import 'package:flutter/services.dart';
import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}
class MyHomePage extends StatefulWidget {
  MyHomePage({Key? key, required this.title}) : super(key: key);

  final String title;
  @override
  _MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(
          widget.title,
        ),
      ),
      body: Center(
        child: TextField(
          inputFormatters: [TestFormatter()],
          keyboardType: const TextInputType.numberWithOptions(decimal: true),
        ),
      ),
    );
  }
}
class TestFormatter extends TextInputFormatter {
  @override
  TextEditingValue formatEditUpdate(
      TextEditingValue oldValue,
      TextEditingValue newValue,
      ) {
    var formattedString = newValue.text;
    if (formattedString.length == 3) {
      formattedString = '${formattedString.substring(0, 1)},'
          '${formattedString.substring(1, formattedString.length)}';
    }
    return TextEditingValue(
      text: formattedString,
      selection: TextSelection.collapsed(offset: formattedString.length),
    );
  }
}