Flutter — готовые виджеты — Форма входа

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 LoginScreen());
  }
}

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

  @override
  State<LoginScreen> createState() => _LoginScreenState();
}

class _LoginScreenState extends State<LoginScreen> {
  final _formKey = GlobalKey<FormState>();
  final _loginController = TextEditingController();
  final _passwordController = TextEditingController();

  @override
  void dispose() {
    _loginController.dispose();
    _passwordController.dispose();
    super.dispose();
  }

  void _submit() {
    if (!_formKey.currentState!.validate()) {
      return;
    }
    ScaffoldMessenger.of(context).showSnackBar(
      SnackBar(content: Text('Вход: ${_loginController.text}')),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Вход')),
      body: Padding(
        padding: const EdgeInsets.all(16),
        child: Form(
          key: _formKey,
          child: Column(
            crossAxisAlignment: CrossAxisAlignment.stretch,
            children: [
              TextFormField(
                controller: _loginController,
                decoration: const InputDecoration(
                  labelText: 'Логин',
                  prefixIcon: Icon(Icons.person),
                ),
                validator: (v) =>
                    (v == null || v.trimisEmpty) ? 'Введите логин' : null,
              ),
              const SizedBox(height: 12),
              TextFormField(
                controller: _passwordController,
                obscureText: true,
                decoration: const InputDecoration(
                  labelText: 'Пароль',
                  prefixIcon: Icon(Icons.lock),
                ),
                validator: (v) =>
                    (v == null || v.length < 4) ? 'Минимум 4 символа' : null,
              ),
              const SizedBox(height: 24),
              FilledButton(
                onPressed: _submit,
                child: const Text('Войти'),
              ),
            ],
          ),
        ),
      ),
    );
  }
}