I suppose, it is some basic stuff.
I’ve tried to create a localized app according to this manual and the following instructions. Everething worked until I’ve tried to implement a field with a hint message.
The form which I’ve tried to implement (form.dart):
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:flutter/widgets.dart';
import 'package:flutter/services.dart';
import 'package:flutter_gen/gen_l10n/app_localizations.dart';
class MyCustomForm extends StatelessWidget {
const MyCustomForm({super.key});
@override
Widget build(BuildContext context) {
final local_delegate = AppLocalizations.of(context);
return Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
const Padding(
padding: EdgeInsets.symmetric(horizontal: 8, vertical: 16),
child: TextField(
decoration: InputDecoration(
border: OutlineInputBorder(),
hintText: local_delegate?.search_term, // a line with an error
),
),
),
Padding(
padding: const EdgeInsets.symmetric(horizontal: 8, vertical: 16),
child: new TextFormField(
keyboardType: TextInputType.number,
inputFormatters: [FilteringTextInputFormatter(new RegExp(r'[+-]?([0-9]*[.])?[0-9]+'), allow: true)],
decoration: const InputDecoration(
filled: true,
fillColor: CupertinoColors.white,
border: const OutlineInputBorder(),
labelText: 'Amount invested',
prefixText: '\R',
suffixText: 'ZAR',
suffixStyle:
const TextStyle(color: Colors.green)),
maxLines: 1,
validator: (String? value) {
if (value != null && value.isEmpty) {
return "Amount is required";
}
return null;
},
),
),
],
);
}
}
I’ve tried to use both operators Null assertion (!) and Conditional member access (?.) operators, this results in “Invalid constant value” error. Also I tried to do thing like that String(local_delegate?.search_term), but recieved error like this “The class ‘String’ doesn’t have an unnamed constant constructor. Try calling a different constructor.”
I’ve also tried to use these solutions:
Flutter i18n shortcut
Flutter: SearchBar hint text with internationalization.
Another solution suggests to remove const from the decoration line decoration: const InputDecoration
But still the code doesn’t compile.
What is the right way to use the i18n in that case?
The app:
import 'package:flutter/material.dart';
import 'package:flutter_gen/gen_l10n/app_localizations.dart';
import 'package:flutter_localizations/flutter_localizations.dart';
import 'form.dart';
class MyApp extends StatelessWidget {
const MyApp({super.key});
// This widget is the root of your application.
@override
Widget build(BuildContext context) {
return MaterialApp(
onGenerateTitle: (context) => AppLocalizations.of(context)!.title,
theme: ThemeData(
// This is the theme of your application.
//
// TRY THIS: Try running your application with "flutter run". You'll see
// the application has a blue toolbar. Then, without quitting the app,
// try changing the seedColor in the colorScheme below to Colors.green
// and then invoke "hot reload" (save your changes or press the "hot
// reload" button in a Flutter-supported IDE, or press "r" if you used
// the command line to start the app).
//
// Notice that the counter didn't reset back to zero; the application
// state is not lost during the reload. To reset the state, use hot
// restart instead.
//
// This works for code too, not just values: Most code changes can be
// tested with just a hot reload.
colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
useMaterial3: true,
),
localizationsDelegates: [
AppLocalizations.delegate,
GlobalMaterialLocalizations.delegate,
GlobalWidgetsLocalizations.delegate,
GlobalCupertinoLocalizations.delegate,
],
supportedLocales: [
Locale('en'), // English
],
home: const MyHomePage(),
);
}
}
class MyHomePage extends StatefulWidget {
const MyHomePage({super.key});
// This widget is the home page of your application. It is stateful, meaning
// that it has a State object (defined below) that contains fields that affect
// how it looks.
// This class is the configuration for the state. It holds the values (in this
// case the title) provided by the parent (in this case the App widget) and
// used by the build method of the State. Fields in a Widget subclass are
// always marked "final".
@override
State<MyHomePage> createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
int _counter = 0;
void _incrementCounter() {
setState(() {
// This call to setState tells the Flutter framework that something has
// changed in this State, which causes it to rerun the build method below
// so that the display can reflect the updated values. If we changed
// _counter without calling setState(), then the build method would not be
// called again, and so nothing would appear to happen.
_counter++;
});}
void _decrementCounter() {
setState(() {
// This call to setState tells the Flutter framework that something has
// changed in this State, which causes it to rerun the build method below
// so that the display can reflect the updated values. If we changed
// _counter without calling setState(), then the build method would not be
// called again, and so nothing would appear to happen.
_counter--;
});
}
@override
Widget build(BuildContext context) {
final local_delegate = AppLocalizations.of(context);
// This method is rerun every time setState is called, for instance as done
// by the _incrementCounter method above.
//
// The Flutter framework has been optimized to make rerunning build methods
// fast, so that you can just rebuild anything that needs updating rather
// than having to individually change instances of widgets.
return Scaffold(
appBar: AppBar(
// TRY THIS: Try changing the color here to a specific color (to
// Colors.amber, perhaps?) and trigger a hot reload to see the AppBar
// change color while the other colors stay the same.
backgroundColor: Theme.of(context).colorScheme.inversePrimary,
// Here we take the value from the MyHomePage object that was created by
// the App.build method, and use it to set our appbar title.
title: Text(AppLocalizations.of(context)!.title),
),
body: Center(
// Center is a layout widget. It takes a single child and positions it
// in the middle of the parent.
child: Column(
// Column is also a layout widget. It takes a list of children and
// arranges them vertically. By default, it sizes itself to fit its
// children horizontally, and tries to be as tall as its parent.
//
// Column has various properties to control how it sizes itself and
// how it positions its children. Here we use mainAxisAlignment to
// center the children vertically; the main axis here is the vertical
// axis because Columns are vertical (the cross axis would be
// horizontal).
//
// TRY THIS: Invoke "debug painting" (choose the "Toggle Debug Paint"
// action in the IDE, or press "p" in the console), to see the
// wireframe for each widget.
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text(
// 'You have pushed the button this many times:',
local_delegate!.push_text,
),
Text(
'$_counter',
style: Theme.of(context).textTheme.headlineMedium,
),
MyCustomForm()],
),
),
floatingActionButton: Column(
mainAxisAlignment: MainAxisAlignment.end,
children: [
FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'Increment',
child: const Icon(Icons.add)),
FloatingActionButton(
onPressed: _decrementCounter,
tooltip: 'Decrement',
child: const Icon(Icons.remove),
),
]
),
// This trailing comma makes auto-formatting nicer for build methods.
);
}
}
The main.dart
import 'src/app.dart';
import 'package:flutter/material.dart';
void main() {
runApp(const MyApp());
}
The localisation app_en.arb
{
"title": "Test title",
"push_text": "You have pushed the button this many times:",
"search_term": "Enter a search term",
"@search_term": {
"description": "Enter a search term"
}
}