在TextFormField中插入破折号

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('Insert Dash in TextFormField'),
        ),
        body: Center(
          child: Padding(
            padding: EdgeInsets.all(20.0),
            child: TextFormField(
              inputFormatters: [
                WhitelistingTextInputFormatter.digitsOnly,
                LengthLimitingTextInputFormatter(12),
                _DashFormatter(),
              ],
              keyboardType: TextInputType.number,
              decoration: InputDecoration(
                labelText: 'Phone Number',
              ),
            ),
          ),
        ),
      ),
    );
  }
}

class _DashFormatter extends TextInputFormatter {
  @override
  TextEditingValue formatEditUpdate(
      TextEditingValue oldValue, TextEditingValue newValue) {
    String formattedText = newValue.text.replaceAll(RegExp(r'(\d{3})(\d{3})(\d{4})'), r'$1-$2-$3');
    return newValue.copyWith(text: formattedText);
  }
}