Cannot replace a string in Dart - flutter

Question

I'm re-writing a simple application to calculate averages, however I have a hard time with a TextField.
I set the TextField to be able to replace a comma to a period if a locale is en_US, otherwise it should replace a period to a comma if locale is different than en_US. However, replaceAll() method doesn't seem to work.
Sorry for the code quality, but I will fix it after I see where's the problem.
Code:
import 'package:flutter/material.dart';
import 'package:easy_localization/easy_localization.dart';
import 'package:flutter/services.dart';
class ArithmeticAverageScreen extends StatefulWidget {
#override
_ArithmeticAverageScreenState createState() => _ArithmeticAverageScreenState();
}
class _ArithmeticAverageScreenState extends State<ArithmeticAverageScreen> {
var _grades = List<Widget>();
var _textFieldController = TextEditingController();
var _gradesList = List<String>();
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('arithmetic_average_title').tr(),
),
body: Container(
padding: EdgeInsets.all(16.0),
child: ListView(
children: <Widget>[
Card(
child: Container(
padding: EdgeInsets.symmetric(vertical: 20.0),
child: Column(
mainAxisSize: MainAxisSize.min,
children: <Widget>[
ListTile(
leading: Icon(Icons.help),
title: Text('arithmetic_average_help').tr(),
subtitle: Text('arithmetic_average_help_content').tr(),
)
],
),
)
),
SizedBox(height: 16.0),
Card(
child: Container(
padding: EdgeInsets.symmetric(vertical: 20.0, horizontal: 20.0),
child: Column(
mainAxisSize: MainAxisSize.min,
crossAxisAlignment: CrossAxisAlignment.stretch,
children: <Widget>[
Text('arithmetic_average_your_grades', style: Theme.of(context).textTheme.headline5).tr(),
SizedBox(height: 16.0),
Text('arithmetic_average_grades_one_at_a_time', style: Theme.of(context).textTheme.headline6,).tr(),
SizedBox(height: 16.0),
Row(
children: <Widget>[
Container(
width: 60.0,
child: TextField(
controller: _textFieldController,
inputFormatters: [ WhitelistingTextInputFormatter(RegExp("[0-9,.]")) ],
decoration: InputDecoration(
hintText: '5',
labelText: 'arithmetic_average_grade'.tr()
),
),
),
SizedBox(width: 20.0,),
RaisedButton(
onPressed: () {
if (_textFieldController.text == '') {
showDialog(
context: context,
builder: (context) {
return AlertDialog(
content: Text('arithmetic_average_type_number').tr(),
);
}
);
}
else {
String locale = Localizations.localeOf(context).toString();
if (locale == 'en_US') {
if (_textFieldController.text.contains(',')) {
print('True');
_textFieldController.text.replaceAll(',', '.');
}
}
else if (locale == 'pl_PL') {
if (_textFieldController.text.contains('.')) {
_textFieldController.text.replaceAll('.', ',');
}
}
setState(() {
_gradesList.add(_textFieldController.text);
print(_gradesList);
_grades.add(Text(_textFieldController.text));
});
}
},
color: Colors.teal[300],
textColor: Colors.white,
child: Text('arithmetic_average_add_button').tr(),
),
],
),
SizedBox(height: 16.0,),
Wrap(
children: _grades,
),
],
),
),
)
],
),
)
);
}
}

Answer 1

In the following line, you are not updating the text of the text field so replace the following
_textFieldController.text.replaceAll(',', '.');
with this
_textFieldController.text = _textFieldController.text.replaceAll(',', '.')