flutter regexp

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

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(title: Text('RegExp Example')),
        body: EmailValidator(),
      ),
    );
  }
}

class EmailValidator extends StatefulWidget {
  @override
  _EmailValidatorState createState() => _EmailValidatorState();
}

class _EmailValidatorState extends State<EmailValidator> {
  final _formKey = GlobalKey<FormState>();
  String _email = '';
  String _emailError = '';

  final emailRegExp = RegExp(
    r'^[a-zA-Z0-9.!#$%&'*+/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,253}[a-zA-Z0-9])?(?:\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,253}[a-zA-Z0-9])?)*$',
  );

  void _validateEmail() {
    if (_emailRegExp.hasMatch(_email)) {
      setState(() {
        _emailError = '';
      });
    } else {
      setState(() {
        _emailError = 'Invalid email address';
      });
    }
  }

  @override
  Widget build(BuildContext context) {
    return Form(
      key: _formKey,
      child: Column(
        children: [
          TextFormField(
            decoration: InputDecoration(labelText: 'Email'),
            onChanged: (value) {
              setState(() {
                _email = value;
              });
            },
          ),
          SizedBox(height: 10),
          Text(_emailError, style: TextStyle(color: Colors.red)),
          ElevatedButton(
            onPressed: _validateEmail,
            child: Text('Validate'),
          ),
        ],
      ),
    );
  }
}