provider 4.0.1

A mixture between dependency injection and state management, built with widgets for widgets.

example/lib/main.dart

// ignore_for_file: public_member_api_docs, lines_longer_than_80_chars
import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';

/// This is an example of a counter application using `provider` + [ChangeNotifier].
///
/// It builds a typical `+` button, with a twist: the texts using the counter
/// are built using the localization framework.
///
/// This shows how to bind our custom [ChangeNotifier] to things like [LocalizationsDelegate].

void main() => runApp(MyApp());

class Counter with ChangeNotifier {
  int _count = 0;
  int get count => _count;

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MultiProvider(
      providers: [
        ChangeNotifierProvider(create: (_) => Counter()),
      ],
      child: Consumer<Counter>(
        builder: (context, counter, _) {
          return MaterialApp(
            supportedLocales: const [Locale('en')],
            localizationsDelegates: [
              DefaultMaterialLocalizations.delegate,
              DefaultWidgetsLocalizations.delegate,
              _ExampleLocalizationsDelegate(counter.count),
            ],
            home: const MyHomePage(),
          );
        },
      ),
    );
  }
}

class ExampleLocalizations {
  static ExampleLocalizations of(BuildContext context) {
    return Localizations.of<ExampleLocalizations>(context, ExampleLocalizations);
  }

  const ExampleLocalizations(this._count);

  final int _count;

  String get title => 'Tapped $_count times';
}

class _ExampleLocalizationsDelegate extends LocalizationsDelegate<ExampleLocalizations> {
  const _ExampleLocalizationsDelegate(this.count);

  final int count;

  @override
  bool isSupported(Locale locale) => locale.languageCode == 'en';

  @override
  Future<ExampleLocalizations> load(Locale locale) {
    return SynchronousFuture(ExampleLocalizations(count));
  }

  @override
  bool shouldReload(_ExampleLocalizationsDelegate old) => old.count != count;
}

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      /// Tons of small widgets!
      ///
      /// Splitting our app in small widgets like [Title] or [CounterLabel] is
      /// useful for rebuild optimization.
      ///
      /// Since they are instanciated using `const`, they won't unnecessarily
      /// rebuild when their parent changes.
      /// But they can still have dynamic content, as they can obtain providers!
      ///
      /// This means only the widgets that depends on a provider to rebuild when they change.
      /// Alternatively, we could use [Consumer] or [Selector] to acheive the
      /// same result.
      appBar: AppBar(title: const Title()),
      body: const Center(child: CounterLabel()),
      floatingActionButton: const IncrementCounterButton(),
    );
  }
}

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

  @override
  Widget build(BuildContext context) {
    return FloatingActionButton(
      onPressed: () {
        Provider.of<Counter>(context, listen: false).increment();
      },
      tooltip: 'Increment',
      child: const Icon(Icons.add),
    );
  }
}

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

  @override
  Widget build(BuildContext context) {
    final counter = Provider.of<Counter>(context);
    return Column(
      mainAxisSize: MainAxisSize.min,
      mainAxisAlignment: MainAxisAlignment.center,
      children: <Widget>[
        const Text(
          'You have pushed the button this many times:',
        ),
        Text(
          '${counter.count}',
          style: Theme.of(context).textTheme.display1,
        ),
      ],
    );
  }
}

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

  @override
  Widget build(BuildContext context) {
    return Text(ExampleLocalizations.of(context).title);
  }
}