Impara Riverpod Fundamentals | State Management

Riverpod is a modern state management library for Flutter that stands out for its robust compile-time safety and flexibility. Unlike older solutions, Riverpod ensures that errors related to state management are caught during development, not at runtime. This leads to more reliable, maintainable code and a smoother debugging experience. By making dependencies explicit and supporting advanced features like hot-reload, Riverpod helps you build scalable Flutter apps with confidence.

main.dart


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import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';

// Define a StateProvider for an integer counter.
final counterProvider = StateProvider<int>((ref) => 0);

void main() {
  runApp(
    ProviderScope(
      child: MyApp(),
    ),
  );
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: CounterScreen(),
    );
  }
}

class CounterScreen extends ConsumerWidget {
  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final count = ref.watch(counterProvider);
    return Scaffold(
      appBar: AppBar(title: Text('Riverpod Counter')),
      body: Center(
        child: Text('Count: $count', style: TextStyle(fontSize: 32)),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () => ref.read(counterProvider.notifier).state++,
        child: Icon(Icons.add),
      ),
    );
  }
}

In Riverpod, a provider is a way to declare a piece of state or logic that can be shared and accessed throughout your app. The counterProvider in the example above is a StateProvider, which holds a simple integer value. A consumer is any widget or function that reads and reacts to changes in a provider's value. In the CounterScreen widget, you use ref.watch(counterProvider) to listen to the counter's value, and ref.read(counterProvider.notifier).state++ to update it. This separation of state declaration and consumption makes your code more modular and testable.

main.dart


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import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';

// Define a FutureProvider that fetches a string asynchronously.
final helloProvider = FutureProvider<String>((ref) async {
  await Future.delayed(Duration(seconds: 2));
  return 'Hello from Riverpod!';
});

void main() {
  runApp(
    ProviderScope(
      child: MyApp(),
    ),
  );
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: AsyncHelloScreen(),
    );
  }
}

class AsyncHelloScreen extends ConsumerWidget {
  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final asyncValue = ref.watch(helloProvider);

    return Scaffold(
      appBar: AppBar(title: Text('FutureProvider Example')),
      body: Center(
        child: asyncValue.when(
          data: (value) => Text(value, style: TextStyle(fontSize: 24)),
          loading: () => CircularProgressIndicator(),
          error: (err, stack) => Text('Error: $err'),
        ),
      ),
    );
  }
}

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Sezione 1. Capitolo 3

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main.dart


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import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';

// Define a StateProvider for an integer counter.
final counterProvider = StateProvider<int>((ref) => 0);

void main() {
  runApp(
    ProviderScope(
      child: MyApp(),
    ),
  );
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: CounterScreen(),
    );
  }
}

class CounterScreen extends ConsumerWidget {
  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final count = ref.watch(counterProvider);
    return Scaffold(
      appBar: AppBar(title: Text('Riverpod Counter')),
      body: Center(
        child: Text('Count: $count', style: TextStyle(fontSize: 32)),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () => ref.read(counterProvider.notifier).state++,
        child: Icon(Icons.add),
      ),
    );
  }
}

main.dart


              12345678910111213141516171819202122232425262728293031323334353637383940414243
            
import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';

// Define a FutureProvider that fetches a string asynchronously.
final helloProvider = FutureProvider<String>((ref) async {
  await Future.delayed(Duration(seconds: 2));
  return 'Hello from Riverpod!';
});

void main() {
  runApp(
    ProviderScope(
      child: MyApp(),
    ),
  );
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: AsyncHelloScreen(),
    );
  }
}

class AsyncHelloScreen extends ConsumerWidget {
  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final asyncValue = ref.watch(helloProvider);

    return Scaffold(
      appBar: AppBar(title: Text('FutureProvider Example')),
      body: Center(
        child: asyncValue.when(
          data: (value) => Text(value, style: TextStyle(fontSize: 24)),
          loading: () => CircularProgressIndicator(),
          error: (err, stack) => Text('Error: $err'),
        ),
      ),
    );
  }
}

Tutto è chiaro?

Grazie per i tuoi commenti!

Sezione 1. Capitolo 3