CODEWITHSUNDEEP
androidstringflutterlistdart
Anurag Hale
Anurag Hale

Reputation: 143

Having problem in comparing String with a List element

I am trying to run an if-else condition that displays certain Icons based on the given conditions. I am trying to see if a particular quizId,i.e. a string is present inside the list to fulfill the condition. For some reason, the condition doesn't seem to work even though the element is present inside the list.

I have tried manually comparing the quizId with a particular String, which worked out fine. But as soon as I bring the list into the condition, it stops working. I have found both the quizId and List element data types which is String yet they still can't be compared.

This is the piece of Code :

class QuizBadge extends StatelessWidget {
  const QuizBadge({super.key, required this.topic, required this.quizId});

  final Topic topic;
  final String quizId;

  @override
  Widget build(BuildContext context) {
    Report report = Provider.of<Report>(context);
    List completed = report.topics.values.toList();

    List a = completed.expand((element) => element).toList();
    print(a[1]);

    if (a[1] == "flutter-basics") {
      return const Icon(FontAwesomeIcons.checkDouble, color: Colors.green);
    } else {
      return const Icon(FontAwesomeIcons.solidCircle, color: Colors.grey);
    }
  }
}

Any help would be appreciated. Thank You.

Edited Code Piece :

  Widget build(BuildContext context) {
    Report report = Provider.of<Report>(context);

    List completed = report.topics[topic.id] ?? [];
    String str = completed.map((e) => e.toString()).join('-');

    if (str.contains(quizId)) {
      return const Icon(FontAwesomeIcons.checkDouble, color: Colors.green);
    } else {
      return const Icon(FontAwesomeIcons.solidCircle, color: Colors.grey);
    }
  }

This seems to be working.

Upvotes: 2

Views: 67

Answers (1)

Chuck Batson
Chuck Batson

Reputation: 2774

This is occurring because the elements in your list are not strings. Consider checking the type returned by report.topics.values.toList() (I can't tell because you didn't include this) and/or explicitly declare the lists you expect to be strings as List<String>, for example:

    List<String> a = completed.expand((element) => element).toList();

You will see an error on that line if you declare it this way, and the error will offer a clue.

In general, I prefer to avoid using generics without specifying an explicit type, because the default is dynamic, and you don't get the benefit of static type checking. You can also maintain explicit typing by using var/final declarations, such as:

    var a = completed.expand((element) => element).toList();

Follow-Up

void main() {
  var completed = [["firestore-basics"], ["flutter-basics"], ["js-basics", "js-variables"], ["rxjs-basics"]];
  var a = completed.expand((element) => element).toList();
  print(a);
  bool contains = a.contains('flutter-basics');
  print('contains? = $contains');
}

Output:

[firestore-basics, flutter-basics, js-basics, js-variables, rxjs-basics]
contains? = true

Upvotes: 1

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