FutureProvider

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FutureProvider is the equivalent of Provider but for asynchronous code.

FutureProvider is typically used for:

performing and caching asynchronous operations (such as network requests)
nicely handling error/loading states of asynchronous operations
combining multiple asynchronous values into another value

FutureProvider gains a lot when combined with ref.watch. This combination allows automatic re-fetching of some data when some variables change, ensuring that we always have the most up-to-date value.

信息

FutureProvider does not offer a way of directly modifying the computation after a user interaction. It is designed to solve simple use-cases.
For more advanced scenarios, consider using AsyncNotifierProvider.

Usage example: reading a configuration file

FutureProvider can be a convenient way to expose a Configuration object created by reading a JSON file.

Creating the configuration would be done with your typical async/await syntax, but inside the provider. Using Flutter's asset system, this would be:

@riverpod
Future<Configuration> fetchConfiguration(Ref ref) async {
  final content = json.decode(
    await rootBundle.loadString('assets/configurations.json'),
  ) as Map<String, Object?>;

  return Configuration.fromJson(content);
}

Then, the UI can listen to configurations like so:

Widget build(BuildContext context, WidgetRef ref) {
  final config = ref.watch(fetchConfigurationProvider);

  return switch (config) {
    AsyncError(:final error) => Text('Error: $error'),
    AsyncData(:final value) => Text(value.host),
    _ => const CircularProgressIndicator(),
  };
}

This will automatically rebuild the UI when the Future completes. At the same time, if multiple widgets want the configurations, the asset will be decoded only once.

As you can see, listening to a FutureProvider inside a widget returns an AsyncValue – which allows handling the error/loading states.

Usage example: reading a configuration file​

Usage example: reading a configuration file