So im getting this error: "The argument type 'void Function(int)' can't be assigned to the parameter type 'Void Function()' " when I put add an argument into the function _answerQuestion(). So here is the main.dart file:

import 'package:flutter/material.dart';
import 'package:flutter_complete_guide/result.dart';

import 'quiz.dart';
import 'result.dart';

void main() => runApp(MyApp());

class MyApp extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    return _MyAppState();
  }
}

class _MyAppState extends State<MyApp> {
  final _questions = const [
    {
      'questionText': 'What\'s your favorite color?',
      'answers': [
        {'text': 'Black', 'score': 10},
        {'text': 'Red', 'score': 5},
        {'text': 'Green', 'score': 3},
        {'text': 'White', 'score': 1},
      ],
    },
    {
      'questionText': 'What\'s your favorite animal?',
      'answers': [
        {'text': 'Rabbit', 'score': 3},
        {'text': 'Snake', 'score': 11},
        {'text': 'Elephant', 'score': 5},
        {'text': 'Lion', 'score': 9},
      ],
    },
    {
      'questionText': 'Who\'s your favourite instructor?',
      'answers': [
        {'text': 'Max', 'score': 1},
        {'text': 'Max', 'score': 1},
        {'text': 'Max', 'score': 1},
        {'text': 'Max', 'score': 1},
      ],
    },
  ];

  int _questionIndex = 0;
  int _totalScore = 0;

  void _answerQuestion(int score) {
    _totalScore  = score;
    setState(() {
      _questionIndex = _questionIndex   1;
    });
    print(_questionIndex);
    if (_questionIndex < _questions.length) {
      print('We have more questions!');
    } else {
      print('No more questions');
    }
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
          appBar: AppBar(
            title: Text('My First App'),
          ),
          body: _questionIndex < _questions.length
              ? Quiz(
                  answerQuestion: _answerQuestion,
                  questionIndex: _questionIndex,
                  questions: _questions,
                )
              : Result()),
    );
  }
}

And here is the quiz.dart file:

import 'package:flutter/material.dart';

import 'question.dart';
import 'answer.dart';

class Quiz extends StatelessWidget {
  final List<Map<String, Object>> questions;
  int questionIndex;
  final VoidCallback answerQuestion;

  Quiz({
    required this.questions,
    required this.answerQuestion,
    required this.questionIndex,
  });

  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        Question(
          questions[questionIndex]['questionText'] as String,
        ),
        ...(questions[questionIndex]['answers'] as List<Map<String, Object>>)
            .map((answer) {
          return Answer(
            () => answerQuestion(answer['score']),
            answer['text'] as String,
          );
        }).toList()
      ],
    );
  }
}

And this is the answer.dart file:

import 'package:flutter/material.dart';

class Answer extends StatelessWidget {
  final VoidCallback selectHandler;
  final String answerText;

  Answer(this.selectHandler, this.answerText);

  @override
  Widget build(BuildContext context) {
    return Container(
      width: double.infinity,
      child: RaisedButton(
        color: Colors.blue,
        textColor: Colors.white,
        child: Text(answerText),
        onPressed: selectHandler,
      ),
    );
  }
}

If I remove the argument score on the function _answerQuestion everything will work just fine, but I soon as I add it I ll get that error. I have null safety turned off, sdk: ">=2.11.0 <3.0.0".

CodePudding user response：

Your Quiz widget is using final VoidCallback answerQuestion; and you cant have data on callback, use

  final Function(int) answerQuestion;