import 'package:flutter/material.dart';

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

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

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(home: MyHomePage());
  }
}

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

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  final _formKey = GlobalKey<FormState>();

  bool? _withoutErrorBuilder;
  bool? _withErrorBuilder;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Form(
          key: _formKey,
          child: Column(
            mainAxisSize: MainAxisSize.min,
            children: [
              Text('Field without errorBuilder'),
              FormField<bool>(
                initialValue: _withoutErrorBuilder,
                validator: (value) {
                  debugPrint('[Without errorBuilder] validator was called with: $value');
                  return value == null ? 'Select an option' : null;
                },
                builder: (state) {
                  return RadioGroup<bool>(
                    groupValue: _withoutErrorBuilder,
                    onChanged: (value) {
                      setState(() => _withoutErrorBuilder = value);
                      state.didChange(value);
                    },
                    child: const Row(
                      children: [
                        Expanded(child: RadioListTile<bool>(title: Text('Option 1'), value: true)),
                        Expanded(child: RadioListTile<bool>(title: Text('Option 2'), value: false)),
                      ],
                    ),
                  );
                },
              ),

              SizedBox(height: 64),

              Text('Field with errorBuilder'),
              FormField<bool>(
                initialValue: _withErrorBuilder,
                validator: (value) {
                  debugPrint('[With errorBuilder] validator was called with: $value');
                  return value == null ? 'Select an option' : null;
                },
                errorBuilder: (context, errorText) {
                  debugPrint('[With errorBuilder] errorBuilder was called with: $errorText');
                  return Text(errorText, style: const TextStyle(fontSize: 12));
                },
                builder: (state) {
                  return RadioGroup<bool>(
                    groupValue: _withErrorBuilder,
                    onChanged: (value) {
                      setState(() => _withErrorBuilder = value);
                      state.didChange(value);
                    },
                    child: const Row(
                      children: [
                        Expanded(child: RadioListTile<bool>(title: Text('Option 1'), value: true)),
                        Expanded(child: RadioListTile<bool>(title: Text('Option 2'), value: false)),
                      ],
                    ),
                  );
                },
              ),

              const SizedBox(height: 36),
              ElevatedButton(
                onPressed: () {
                  final isValid = _formKey.currentState!.validate();

                  debugPrint('[Without errorBuilder] value: $_withoutErrorBuilder');
                  debugPrint('[With errorBuilder] value: $_withErrorBuilder');
                  debugPrint('Form is valid: $isValid');
                },
                child: const Text('Validate'),
              ),
            ],
          ),
        ),
      ),
    );
  }
}