provider_example.dart

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

void main() {
  runApp(
    MultiProvider(
      providers: [
        // Counter is the name of the provider model
        // we will use to update the state of the Widgets
        ChangeNotifierProvider(create: (_) => Counter()),
      ],
      child: const MyApp(),
    ),
  );
}
class Counter with ChangeNotifier, DiagnosticableTreeMixin {
  int _count = 0;
  int get count => _count;

  void increment() {
    _count++;
    notifyListeners();
  }
}

class MyWidget extends StatelessWidget {
  const MyWidget({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Example'),
      ),
      body: Center(
        child: Column(
          children: const <Widget>[
            Text('You have pushed the button this many times:'),
            Count(),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        key: const Key('increment_floatingActionButton'),
        // access to the Counter provider using the context
        // and increments its value.
        onPressed: () => context.read<Counter>().increment(),
        tooltip: 'Increment',
        child: const Icon(Icons.add),
      ),
    );
  }
}

class Count extends StatelessWidget {
  const Count({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Text(
        // rebuilds the UI wach time the count variable is 
        // updated inside the provider using watch method
        '${context.watch<Counter>().count}',
        key: const Key('counterState'),
        style: Theme.of(context).textTheme.headline4);
  }
}