CODEWITHSUNDEEP
flutterdart
rasal
rasal

Reputation: 39

What is necessary the propagation operator(...), in this code flutter

I get this error when I attempt to compile:

The element type 'Iterable' can't be assigned to the list type 'Widget'.dartlist_element_type_not_assignable.

My code:

import 'package:flutter/material.dart';

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

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

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

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

  void _answerQuestion() {
    setState(() {
      _questionIndex = _questionIndex + 1;
      print(_questionIndex);
    });
  }

  @override
  Widget build(BuildContext context) {
    var questions = [
      {
        'question': 'what is your favourite color',
        'answers': ['Black', 'Red', 'Green', 'white']
      },
      {
        'question': 'what is your favourite song',
        'answers': ['Thunderstorm', 'AC/DC', 'Mama mia', 'Burriqio']
      },
      {
        'question': 'what is your favourite food',
        'answers': ['Macarrones', 'Salmorejo', 'Albondigas', 'Chorizo']
      }
    ];

    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('My First App'),
        ),
        body: Column(
          children: [
            Question(
              questions[_questionIndex]['question'],
            ),
            ...(questions[_questionIndex]['answers'] as List<String>).map((answer) {
              return Answer(_answerQuestion, answer);
            })
          ],
        ),
      ),
    );
  }
}

I don't understand why I have to use that for add to list. Because isn't the operator for creating a new list with each element mapping with the method map?

Thank you if you can help me.

Upvotes: 0

Views: 58

Answers (1)

Jaecheol Park
Jaecheol Park

Reputation: 702

If you don't use spread operator(...), the result is nested list in your code.

Like below.

body: Column(
  children: [
    Widget1,
    [Widget2, Widget3, ...],
  ],
),

When you use spread operator, the result will be list of Widget.

body: Column(
  children: [
    Widget1,
    ...[Widget2, Widget3, ...],
  ],
),

is same with below.

body: Column(
  children: [
    Widget1,
    Widget2,
    Widget3, 
    ...,
  ],
),

Upvotes: 1

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