CODEWITHSUNDEEP
firebaseflutterdart
Goldlightdrake
Goldlightdrake

Reputation: 183

Future function was called on null (Flutter)

So I'm writing an quiz app and I need to get defined amount of questions from firestore. So i created two files data provider file and repository file, and that's how they look: Data Provider

class TestProvider {
  FirebaseFirestore _firestore = FirebaseFirestore.instance;

  Future<Map> getQuestionFromFirebase(String documentId) async {
    Map mappedQuestion;
    await _firestore
        .collection('questions')
        .doc(documentId)
        .get()
        .then((DocumentSnapshot snapshot) => mappedQuestion = snapshot.data());
    return mappedQuestion;
  }
}

Repository

class TestRepository {
  final int amountOfQuestions;
  TestRepository({
    @required this.amountOfQuestions,
  });

  TestProvider _testProvider;

  Future listOfQuestions() async {
    List<int> range = numberInRange(amountOfQuestions);
    List<Question> listOfQuestions;
    for (int i = 1; i <= amountOfQuestions; i++) {
      listOfQuestions.add(Question.fromMap(
          await _testProvider.getQuestionFromFirebase(range[i].toString())));
    }
    return listOfQuestions;
  }
}

The error i get:

E/flutter ( 5186): [ERROR:flutter/lib/ui/ui_dart_state.cc(177)] Unhandled Exception: NoSuchMethodError: The method 'getQuestionFromFirebase' was called on null.
E/flutter ( 5186): Receiver: null
E/flutter ( 5186): Tried calling: getQuestionFromFirebase("3")

The funny thing about it is the fact that when i call fuction from provider i don't get error. Problem begins when I'm using it from repo class. Any idea how to fix it? I don't want to use FutureBuilder any time I want to use it in widget. I want to transform snapshot into my question model.

Upvotes: 0

Views: 34

Answers (1)

Marcos Boaventura
Marcos Boaventura

Reputation: 4741

In your TestRepository code it's not clear where you are instantiating TestProvider _testProvider; member.

The error message is clear The method 'getQuestionFromFirebase' was called on null. So there is no instance of TestProvider class and _testProvider is a null pointer.

Grant TestProvider _testProvider = TestProvider(); in your code as said by @ikerfah and you will have no issues in your code.

Upvotes: 1

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