue and newValue as the same value.

This happens because Dart updates objects by "reference". If you want to change this, you will have to clone your objects before mutating them.