Question 184842 in Flutter Question posted in
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Flutter – Non-nullable instance field '_cardResults' must be initialized

I get this error after writing this code. Non-nullable instance field ‘_cardResults’ must be initialized.
Try adding an initializer expression, or add a field initializer in this constructor, or mark it. When I try to add the late initializer and run it I get another error: LateInitializationError: Field ‘_cardResults’ has not been initialized.

import 'dart:async';
import 'package:rxdart/rxdart.dart';
import 'package:flutter/services.dart' show rootBundle;
import 'dart:convert';
import '../../helpers/card_colors.dart';
import '../../models/credit card/card_model.dart';

class CardListBloc {
final BehaviorSubject<List<CardResults>> _cardsCollection =
  BehaviorSubject<List<CardResults>>();

List<CardResults> _cardResults;

//Retrieve data from Stream
Stream<List<CardResults>> get cardList => _cardsCollection.stream;

void initialData() async {
var initialData = await rootBundle.loadString('data/initialData.json');
var decodedJson = jsonDecode(initialData);
_cardResults = CardModel.fromJson(decodedJson).results;
for (var i = 0; i < _cardResults.length; i++) {
  _cardResults[i].cardColor = CardColor.baseColors[i];
}
_cardsCollection.sink.add(_cardResults);
}

 CardListBloc() {
initialData();
}

void addCardToList(CardResults newCard) {
_cardResults.add(newCard);
_cardsCollection.sink.add(_cardResults);
}

void dispose() {
_cardsCollection.close();
}
}

final cardListBloc = CardListBloc();
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2

Answers


  1. Chosen as BEST ANSWER
    0

    i fixed this problem by adding this._cardResult and calling empty list in final cardList like so:

    CardListBloc(this._cardResults) {

initialData();
 }
 final cardListBloc = CardListBloc([]);

  2. 0

    The problem is that you’re trying to access the _cardResults field, which is a non-nullable instance field before it has been initialized. In Dart, non-nullable instance fields must be initialized before they can be used.

    To resolve this issue, you can either initialize the _cardResults field when it’s declared or initialize it in the constructor. let me show you an example of initializing it in the constructor:

    class CardListBloc {
  final BehaviorSubject<List<CardResults>> _cardsCollection =
      BehaviorSubject<List<CardResults>>();

  List<CardResults> _cardResults;

  // Retrieve data from Stream
  Stream<List<CardResults>> get cardList => _cardsCollection.stream;

  void initialData() async {
    var initialData = await rootBundle.loadString('data/initialData.json');
    var decodedJson = jsonDecode(initialData);
    _cardResults = CardModel.fromJson(decodedJson).results;
    for (var i = 0; i < _cardResults.length; i++) {
      _cardResults[i].cardColor = CardColor.baseColors[i];
    }
    _cardsCollection.sink.add(_cardResults);
  }

  CardListBloc() {
    _cardResults = []; // Initialize your field here...
    initialData();
  }

  void addCardToList(CardResults newCard) {
    _cardResults.add(newCard);
    _cardsCollection.sink.add(_cardResults);
  }

  void dispose() {
    _cardsCollection.close();
  }
}

final cardListBloc = CardListBloc();

    In my example above, the _cardResults field is initialized as an empty list in the constructor before calling the initialData() method. This ensures that the field is initialized before it’s used.

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