checkbox_group_form.dart

import 'package:flutter/material.dart';

final Color darkBlue = Color.fromARGB(255, 18, 32, 47);

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData.dark().copyWith(scaffoldBackgroundColor: darkBlue),
      debugShowCheckedModeBanner: false,
      home: Home(),
    );
  }
}

class Home extends StatelessWidget {
  Home({Key? key}) : super(key: key);

  final List<CheckBoxClass> list = [
    CheckBoxClass('Ok', false),
    CheckBoxClass('No', false),
  ];

  final GlobalKey<FormState> formKey = GlobalKey<FormState>();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        actions: [
          IconButton(
              icon: Icon(Icons.save),
              onPressed: () {
                formKey.currentState?.validate();
              })
        ],
      ),
      body: Center(
        child: Form(
          key: formKey,
          child: FormField<List<bool>>(
            validator: (value) {
              final _list = value?.where((element) => element).toList();
              if (_list?.isEmpty ?? true) {
                return 'Please choose one';
              }
            },
            builder: (state) => Column(
              children: [
                Wrap(
                  children: List.generate(
                    list.length,
                    (index) {
                      final item = list[index];
                      return Padding(
                        padding: const EdgeInsets.all(8.0),
                        child: CheckboxListTile(
                          title: Text(item.text),
                          value: state.value?[index] ?? false,
                          onChanged: (value) {
                            list[index].val = value!;
                            final _list = list.map<bool>((e) => e.val).toList();
                            state.didChange(_list);
                          },
                        ),
                      );
                    },
                  ),
                ),
                if (state.hasError) Text(state.errorText ?? ''),
              ],
            ),
          ),
        ),
      ),
    );
  }
}

class CheckBoxClass {
  final String text;
  bool val;

  CheckBoxClass(this.text, this.val);
}