Here is the code for a Quiz App I have been making. This is the main.dart file.

import 'package:flutter/material.dart';
import 'list.dart';

void main() {
  runApp(
    const Quizzler(),
  );
}

class Quizzler extends StatefulWidget {
  const Quizzler({Key? key}) : super(key: key);

  @override
  State<Quizzler> createState() => _QuizzlerState();
}

class _QuizzlerState extends State<Quizzler> {
  List<Widget> scoreKeeper = [];
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        backgroundColor: Colors.black,
        body: Column(
          crossAxisAlignment: CrossAxisAlignment.stretch,
          children: [
            Expanded(
              flex: 6,
              child: Padding(
                padding: const EdgeInsets.all(32.0),
                child: Center(
                  child: Text(
                    Quiz().getQuestion(),
                    style: const TextStyle(
                      color: Colors.white,
                      fontSize: 20,
                    ),
                    textAlign: TextAlign.center,
                  ),
                ),
              ),
            ),
            boolButton(Colors.green, 'True'),
            boolButton(Colors.red, 'False'),
            Row(
              children: scoreKeeper,
            ),
          ],
        ),
      ),
    );
  }

  Expanded boolButton(Color c, String s) {
    return Expanded(
      child: Padding(
        padding: const EdgeInsets.all(8.0),
        child: ElevatedButton(
          style: ButtonStyle(
            backgroundColor: MaterialStateProperty.all(c),
          ),
          onPressed: () {
            setState(
              () {
                switcher(s);
                Quiz().nextQuestion();
              },
            );
          },
          child: Text(
            s,
          ),
        ),
      ),
    );
  }

  switcher(String s) {
    if (Quiz().getAnswer().toLowerCase() == s.toLowerCase()) {
      scoreKeeper.add(
        const Icon(
          Icons.check,
          color: Colors.green,
        ),
      );
    } else {
      scoreKeeper.add(
        const Icon(
          Icons.close,
          color: Colors.red,
        ),
      );
    }
  }
}

This is the list.dart file that I imported onto the main.dart file:

import 'question.dart';

class Quiz {
  int _counter = 0;

  final List<Question> _q = [
    Question(
      'Cows can only be lead up a flight of stairs and not down.',
      'False',
    ),
    Question(
      'Approximately one quarter of human bones are in the feet.',
      'True',
    ),
    Question(
      'A slug\'s blood is green.',
      'True',
    ),
  ];

  void nextQuestion() {
    _counter  ;
  }

  String getQuestion() {
    return _q[_counter].question;
  }

  String getAnswer() {
    return _q[_counter].answer;
  }
}

And this is the question.dart file that I imported onto the list.dart file:

class Question {
  String question;
  String answer;
  Question(this.question, this.answer);
}

In the Quiz app, once I hit True or False it just shows a tick for the right answer (False) and a cross for the wrong answer (True), without moving to the next question. How do I fix this?

CodePudding user response：

Here, you call any variables or methods from Quiz class by calling directly by Quiz(), basically problems occur here.

By calling Quiz() every time you created a new object, there is no tracking of this object. Because you don't save the object.

So, at first, save the object like that...

Quiz quiz = Quiz();  

then wherever you call by Quiz(), replace by quiz. be like..... quiz.getQuestion(),quiz.nextQuestion(),quiz.getAnswer()
I add all three dart file added below ... with the solution of showing a ques ending alert snackbar.


This is the main.dart file.

import 'package:flutter/material.dart';
import 'list.dart';

void main() {
  runApp(
    const Quizzler(),
  );
}

class Quizzler extends StatefulWidget {
  const Quizzler({Key? key}) : super(key: key);

  @override
  State<Quizzler> createState() => _QuizzlerState();
}

class _QuizzlerState extends State<Quizzler> {

  /// This is for show snack bar
  final _messangerKey = GlobalKey<ScaffoldMessengerState>();

  Quiz quiz = Quiz();

  List<Widget> scoreKeeper = [];
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      scaffoldMessengerKey: _messangerKey,
      home: Scaffold(
        backgroundColor: Colors.black,
        body: Column(
          crossAxisAlignment: CrossAxisAlignment.stretch,
          children: [
            Expanded(
              flex: 6,
              child: Padding(
                padding: const EdgeInsets.all(32.0),
                child: Center(
                  child: Text(
                    quiz.getQuestion(),
                    style: const TextStyle(
                      color: Colors.white,
                      fontSize: 20,
                    ),
                    textAlign: TextAlign.center,
                  ),
                ),
              ),
            ),
            boolButton(Colors.green, 'True'),
            boolButton(Colors.red, 'False'),
            Row(
              children: scoreKeeper,
            ),
          ],
        ),
      ),
    );
  }

  Expanded boolButton(Color c, String s) {
    return Expanded(
      child: Padding(
        padding: const EdgeInsets.all(8.0),
        child: ElevatedButton(
          style: ButtonStyle(
            backgroundColor: MaterialStateProperty.all(c),
          ),
          onPressed: () {
            (quiz.q.length - 1) > quiz.counter ? setState(
                  () {
                switcher(s);
                quiz.nextQuestion();
              },
            ) : _messangerKey.currentState!.showSnackBar(
                const SnackBar(duration: Duration(seconds : 2),content: Text('No more questions')));
          },
          child: Text(
            s,
          ),
        ),
      ),
    );
  }

  switcher(String s) {
    if (quiz.getAnswer().toLowerCase() == s.toLowerCase()) {
      scoreKeeper.add(
        const Icon(
          Icons.check,
          color: Colors.green,
        ),
      );
    } else {
      scoreKeeper.add(
        const Icon(
          Icons.close,
          color: Colors.red,
        ),
      );
    }
  }
}

This is the list.dart file

import 'question.dart';

class Quiz {
  int counter = 0;

  final List<Question> q = [
    Question(
      'Cows can only be lead up a flight of stairs and not down.',
      'False',
    ),
    Question(
      'Approximately one quarter of human bones are in the feet.',
      'True',
    ),
    Question(
      'A slug\'s blood is green.',
      'True',
    ),
  ];

  void nextQuestion() {
    counter  ;
  }

  String getQuestion() {
    return q[counter].question;
  }

  String getAnswer() {
    return q[counter].answer;
  }
}

And this is the question.dart file

class Question {
  String question;
  String answer;
  Question(this.question, this.answer);
}