ฟอร์ม: TextField คอนโทรลเลอร์ และการตรวจสอบความถูกต้อง

import 'package:flutter/material.dart';

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

  @override
  State<NicknameField> createState() =>
      _NicknameFieldState();
}

class _NicknameFieldState extends State<NicknameField> {
  final _controller = TextEditingController();

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return TextField(
      controller: _controller,
      decoration: const InputDecoration(
        labelText: 'Nickname',
        border: OutlineInputBorder(),
      ),
      onSubmitted: (value) => debugPrint(value),
    );
  }
}

import 'package:flutter/material.dart';

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

  @override
  State<SignUpForm> createState() => _SignUpFormState();
}

class _SignUpFormState extends State<SignUpForm> {
  final _formKey = GlobalKey<FormState>();
  final _emailController = TextEditingController();

  @override
  void dispose() {
    _emailController.dispose();
    super.dispose();
  }

  void _submit() {
    if (_formKey.currentState!.validate()) {
      debugPrint('Email: ${_emailController.text}');
    }
  }

  @override
  Widget build(BuildContext context) {
    return Form(
      key: _formKey,
      child: Column(
        mainAxisSize: MainAxisSize.min,
        children: [
          TextFormField(
            controller: _emailController,
            keyboardType: TextInputType.emailAddress,
            decoration: const InputDecoration(
              labelText: 'Email',
            ),
            validator: (value) {
              if (value == null || value.isEmpty) {
                return 'Required field';
              }
              if (!value.contains('@')) {
                return 'Invalid address';
              }
              return null;
            },
          ),
          const SizedBox(height: 16),
          FilledButton(
            onPressed: _submit,
            child: const Text('Create account'),
          ),
        ],
      ),
    );
  }
}