Best approach to null safe AppLocalization strings

Question

Question

I am using AppLocalizations.of(context).myString to internationalize strings in my null safe flutter app.

My IDE tells me that AppLocalizations.of(context) can return null. What's the best approach to handle this? Is there a way to ensure AppLocalizations.of(context) never returns null?

Currently, I am resorting to the following approach:

AppLocalizations.of(context)?.myString ?? 'Fallback string'

Full Project Code

Pubspec.yaml

name: Sample Intl Project
description: A sample project
publish_to: 'none'
version: 1.0.0+1
environment:
  sdk: ">=2.12.0-133.2.beta <3.0.0"
dependencies:
  flutter:
    sdk: flutter
  flutter_localizations:
    sdk: flutter
  intl: ^0.17.0-nullsafety.2
dev_dependencies:
  flutter_test:
    sdk: flutter
flutter:
  uses-material-design: true
  generate: true

l10n.yaml

arb-dir: lib/l10n
template-arb-file: app_en_US.arb
output-localization-file: app_localizations.dart

l10n/app_en_US.arb

{
  "helloWorld": "Hello World!",
  "@helloWorld": {
    "description": "Greeting"
}

l10n/app_en.arb

{
  "helloWorld": "Hello World!"
}

main.dart

import 'package:flutter/material.dart';
import 'package:flutter_gen/gen_l10n/app_localizations.dart';
void main() {
  runApp(App());
}
class App extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Sample App',
      localizationsDelegates: AppLocalizations.localizationsDelegates,
      supportedLocales: AppLocalizations.supportedLocales,
      home: Home()
    );
  }
}
class Home extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Center(
      child: Text(
        AppLocalizations.of(context)?.helloWorld ?? 'Hello World!'
      ),
    );
  }
}

Solution 1

If you are sure, that AppLocalizations.of(context) will always return a valid AppLocalizations instance (which is true for your sample application), you can use:

AppLocalizations.of(context)!.myString

The ! operator tells Dart, that AppLocalizations.of(context) will never return null and acts like a cast from the nullable AppLocalizations? to the non-nullable AppLocalizations.

Note: If AppLocalizations.of(context) returns null at runtime, then AppLocalizations.of(context)! will throw an exception.

Solution 2

add this line in l10n.yaml:

nullable-getter: false