Using GlobalMaterialLocalizations.delegate provides error

Question

EDIT: Answer was very simple:

await initializeDateFormatting('pl_PL');

Above code was in conflict with:

GlobalMaterialLocalizations.delegate

Removing initializeDateFormatting helps.

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I made a localization on my Flutter app. Unfortunately when I add GlobalMaterialLocalizations.delegate to localizationsDelegates there is an error. Removing GlobalMaterialLocalizations.delegate provides app to work correctly but only English version. Another language (Polish) has a problem with AppBars (Again - after removing it (appbar) app works fine in that language too).

Part of my code:

localizationsDelegates: [
  const ReadyLocalizationsDelegate(),
  GlobalMaterialLocalizations.delegate,
  GlobalWidgetsLocalizations.delegate,
],
supportedLocales: [
  const Locale('en', 'US'),
  const Locale('pl', 'PL'),
],

Error:

Unsupported operation: Cannot set value in unmodifiable Map

Here is an error when I comment GlobalMaterialLocalizations.delegate (page has AppBar): https://pastebin.com/ENF5ZET7

As I said there is no error when localization is set to English.

Answer 1

If you just want to use the system's locale setting, there is no need to call initializeDateFormatting(). In your main.dart before calling runApp(), do this:

await findSystemLocale();

To call this method, you will need this import:

import 'package:intl/intl_standalone.dart';

As a reference, there is some documentation here -- https://api.flutter.dev/flutter/intl/Intl/systemLocale.html

Answer 2

await initializeDateFormatting('pl_PL');

Above code was in conflict with:

GlobalMaterialLocalizations.delegate

Removing initializeDateFormatting helps.