CODEWITHSUNDEEP
flutterdart
samit
samit

Reputation: 108

Error: The argument type 'List<String>' can't be assigned to the parameter type 'String'

I am a beginner in dart and I am trying to make a quiz game application where I use some widgets to get questions and answer options on the screen. The error that I am facing is "The argument type 'List' can't be assigned to the parameter type 'String'" Here are some snippets of my code:-

  1. This is a list of Maps<String, Object> , I am storing questions and their answer options in this variable.
var questions = [
      {
        'questionText': 'What is your favourite season?',
        'answers': [
          'Summer',
          'Monsoon',
          'Winter',
        ]
      },
      {
        'questionText': 'What is your favourite color?',
        'answers': [
          'Black',
          'Green',
          'Blue',
        ]
      },
      {
        'questionText': 'What is your favourite food?',
        'answers': [
          'Chicken',
          'Kebab',
          'Biryani',
        ]
      },
    ];
  1. This is where I call the Question and Answer Widget.
body: Column(
          children: [
            Question(questions[_questionsIndex]["questionText"]),
            ...{questions[_questionsIndex]['answers'] as List<String>}
                .map((answer) {
              return Answer(_answerQuestion, answer); //**ERROR**
            }).toList(),
          ],
        ),

The error appears on the statement : return Answer(_answerQuestion, answer);

  1. This is how my Answer Widget Class looks like:
class Answer extends StatelessWidget {
  final Function selectAnswer;
  final String answerText;

  Answer(this.selectAnswer, this.answerText);

  @override
  Widget build(BuildContext context) {
    return Container(
      width: double.infinity,
      child: ElevatedButton(
        style: ElevatedButton.styleFrom(
          primary: Colors.blue,
          elevation: 0.0,
        ),
        child: Text(answerText,
            style: TextStyle(
              color: Colors.black,
            )),
        onPressed: () {
          selectAnswer();
        },
      ),
    );
  }
}

What is the meaning of this error and why does it appear? How can I fix this error?

Thank you!

Upvotes: 2

Views: 13800

Answers (4)

okoyeobi
okoyeobi

Reputation: 1

Instead of using List change it to var, it worked for me and the error disappeared is dynamic and works perfectly. This is my code below:

class _QuizPageState extends State<QuizPage> {

  var scoreKeeper = [
    Icon(
      Icons.check,
      color: Colors.green,
    ),
    Icon(
      Icons.close,
      color: Colors.red,
    ),
    Icon(
      Icons.close,
      color: Colors.red,
    ),
    Icon(
      Icons.check,
      color: Colors.green,
    ),
    Icon(
      Icons.close,
      color: Colors.red,
    ),

  ];

  @override
  Widget build(BuildContext context) {
    return Column(
      mainAxisAlignment: MainAxisAlignment.spaceBetween,
      crossAxisAlignment: CrossAxisAlignment.stretch,
      children: <Widget>[
        const Expanded(
          flex: 5,
          child: Padding(
            padding: EdgeInsets.all(10.0),
            child: Center(
              child: Text(
                'This is where the question text will go.',
                textAlign: TextAlign.center,
                style: TextStyle(
                  fontSize: 25.0,
                  color: Colors.white,
                ),
              ),
            ),
          ),
        ),
        Expanded(
          child: Padding(
            padding: EdgeInsets.all(15.0),
            child: TextButton(
              onPressed: (){

              },
              child: Text('True'),
              // color: Colors.white,
              style: TextButton.styleFrom(
                backgroundColor: Colors.white,
              ),
            ),
          ),
        ),
        Expanded(
          child: Padding(
            padding: EdgeInsets.all(15.0),
            child:TextButton(
              onPressed: (){

              },
              // color: Colors.white,
              style: TextButton.styleFrom(
                backgroundColor: Colors.pinkAccent,
              ),
              child: const Text('False'),
            ),
          ),
        ),
        Row(
          children: scoreKeeper,
        ),
      ],
    );
  }
}

Upvotes: 0

Ramy Wahid
Ramy Wahid

Reputation: 443

if you mean: The argument type 'List<String?>?' can't be assigned to the parameter type 'List<String?>'.

I solve this issue with a single line, you can get List<String?> from List<String?>?

List<String?>? mylist = ['data1','data2'];
List<String?> mylist2 = List<String>.from(mylist);

Upvotes: 4

Jos&#233; Zenteno
Jos&#233; Zenteno

Reputation: 1

You could try especifying the type of your main list with List<Map<String,dynamic>>

List<Map<String,dynamic>> questions = [
  {
    'questionText': 'What is your favourite season?',
    'answers': [
      'Summer',
      'Monsoon',
      'Winter',
    ]
  },
  {
    'questionText': 'What is your favourite color?',
    'answers': [
      'Black',
      'Green',
      'Blue',
    ]
  },
  {
    'questionText': 'What is your favourite food?',
    'answers': [
      'Chicken',
      'Kebab',
      'Biryani',
    ]
  },
];

I tried to assing the element to a List<String> and every works

var a = questions[1]['answers'];
List<String> b = a;
print(b);

Upvotes: 0

Zichzheng
Zichzheng

Reputation: 1280

I think the problem is in your second code block. For a list of string, you should use just List type Instead of List<String> type.

You code would be like:

body: Column(
          children: [
            Question(questions[_questionsIndex]["questionText"]),
            ...{questions[_questionsIndex]['answers'] as List}
                .map((answer) {
              return Answer(_answerQuestion, answer); //**ERROR**
            }).toList(),
          ],
        ),

I hope this can solve your problem.

Upvotes: 0

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