UnsupportedError thrown when setting localizationsDelegates - flutter

Question

I'm trying to implement internationalization for my Flutter app but it won't let me use my preferred language (Indonesian).
From the docs, it told me to add localizationsDelegates to my MaterialApp. Since I am using GetX, the MaterialApp here are wrapped inside the GetMaterialApp.
But when I did that, it throws me an error:
Exception has occurred.
UnsupportedError (Unsupported operation: Cannot modify unmodifiable map)
I tried to remove the localizationsDelegates, it throws me yet another error:
Exception has occurred.
FlutterError (No MaterialLocalizations found.
TabBar widgets require MaterialLocalizations to be provided by a Localizations widget ancestor.
The material library uses Localizations to generate messages, labels, and abbreviations.
To introduce a MaterialLocalizations, either use a MaterialApp at the root of your application to include them automatically, or add a Localization widget with a MaterialLocalizations delegate.
The specific widget that could not find a MaterialLocalizations ancestor was:
TabBar
But when I hard code the locale property of my GetMaterialApp to Locale('en', 'US') and commented the localizationsDelegates, it works.
Do you guys know why and how to fix this?
Anyways, here is how my main.dart (and some related files) look like.
main.dart
void main() async {
WidgetsFlutterBinding.ensureInitialized();
await Get.putAsync(() => EnvService().init());
await Get.putAsync(() => IntlService().init());
runApp(const MyApp());
}
class MyApp extends StatelessWidget {
const MyApp({super.key});
#override
Widget build(BuildContext context) {
return GetMaterialApp(
title: "MyApp",
initialRoute: AppPages.INITIAL,
getPages: AppPages.routes,
themeMode: ThemeMode.dark,
theme: MyAppTheme.light,
darkTheme: MyAppTheme.dark,
debugShowCheckedModeBanner: false,
// translations: AppTranslations(),
locale: const Locale('en', 'US'),
fallbackLocale: const Locale('id', 'ID'),
supportedLocales: const [
Locale('en', 'US'),
Locale('id', 'ID'),
],
//
//
// UNCOMMENT THIS LINE, YOUR PHONE WILL EXPLODE!
// localizationsDelegates: GlobalMaterialLocalizations.delegates,
);
}
}
env_service.dart
class EnvService extends GetxService {
static EnvService get instance => Get.find();
Future<EnvService> init() async {
await dotenv.load();
return this;
}
Locale get defaultLocale {
final locale = dotenv.get('DEFAULT_LOCALE', fallback: 'id');
if (locale != 'id') {
return const Locale('en', 'US');
}
return Locale(locale, locale.toUpperCase());
}
}
intl_service.dart
class IntlService extends GetxService {
static IntlService get instance => Get.find();
Locale get _locale {
return Get.locale ?? EnvService.instance.defaultLocale;
}
Future<IntlService> init() async {
await initializeDateFormatting(_locale.countryCode);
return this;
}
String formatCurrency(double number) {
final formatter = NumberFormat.simpleCurrency(decimalDigits: 0);
return formatter.format(number);
}
String formatDate(DateTime? dateTime, [String? format]) {
if (dateTime == null) {
return '';
}
return DateFormat(format).format(dateTime);
}
}

Answer 1

try add this in GetMaterialApp:
localizationsDelegates: [
GlobalMaterialLocalizations.delegate,
GlobalWidgetsLocalizations.delegate,
GlobalCupertinoLocalizations.delegate,
],

Answer 2

It should work if you remove initializeDateFormatting(). And be aware that Hot Reload might not work if you make this change.
This works because initializeDateFormatting() calls initializeDatePatterns() with a const Map setting dateTimePatterns which is immutable after that. But GlobalMaterialLocalizations.delegate calls initializeDateFormattingCustom() which tries to write its map into dateTimePatterns at the end. That results in an "Unsupported operation: Cannot modify unmodifiable map". So if we do not call initializeDateFormatting(), this error does not happen because dateTimePatterns is not immutable when initializeDateFormattingCustom() is called. But the date formatting is initialized anyway because that is what initializeDateFormattingCustom() does with the formatting from GlobalMaterialLocalizations.
This depends on intl ^0.17.0.