I'm trying to set the score from list but flutter is showing me null safety issue-CodePudding

I can't get rid of null safety and whenever I run this code it shows me that you're trying to expect List but you get List<String, Widget>. Actually, I'm new here, so the way I'm asking might not be good..... but I really need to solve this problem...Thankx

This is answer file (answer.dart):

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(
      child: RaisedButton(
        child: Text(answerText),
        onPressed: selectHandler,
        color: Colors.amber,
      ),
      margin: EdgeInsets.all(10),
      width: double.infinity,
    );
  }
}

This is quiz file (quiz.dart):

import 'package:flutter/material.dart';
import './question.dart';
import './answer.dart';


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

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

  @override
  Widget build(BuildContext context) {
    return Container(
      child: Column(
        children: [
          Question(questions[questionIndex]["questionText"] as String),
          ...(questions[questionIndex]["answerText"]["text"] as List<String>)
              .map((answer) {
            return Answer(answerQuestion, answer);
          }).toList(),
        ],
      ),
      alignment: Alignment.center,
    );
  }
}

This is for showing result (result.dart):

import 'package:flutter/material.dart';

class Result extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
    return Center(child: Text("You did it!"));
  }
}

This is for questions (question.dart):

import 'package:flutter/material.dart';

class Question extends StatelessWidget {
  final String questionText;

  Question(this.questionText);

  @override
  Widget build(BuildContext context) {
    return Container(
      child: Text(
        questionText,
        style: TextStyle(
          fontSize: 30,
        ),
        textAlign: TextAlign.center,
      ),
      width: double.infinity,
      margin: EdgeInsets.all(10),
    );
  }
}

This is main file (main.dart):

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

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

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

class _MyAppState extends State<MyApp> {
  int _totalScore = 0;
  var _questionIndex = 0;

  //some random questions
  var _questions = [
    {
      "questionText":
          "What year was the first Iron Man movie released, kicking off the Marvel Cinematic Universe?",
      "answerText": [
        {"text": "2005", "score": 5},
        {"text": "2008", "score": 6},
        {"text": "2010", "score": 7},
        {"text": "2012", "score": 8},
      ]
    },
    {
      "questionText": "What is the name of Thor’s hammer?",
      "answerText": [
        {"text": "Vanir", "score": 5},
        {"text": "Mjolnir", "score": 6},
        {"text": "Aesir", "score": 7},
        {"text": "Norn", "score": 8},
      ],
    },
    {
      "questionText":
          "In the Incredible Hulk, what does Tony tell Thaddeus Ross at the end of the film?",
      "answerText": [
        {"text": "That he wants to study The Hulk", "score": 5},
        {"text": "That he knows about S.H.I.E.L.D", "score": 6},
        {"text": "That they are putting a team together", "score": 7},
        {"text": "That Thaddeus owes him money", "score": 8},
      ],
    },
    {
      "questionText":
          "The Flerkens are a race of extremely dangerous aliens that resembles what?",
      "answerText": [
        {"text": "Cats", "score": 5},
        {"text": "Ducks", "score": 6},
        {"text": "Reptiles", "score": 7},
        {"text": "Raccoons", "score": 8},
      ],
    },
    {
      "questionText":
          "Before becoming Vision, what is the name of Iron Man’s A.I. butler?",
      "answerText": [
        {"text": "H.O.M.E.R.", "score": 5},
        {"text": "J.A.R.V.I.S.", "score": 6},
        {"text": "A.L.F.R.E.D.", "score": 7},
        {"text": "M.A.R.V.I.N.", "score": 8},
      ],
    },
    {
      "questionText": "What's the real name of the Blank Panther?",
      "answerText": [
        {"text": "T’Challa", "score": 5},
        {"text": "M’Baku", "score": 6},
        {"text": "N’Jadaka", "score": 7},
        {"text": "N’Jobu", "score": 8},
      ]
    },
    {
      "questionText":
          "What is the alien race Loki sends to invade Earth in The Avengers?",
      "answerText": [
        {"text": "The Chitauri", "score": 5},
        {"text": "The Skrulls", "score": 6},
        {"text": "The Kree", "score": 7},
        {"text": "The Flerkens", "score": 8},
      ],
    },
    {
      "questionText":
          "Who was the last holder of the Space Stone before Thanos claims it for his Infinity Gauntlet?",
      "answerText": [
        {"text": "Thor", "score": 5},
        {"text": "Loki", "score": 6},
        {"text": "The Collector", "score": 7},
        {"text": "Tony Stark", "score": 8},
      ],
    },
    {
      "questionText":
          "What fake name does Natasha use when she first meets Tony?",
      "answerText": [
        {"text": "Natalie Rushman", "score": 5},
        {"text": "Natalia Romanoff", "score": 6},
        {"text": "Nicole Rohan", "score": 7},
        {"text": "Naya Rabe", "score": 8},
      ]
    }
  ];

  void _answerQuestion(int score) {

    _totalScore  = score;

    setState(() {
      //preventing app from exceeding range, so it won't crash
      if (_questionIndex < _questions.length) {
        _questionIndex  ;
      }
    });

    print("Answer Choosen!");
    print(_totalScore);
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text("Flutter App"),
          centerTitle: true,
          backgroundColor: Colors.black87,
        ),
        body: (_questionIndex < _questions.length)
            ? Quiz(
                answerQuestion:() => _answerQuestion(2),
                questions: _questions,
                questionIndex: _questionIndex)
            : Center(
                child: Text(
                  "You did it!",
                  style: TextStyle(fontSize: 40),
                ),
              ),
      ),
    );
  }
}

CodePudding user response：

var _questions = [
    {
      "questionText":
          "What year was the first Iron Man movie released, kicking off the Marvel Cinematic Universe?",
      "answerText": [
        {"text": "2005", "score": 5},
        {"text": "2008", "score": 6},
        {"text": "2010", "score": 7},
        {"text": "2012", "score": 8},
      ]
    }
];

According to your _questions data, (in your Quiz class) questions[questionIndex]["answerText"] should be a List<Object> and answer should be a Map<String, Object> and then you can extract the answer text from the answerMap.

class Quiz extends StatelessWidget {

  final VoidCallback answerQuestion;
  final List<Map<String, Object>> questions;
  final int questionIndex;

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

  @override
  Widget build(BuildContext context) {
    return Container(
      child: Column(
        children: [
          Question(questions[questionIndex]["questionText"] as String),
          ...(questions[questionIndex]["answerText"] as List<Object>)
              .map((answer) {
               var answerMap = answer as Map<String, Object>;
            return Answer(answerQuestion, answerMap['text'] as String);
          }).toList(),
        ],
      ),
      alignment: Alignment.center,
    );
  }
}