ChangeNotifier with provider

main.dart

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

/// Data model for the counter, extending ChangeNotifier to notify listeners of changes.
class CounterData extends ValueNotifier<int> {
  CounterData() : super(0);

  void increment() => value = value + 1;
}

/// A widget that displays the current count,
/// retrieved from the provided [CounterData] using Provider.
class CountDisplayWidget extends StatelessWidget {
  final int? counter;

  /// Creates a [CountDisplayWidget].
  const CountDisplayWidget({super.key, required this.counter});

  @override
  Widget build(context) {
    return Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: [
        const Text('Current Count:', style: TextStyle(fontSize: 20)),
        Text(
          counter?.toString() ?? '-',
          style: Theme.of(context).textTheme.headlineMedium,
        ),
      ],
    );
  }
}

/// The main application widget that builds the UI,
/// interacting with the counter state via Provider.
class HomePage extends StatelessWidget {
  const HomePage({super.key});

  @override
  Widget build(BuildContext context) {
    /// on recup la méthode increment du compteur
    final counterData = context.watch<CounterData?>();

    return Scaffold(
      appBar: AppBar(
        title: const Text('Counter Application'),
        backgroundColor: Theme.of(context).colorScheme.inversePrimary,
      ),
      body: Center(child: CountDisplayWidget(counter: counterData?.value)),
      floatingActionButton: FloatingActionButton(
        onPressed: counterData?.increment,
        tooltip: 'Increment',
        child: const Icon(Icons.add),
      ),
    );
  }
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Counter Application',
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
        useMaterial3: true,
      ),
      // Provide the CounterData ChangeNotifier to the widget tree.
      home: ChangeNotifierProvider(
        create: (context) => CounterData(),
        builder: (context, child) => const HomePage(),
      ),
    );
  }
}

void main() {
  runApp(const MyApp());
}