dart - I have problem Creating a list and constructor in Flutter

I have 3 Lists in my Flutter Project; How can I collect them in one list using Class and constructor in Flutter ?

my three lists;

one has three question
second has image
third has true or false

I want to collect them in one list.

I tried:

class Question {
  late String questionText; 
  late String questionImage; 
  late bool questionAnswer; 

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

it shows error in this line

I have 3 Lists in my Flutter Project; How can I collect them in one list using Class and constructor in Flutter ?

my three lists;

one has three question
second has image
third has true or false

I want to collect them in one list.

I tried:

class Question {
  late String questionText; 
  late String questionImage; 
  late bool questionAnswer; 

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

it shows error in this line

Share Improve this question edited Feb 18 at 4:21 Ruchit 2,7301 gold badge14 silver badges27 bronze badges asked Feb 17 at 22:43 Mostafa Ismael 192 bronze badges New contributor Mostafa Ismael is a new contributor to this site. Take care in asking for clarification, commenting, and answering. Check out our Code of Conduct.

1 Can you include the code? All I see is some text, but no code. It sounds like you want a List<SomeItem> where SomeItem is a class with three properties: String question, image, and bool. – Randal Schwartz Commented Feb 17 at 22:51
class Question { late String questionText; late String questionImage; late bool questionAnswer; Question({String q, String i, bool a}) { questionText = q; questionImage = i; questionAnswer = a; } } – Mostafa Ismael Commented Feb 17 at 23:15
1 Keep reading the standard dart documentation. Your constructor should be using "this.questionText" and so on. – Randal Schwartz Commented Feb 18 at 0:28
As Randal said in his first comment, you'll need List<Question> to represent the list. If you're having problems creating the list, show the code you tried (click the edit link under your question to edit it) and the error you get. – Frank van Puffelen Commented Feb 18 at 2:40

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1 Answer 1

Sorted by: Reset to default 3

You can implement your class like this:

class Question {
  late String? questionText;
  late String? questionImage;
  late bool? questionAnswer;

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

Here, you may even remove the late modifiers to the class instance variables. If you decide to also remove the required keyword, a null check may be necessary during manipulation of the values (also needed for when instance variable typed as nullable e.g. String?).

You can use the class to collect and the information like this:

class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key});

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  Question myQuestion = Question(
    questionText: "Is this a question?",
    questionImage: "path/to/image.png",
    questionAnswer: false,
  );

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text("Example")),
      body: SingleChildScrollView(
        child: Padding(
          padding: EdgeInsets.all(20.0),
          child: Column(
            children: [
              Text("QT: ${myQuestion.questionText}"),
              Text("QI: ${myQuestion.questionImage}"),
              Text("QA: ${myQuestion.questionAnswer}"),
            ],
          ),
        ),
      ),
    );
  }
}

The full code for the demo example:

import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatefulWidget {
  const MyApp({super.key});

  @override
  State<MyApp> createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(home: const MyHomePage());
  }
}

class Question {
  late String? questionText;
  late String? questionImage;
  late bool? questionAnswer;

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

class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key});

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  Question myQuestion = Question(
    questionText: "Is this a question?",
    questionImage: "path/to/image.png",
    questionAnswer: false,
  );

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text("Example")),
      body: SingleChildScrollView(
        child: Padding(
          padding: EdgeInsets.all(20.0),
          child: Column(
            children: [
              Text("QT: ${myQuestion.questionText}"),
              Text("QI: ${myQuestion.questionImage}"),
              Text("QA: ${myQuestion.questionAnswer}"),
            ],
          ),
        ),
      ),
    );
  }
}

Hope this helps.

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