Questions example

main.dart

/*
 * Questions example
 * https://gist.github.com/PlugFox/66bca21faaaf8613857ade983c78a47b
 * https://dartpad.dev?id=66bca21faaaf8613857ade983c78a47b
 * Mike Matiunin <plugfox@gmail.com>, 13 January 2026
 */

// ignore_for_file: curly_braces_in_flow_control_structures, avoid_print

import 'dart:async';

import 'package:flutter/material.dart';

/// A unique identifier for a question.
typedef QuestionID = String;

/// A question with a unique [id], the question [text], and an optional [answer].
@immutable
class Question {
  const Question({required this.id, required this.text, required this.answer});

  const Question.unanswered({required this.id, required this.text})
    : answer = null;

  final QuestionID id;
  final String text;
  final bool? answer;
}

/// Record representing an answered question.
typedef Answer = ({QuestionID id, String text, bool answer});

/// A collection of [Question]s identified by their [QuestionID]s.
extension type Questions._(Map<QuestionID, Question> questions) {
  Questions(Iterable<Question> questions)
    : this._(<QuestionID, Question>{
        for (final question in questions) question.id: question,
      });

  /// Returns the next unanswered question, or `null` if all questions are answered.
  Question? get nextQuestion {
    for (final question in questions.values) {
      if (question.answer != null) continue;
      return question;
    }
    return null;
  }

  /// All questions in this collection.
  List<Answer> get answers => <Answer>[
    for (final question in questions.values)
      if (question case Question(:final id, :final text, :final answer?))
        (id: id, text: text, answer: answer),
  ];

  /// Answers the question with the given [id].
  void answer(QuestionID id, {required bool answer}) {
    if (questions[id] case final question?)
      questions[id] = Question(
        id: question.id,
        text: question.text,
        answer: answer,
      );
  }

  /// Resets all questions to unanswered.
  void reset() => questions.updateAll(
    (id, question) => Question.unanswered(id: question.id, text: question.text),
  );
}

void main() => runZonedGuarded<void>(
  () => runApp(const App()),
  (error, stackTrace) => print('$error'),
);

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

  @override
  Widget build(BuildContext context) => const MaterialApp(
    title: 'Questions',
    debugShowCheckedModeBanner: false,
    home: QuestionsScreen(),
  );
}

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

  @override
  State<QuestionsScreen> createState() => _QuestionsScreenState();
}

class _QuestionsScreenState extends State<QuestionsScreen> {
  final Questions _questions = Questions(<Question>[
    const Question.unanswered(id: 'q1', text: 'Is the sky blue?'),
    const Question.unanswered(id: 'q2', text: 'Is grass green?'),
    const Question.unanswered(id: 'q3', text: 'Is fire hot?'),
    const Question.unanswered(id: 'q4', text: 'Is water wet?'),
  ]);

  Question? _question;

  @override
  void initState() {
    super.initState();
    _question = _questions.nextQuestion;
  }

  void _answerQuestion(bool answer) {
    final question = _question;
    if (question == null) return;
    setState(() {
      _questions.answer(question.id, answer: answer);
      _question = _questions.nextQuestion;
    });
  }

  void _resetQuestions() {
    setState(() {
      _questions.reset();
      _question = _questions.nextQuestion;
    });
  }

  Widget _buildQuestion(Question question) => Column(
    key: ValueKey(question.id),
    mainAxisSize: MainAxisSize.min,
    mainAxisAlignment: MainAxisAlignment.center,
    crossAxisAlignment: CrossAxisAlignment.center,
    spacing: 16,
    children: <Widget>[
      Text(
        question.text,
        style: const TextStyle(fontSize: 24),
        textAlign: TextAlign.center,
      ),
      Row(
        mainAxisSize: MainAxisSize.min,
        mainAxisAlignment: MainAxisAlignment.center,
        crossAxisAlignment: CrossAxisAlignment.center,
        spacing: 16,
        children: <Widget>[
          ElevatedButton(
            onPressed: () => _answerQuestion(true),
            child: const Text('Yes'),
          ),
          ElevatedButton(
            onPressed: () => _answerQuestion(false),
            child: const Text('No'),
          ),
        ],
      ),
    ],
  );

  Widget _buildResults() => ListView(
    padding: const EdgeInsets.fromLTRB(16, 16, 16, 64),
    shrinkWrap: true,
    children: <Widget>[
      const Text(
        'Results',
        style: TextStyle(fontSize: 32, fontWeight: FontWeight.bold),
        textAlign: TextAlign.center,
      ),
      const SizedBox(height: 20),
      for (final (:id, :text, :answer) in _questions.answers)
        Center(
          child: SizedBox(
            width: 640,
            child: ListTile(
              key: ValueKey(id),
              title: Text(text),
              trailing: switch (answer) {
                true => const Icon(Icons.check, color: Colors.green),
                false => const Icon(Icons.close, color: Colors.red),
              },
            ),
          ),
        ),
    ],
  );

  @override
  Widget build(BuildContext context) => Scaffold(
    appBar: AppBar(
      title: const Text('Questions'),
      actions: <Widget>[
        IconButton(
          icon: const Icon(Icons.refresh),
          onPressed: _resetQuestions,
          tooltip: 'Reset Questions',
        ),
        const SizedBox(width: 8),
      ],
    ),
    body: SafeArea(
      child: Center(
        child: AnimatedSwitcher(
          duration: const Duration(milliseconds: 300),
          child: switch (_question) {
            Question question => _buildQuestion(question),
            null => _buildResults(),
          },
        ),
      ),
    ),
  );
}