multi choice quiz

QuizPage.kotlin

class QuizPage extends StatefulWidget {
  @override
  _QuizPageState createState() => _QuizPageState();
}

class _QuizPageState extends State<QuizPage> {
  int _currentQuestionIndex = 0;
  List<QuizQuestion> _questions = [    QuizQuestion(      question: 'What is the capital of France?',      answers: ['Paris', 'London', 'New York', 'Tokyo'],
      correctAnswer: 'Paris',
    ),
    QuizQuestion(
      question: 'What is the tallest mountain in the world?',
      answers: ['Mount Everest', 'K2', 'Kilimanjaro', 'Annapurna'],
      correctAnswer: 'Mount Everest',
    ),
    // more quiz questions...
  ];
  Map<String, bool> _answers = {};

  void _submitAnswers() {
    int numCorrect = 0;
    _questions.forEach((question) {
      if (_answers[question.question] == question.correctAnswer) {
        numCorrect++;
      }
    });
    // show the results
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Column(
        children: [
          Text(_questions[_currentQuestionIndex].question),
          ..._questions[_currentQuestionIndex].answers.map((answer) {
            return RadioListTile(
              value: answer,
              title: Text(answer),
              groupValue: _answers[_questions[_currentQuestionIndex].question],
              onChanged: (newValue) {
                setState(() {
                  _answers[_questions[_currentQuestionIndex].question] = newValue;
                });
              },
            );
          }),
          RaisedButton(
            onPressed: _currentQuestionIndex < _questions.length - 1
                ? () {
                    setState(() {
                      _currentQuestionIndex++;
                    });
                  }
                : _submitAnswers,
            child: Text(_currentQuestionIndex <