How to pass data down the widget tree?

Question

I have read and understood a similar question posted here, but am having trouble applying it to my use case. I am new to Flutter and am creating an app that streams audio from a given URL using Ryan Heise's audio_service plugin. Using this plugin I instantiate an audioHandler immediately upon starting my app:

late AudioHandler audioHandler;

Future<void> main() async {
  WidgetsFlutterBinding.ensureInitialized();
  final session = await AudioSession.instance;
  await session.configure(const AudioSessionConfiguration.music());
  audioHandler = await AudioService.init(
    builder: () => AudioPlayerHandler(),
    config: const AudioServiceConfig(
      androidNotificationChannelId: 'com.ryanheise.myapp.channel.audio',
      androidNotificationChannelName: 'Channel Name',
      androidNotificationOngoing: true,
    ),
  );
  runApp(const MyApp());
}

With this audioHandler initialized, I would like to use it in child widgets. The example below demonstrates one such child widget:

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

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
        debugShowCheckedModeBanner: false,
        title: "Koradi Radio",
        theme: ThemeData(
          brightness: Brightness.light,
          scaffoldBackgroundColor: Colors.white70,
        ),
        darkTheme: ThemeData(
          brightness: Brightness.dark,
        ),
        themeMode: ThemeMode.system,
        home: const EnglishHome());
  }
}

class EnglishHome extends StatefulWidget {
  const EnglishHome({Key? key}) : super(key: key);

  @override
  _EnglishHomeState createState() => _EnglishHomeState();
}


class _EnglishHomeState extends State<EnglishHome> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('English Radio'),
        backgroundColor: Colors.transparent,
      ),
      body: ... 
    }
}

Note that MyApp currently just routes to EnglishHome(), but I plan on adding additional languages and instead routing MyApp to a page where a user can select their language. How can I pass audioHandler to all descendent widgets from Main() ? (EnglishHome, EspHome, FrenchHome, etc?) Based upon what I have read, I will either be modifying the Key parameter of child widgets or else their BuildContext?

score 2 · Accepted Answer · answered Jan 16 '22 at 02:19

You can use provider package and all you need to do is use Provider.value and then use Provider.of(context) in your EnglishHome, FrenchHome etc classes.

late AudioHandler audioHandler;

Future<void> main() async {
  audioHandler = await AudioService.init(...);
  runApp(MyApp(audioHandler));
}

class MyApp extends StatelessWidget {
  final AudioHandler audioHandler;
  const MyApp(this.audioHandler, {Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Provider.value(
      value: audioHandler, // Providing the data above MaterialApp
      child: MaterialApp(
        home: EnglishHome(),
      ),
    );
  }
}

class EnglishHome extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    // Accessing the data. 
    final audioHandler = Provider.of<AudioHandler>(context);
    return Container();
  }
}

score 0 · Answer 2 · answered Jan 16 '22 at 16:40

The other answers here are also valid solutions, but what I was able to do was add an audioHandler parameter to EnglishHome:

class EnglishHome extends StatefulWidget {
  var audioHandler;

  EnglishHome({Key? key, this.audioHandler}) : super(key: key);

  @override
  _EnglishHomeState createState() => _EnglishHomeState();

And then pass the audioHandler in when the Widget was called from my main.dart file:

@override
  Widget build(BuildContext context) {
    return MaterialApp(
        debugShowCheckedModeBanner: false,
        title: "Radio",
        theme: ThemeData(
          brightness: Brightness.light,
          scaffoldBackgroundColor: Colors.blue[100],
        ),
        darkTheme: ThemeData(
          brightness: Brightness.dark,
        ),
        themeMode: ThemeMode.system,
        home: EnglishHome(
          audioHandler: audioHandler,
        ));
  }
}

How to pass data down the widget tree?

2 Answers2