Flutter Form Validator

import 'package:flutter/material.dart';

void main() => runApp(const MyApp());

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: const HomePage(),
      theme: ThemeData(
        brightness: Brightness.dark,
      ),
    );
  }
}

class HomePage extends StatefulWidget {
  const HomePage({super.key});

  @override
  State createState() => _HomePageState();
}

class _HomePageState extends State {
  final _formKey = GlobalKey();
  var isLoading = false;

  void _submit() {
    final isValid = _formKey.currentState!.validate();
    if (!isValid) {
      return;
    }
    _formKey.currentState!.save();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text("Nextgen Tutorial"),
        centerTitle: true,
      ),
      //body
      body: Padding(
        padding: const EdgeInsets.all(16.0),
        //form
        child: Form(
          key: _formKey,
          child: Column(
            children: [
              const Text(
                "Validasi Form di Flutter ",
                style: TextStyle(fontSize: 24.0, fontWeight: FontWeight.bold),
              ),
              //styling
              SizedBox(
                height: MediaQuery.of(context).size.width * 0.1,
              ),
              TextFormField(
                decoration: const InputDecoration(labelText: 'Email'),
                keyboardType: TextInputType.emailAddress,
                onFieldSubmitted: (value) {
                  //Validator
                },
                validator: (value) {
                  if (value!.isEmpty ||
                      !RegExp(r"^[a-zA-Z0-9.a-zA-Z0-9.!#$%&'*+-/=?^_`{|}~]+@[a-zA-Z0-9]+\.[a-zA-Z]+")
                          .hasMatch(value)) {
                    return 'Masukkan email yang valid!';
                  }
                  return null;
                },
              ),
              //box styling
              SizedBox(
                height: MediaQuery.of(context).size.width * 0.1,
              ),
              //text input
              TextFormField(
                decoration: const InputDecoration(labelText: 'Password'),
                keyboardType: TextInputType.emailAddress,
                onFieldSubmitted: (value) {},
                obscureText: true,
                validator: (value) {
                  if (value!.isEmpty) {
                    return 'Masukkan Password yang valid!';
                  }
                  return null;
                },
              ),
              SizedBox(
                height: MediaQuery.of(context).size.width * 0.1,
              ),
              ElevatedButton(
                child: const Text(
                  "Submit",
                ),
                onPressed: () => _submit(),
              )
            ],
          ),
        ),
      ),
    );
  }
}