ChangeNotifierProxyProvider getting null value - flutter

Question

I am new to flutter.
In my application locale information is found when the user login.
So the idea is when the user login, it will pass the locale to AppLanguage.
I have written ChangeNotifierProxyProvider to get the locale inside authentication information and create a AppLanuage object
In the ChangeNotifierProxyProvider I am getting appLang as null. auth object is correctly NOT null.
What I don't understand why I am getting null?
I did create it here right?
create: (_) => AppLanguage(),
shouldn't it come as a parameter for the update?
Widget build(BuildContext context) {
return MultiProvider(
providers: [
ChangeNotifierProvider.value(value: Auth()),
ChangeNotifierProxyProvider<Auth, AppLanguage>(
create: (_) => AppLanguage(),
update: (ctx, auth, appLang) {
print(auth);
print(appLang);
}
//appLang.setLocale(auth == null ? 'en' : auth.language),
),
],
child: Consumer2<Auth, AppLanguage>(
builder: (ctx, auth, lang, child) => MaterialApp(
title: 'Test App',
theme: ThemeData(
primarySwatch: Colors.blue,
visualDensity: VisualDensity.adaptivePlatformDensity,
),
locale: lang.appLocal,
supportedLocales: [
const Locale('en', 'US'),
const Locale('ja', ''),
],
localizationsDelegates: [
AppLocalizations.delegate,
GlobalMaterialLocalizations.delegate,
GlobalWidgetsLocalizations.delegate,
],
home: LandingView(),
),
),
);
}

Answer 1

I would try something like:
ChangeNotifierProxyProvider<Auth, AppLanguage>(
create: (_) => AppLanguage(),
update: (ctx, auth, appLang) => appLang..update(auth),
),
class AppLanguage with ChangeNotifier {
void update(Auth auth) {
// Do some custom work based on myModel that may call `notifyListeners`
}
}
That way your child will be able to get the correct updated values when they're available.
You can check more how to deal properly with that on the provider docs.