如何使用 flutter 中的小部件列出 map

Question

I want to have a normal questionare type of thing. As soon as the first question gets answered it should go to next question. But there was an error as 'type 'Null' is not a subtype of type 'List' in type cast' when I used.map(). The.map() and spread operator used to function in previous versions of flutter but now they are not.Can anyone please give a solution for this?

this is the following code-main.dart

class MyAppState extends State<MyApp> {
  int qindex = 0;

  void answeQues() {
    setState(() {
      qindex = qindex + 1;
    });

    print(qindex);
  }

  @override
  Widget build(BuildContext context) {
    var questions = [
      {
        'questionText': 'what\'s your favourite color?',
        'answers': ['R', 'G', 'B', 'Y']
      },
      {
        'questionText': 'what\'s your favourite animal?',
        ' answers': ['Rabbit', 'Giraffe', 'Bear', 'Yax']
      },
      {
        'questionText': 'what\'s your favourite sport?',
        'answers': ['Rugby', 'Cricket', 'Basketball', 'Football']
      },
    ];

    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('My first App'),
        ),
        body: Column(
          children: [
            Questions(
              questions[qindex]['questionText'].toString(),
            ),
            ...(questions[qindex]['answers'] as List<String>).map((answer) {
              return Answers(answeQues, answer);
            }).toList()

            // questions[qindex]['answers'].entries.map((answer) {
            //   return Answers(answeQues, answer);
            // }).toList()
          ],
        ),
      ),
    );
  }
}

this is my answers.dart file

import 'package:flutter/material.dart';

class Answers extends StatelessWidget {
  final Function selectHandler;
  final String answerText;

  Answers(this.selectHandler, this.answerText);
  @override
  Widget build(BuildContext context) {
    return Container(
      width: double.infinity,
      padding: EdgeInsets.all(10),
      child: RaisedButton(
        color: Colors.blue,
        child: Text(answerText),
        onPressed: () {
          selectHandler();
        },
      ),
    );
  }
}

Error:-

type 'Null' is not a subtype of type 'List' in type cast.

Answer 1

For your second question, you have space at the beginning of the key name ( ' answers' ), that causes the problem:

var questions = [
  ...
  {
    'questionText': 'what\'s your favourite animal?',
    ' answers': ['Rabbit', 'Giraffe', 'Bear', 'Yax']
  },
  ...
];

There is nothing wrong about.map() and spread operators, they are still used in Flutter.