Flutter, bug in classes - flutter

Question

In main.dart I call Quiz's function getQuestionText and getQuestionAnswer, getQuestionText works as expected but the other doesn't work, if returns me always the first result of the list. I just placed a debugPrint() and as expected getQuestionText() prints the correct number, getQuestionAnswer() always print 0, how is that possible?
class Quiz {
int _questionNumber = 0;
List<Question> _questions = [
Question('Some cats are actually allergic to humans', true),
Question('You can lead a cow down stairs but not up stairs.', false),
];
void nextQuestion() {
if (_questionNumber < _questions.length - 1) {
_questionNumber++;
}
}
String getQuestionText() {
print('$_questionNumber'); // <-- print the correct number
return _questions[_questionNumber].questionText;
}
bool getQuestionAnswer() {
print('$_questionNumber'); // <-- always print 0
return _questions[_questionNumber].questionAnswer;
}
}
Here how I call the functions
void checkAnswer(bool userAnswer) {
bool correctAnswer = Quiz().getQuestionAnswer();
setState(() {
if (userAnswer == correctAnswer) {
// right answer
} else {
// wrong pick
);
}
quiz.nextQuestion();
});
}

Answer 1

The problem is that you always create a fresh instance of your class Quiz by calling bool correctAnswer = Quiz().getQuestionAnswer(); inside checkAnswer().
Try to store the Quiz instance ouside:
const myQuiz = Quiz();
void checkAnswer(bool userAnswer) {
bool correctAnswer = myQuiz.getQuestionAnswer();
setState(() {
if (userAnswer == correctAnswer) {
// right answer
} else {
// wrong pick
}
myQuiz.nextQuestion();
});
}