The String of an instance of a class becomes null. why? (dart flutter)

Question

When I print q1 it's null. I expected to see the question printed.

void main() {
  Question q1 = Question(
      q: 'You can lead a cow down stairs but not up stairs.', a: false);

  print(q1.questionAnswer);

}

class Question {
  String questionText;
  bool questionAnswer;
  Question({String q, bool a}) {
    q = questionText;
    a = questionAnswer;
  }
}

Solution 1

Just try changing your constructor to

Question({String q, bool a}) {
    questionText = q;
    questionAnswer = a;
  }

Default value of any instance variable in dart will always be null.

So, in your case value of questionText and questionAnswer will also be null as everything in dart is an Object.

Solution 2

Another way you can do this is by using the this keyword

class Question {
 String questionText;
 bool questionAnswer;

 Question({this.questionText, this.questionAnswer});
}

and then use it like this

void main() {
  Question q1 = Question(questionText: 'question text', questionAnswer: false);

  print(q1.questionAnswer);
}

here is the dart pad

Comments

[Maxim Sagaydachny]

Should not you assign members instead of parameters? I mean questionText = q; questionAnswer = a;