Flutter Riverpod Tutorial Part 2: Asynchronous Providers (FutureProvider and StreamProvider)

Part-1 Link : https://harishkunchala.com/flutter-riverpod-tutorial-part-1-provider-and-stateprovider-statenotifierprovider-changenotifierprovider

FutureProvider

1. FutureProvider allows us to work with Futures in our Flutter Application

2. It automatically handles the lifecycle of asynchronous operation.

3. So it provides us with a way to react to the different states of the future: loading, error and data.

Step 1: Add http to our pubspec.yaml

We are going to look at an actual networking example by showing either a single user or list of users from JsonPlaceHolder Users API. So let's add http into our pubspec.yaml

flutter pub add http

Step 2: Create a FutureProvider for Fetching Data

First, we need to set up the FutureProvider. We will create a function that fetches data from the JSON Placeholder Users API and returns a list of users:

import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:http/http.dart' as http;
import 'dart:convert'; // Required for jsonDecode

final usersProvider = FutureProvider<List<dynamic>>((ref) async {
  final url = Uri.parse('https://jsonplaceholder.typicode.com/users');
  final response = await http.get(url);

  if (response.statusCode == 200) {
    return jsonDecode(response.body);
  } else {
    throw Exception('Failed to load users');
  }
});

Step 3: Building the UI to Display Data

Now, let's create the UI part where we use usersProvider to display the list of users or handle loading and error states:

class UsersScreen extends ConsumerWidget {
  const UsersScreen({super.key});

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final usersAsyncValue = ref.watch(usersProvider);
    return Scaffold(
      appBar: AppBar(
        title: const Text('Users'),
      ),
      body: usersAsyncValue.when(
        loading: () => const Center(child: CircularProgressIndicator()),
        error: (error, stackTrace) => Center(child: Text('Error: $error')),
        data: (users) => ListView.builder(
          itemCount: users.length,
          itemBuilder: (context, index) {
            return ListTile(
              title: Text(users[index]['name']),
              subtitle: Text(users[index]['email']),
            );
          },
        )
      ),
    );
  }

If we look closely in the above example:

usersAsyncValue.when() handles the three states:

• loading: Displays a circular progress indicator.

• error: Shows an error message.

• data: Builds a list of users using a ListView.builder.

Step 4: Run Our App

This is our current output:

As always you can find the source code here: https://github.com/khkred/flutter_stack/tree/future_provider

StreamProvider

Step 1: Create a StreamProvider

First, define a StreamProvider that sets up a stream. We'll use Dart's Stream.periodic to create a simple stream that emits an incrementing integer every second:

final counterStreamProvider = StreamProvider<int>((ref) {
  return Stream.periodic(const Duration(seconds: 1), (count) =>  count +1);
});

This provider creates a stream that emits an incrementing count every second, starting from 1.

Step 2: Building the UI to Display our Stream Data

We will use a ConsumerWidget to consume the counterStreamProvider and update the UI every time a new value is emitted by the stream:

class CounterStreamScreen extends ConsumerWidget {
  const CounterStreamScreen({super.key});

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final counterAsyncValue = ref.watch(counterStreamProvider);
    return Scaffold(
      appBar: AppBar(
        title: const Text('Counter Stream'),
      ),
      body: Center(
        child: counterAsyncValue.when(
          data: (count) => Text('Current Count: $count', style: const TextStyle(fontSize: 24)),
          loading: () => const CircularProgressIndicator(),
          error: (error, stackTrace) => Text('Error: $error'),
        ),
      ),
    );
  }
}

In the above example:

• counterAsyncValue.when() handles the different states:

  • loading: Shows a circular progress indicator before the first value is emitted.

  • error: Displays an error message if there's an issue with the stream.

  • data: Updates the displayed count each time a new value is emitted from the stream.

Step 3: Run our App

Here's our Counter Stream Screen:

And as always you can find the source code here: https://github.com/khkred/flutter_stack/tree/stream_provider

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