I'm adding localization support to a webpage I'm building using Flutter dart. I can see that the title is displayed correctly using S.current.name property, but when the build comes to the widgets, it fails with the following error:

Assertion failed: file:///C:/dev/Adri/lib/generated/l10n.dart:21:12
_current != null
"No instance of S was loaded. Try to initialize the S delegate before accessing S.current."

My main() and HomePage looks like this:

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

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

  @override
  Widget build(BuildContext context) {
    return ChangeNotifierProvider<LanguageChangeProvider>(
      create: (context) => LanguageChangeProvider(),
      child: Builder(
        builder: (context) => MaterialApp(
            debugShowCheckedModeBanner: false,
            locale: Provider.of<LanguageChangeProvider>(context, listen: true)
                .currentLocale,
            localizationsDelegates: const [
              S.delegate,
              GlobalMaterialLocalizations.delegate,
              GlobalWidgetsLocalizations.delegate,
              GlobalCupertinoLocalizations.delegate
            ],
            supportedLocales: S.delegate.supportedLocales,
            //title: S.current.name,
            home: MyHomePage(title: S.current.name,)),
      ),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key, required this.title});
  
  final String title;

  @override
  State<StatefulWidget> createState() => _MyHomePageState();
}

As you can see, the S.current.name can be successfully passed down as the title of the website:

But it seems that the rest of the HomeScreen is unable to access this S for some reason:

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          actions: [
            IconButton(
                tooltip: SELECT_LANG_HU,
                onPressed: () {
                  languageChangeProcess(context, LOCALE_HU);
                },
                icon: const Icon(Icons.language)),
            IconButton(
                tooltip: SELECT_LANG_EN,
                onPressed: () {
                  languageChangeProcess(context, LOCALE_EN);
                },
                icon: const Icon(Icons.change_circle))
          ],
          iconTheme: const IconThemeData(color: Colors.grey),
          title: Text(
            S.current.name,
            style: TextStyle(color: Colors.grey.shade600),
          ),
          flexibleSpace: Container(
            decoration: BoxDecoration(
                gradient: LinearGradient(colors: <Color>[
              Colors.teal.shade50,
              Colors.teal.shade100,
            ])),
          ),
        ),
        body: Row(
          children: [Expanded(flex: 1, child: Container())],
        ),
        drawer: Drawer(
          child: ListView(
            children: [
              DrawerHeader(
                  decoration: BoxDecoration(
                      gradient: LinearGradient(colors: <Color>[
                    Colors.teal.shade50,
                    Colors.teal.shade100
                  ])),
                  padding:
                      const EdgeInsets.only(left: 2.0, right: 2.0, top: 4.0),
                  child: const ContactCard()),
              MenuElement(Icons.person, S.current.introduction, () => {}),
              MenuElement(Icons.school, S.current.education, () => {}),
              MenuElement(
                  Icons.workspace_premium, S.current.publications, () => {}),
              MenuElement(Icons.work, S.current.workExperience, () => {}),
            ],
          ),
        ));
  }

Am I missing something obvious?

In the pubsec.yaml I added this dependency:

  flutter_localizations:
    sdk: flutter
  provider: ^5.0.0

CodePudding user response：

• Did you add the code below to pubspec.yaml?

flutter:
  generate: true

If you haven't added it, you can check it out here. fluttter.dev

CodePudding user response：

By the way, you have to call your string from the localization file like this: For example: S.of(context)!.title

Recommendation: Instead of calling

localizationsDelegates: const [
              S.delegate,
              GlobalMaterialLocalizations.delegate,
              GlobalWidgetsLocalizations.delegate,
              GlobalCupertinoLocalizations.delegate
            ],

You can call this one :

 localizationsDelegates: S.localizationsDelegates,

This is the short version of calling localizationsDelegates

CodePudding user response：

I seem to have found a solution for my problem, if I initialize the localization inside main(), it will work (except for the title, but that's the least of issues).

void main() {
  runApp(ChangeNotifierProvider<LanguageChangeProvider>(
    create: (context) => LanguageChangeProvider(),
    child: Builder(
        builder: (context) => MaterialApp(
              localizationsDelegates: const [
                S.delegate,
                GlobalMaterialLocalizations.delegate,
                GlobalWidgetsLocalizations.delegate,
                GlobalCupertinoLocalizations.delegate
              ],
              debugShowCheckedModeBanner: false,
              locale: Provider.of<LanguageChangeProvider>(context, listen: true)
                  .currentLocale,
              supportedLocales: S.delegate.supportedLocales,
              home: HomeScreen(),
            )),
  ));
}

class HomeScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MyHomePage();
  }
}

Swapping between localizations works now like a charm.