flutter dynamic Checkboxes don't check

Question

Hi im new to Flutter and coding and tried do build my first to do app. I've created a textformfield to add new todos with a button in a container above. By pressing a button, a new todo will appear on the todo Container. I managed to dynamically give a column new todos with a CheckboxListtTitle. However, when adding a new todo, the todo with a checkbox appears but can't be checked. What did I do wrong here?

to_do_section.dart

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:flutter/src/foundation/key.dart';
import 'package:flutter/src/widgets/framework.dart';
import 'package:flutter_application_1/presentation/widgets/landing_page.dart';
import 'package:flutter_application_1/responsive_layout.dart';
import 'package:flutter/scheduler.dart' show timeDilation;

var toDoList = <String>[userInput];

class ToDos extends StatefulWidget {
  final List<String> list;
  const ToDos({
    Key? key,
    required this.list,
  }) : super(key: key);

  @override
  State<ToDos> createState() => _ToDosState();
}

class _ToDosState extends State<ToDos> {
  @override
  Widget build(BuildContext context) {
    SizeConfig().init(context);
    bool checked= false;
    bool? value_1;
    var isSelected = [false, false];

    return StatefulBuilder(
        builder: (BuildContext context, StateSetter setState) {
      return Padding(
        padding: EdgeInsets.only(
            top: SizeConfig.blockSizeHorizontal * 10,
            left: SizeConfig.blockSizeVertical * 2.5,
            right: SizeConfig.blockSizeVertical * 2.5,
            bottom: SizeConfig.screenHeight / 8),
        child: SizedBox(
          width: SizeConfig.blockSizeHorizontal * 100,
          height: SizeConfig.blockSizeVertical * 40,
          child: Container(
            decoration: BoxDecoration(
                color: Colors.grey[400],
                borderRadius: BorderRadius.circular(30),
                border: Border.all(
                    color: Colors.black45, style: BorderStyle.solid, width: 4)),
            child: Padding(
              padding: EdgeInsets.all(8.0),
              child: ToDoColumn(setState, checked),
            ),
          ),
        ),
      );
    });
  }

  
  Column ToDoColumn(
      StateSetter setState, bool checked) {
        
    return Column(children: [
      for (final value in widget.list)
        CheckboxListTile(
          value: checked,
          onChanged: (_value_1) {
            setState(() {
              checked = _value_1!;
            });
          },
          title: Text('${value}'),
          activeColor: Colors.green,
          checkColor: Colors.black,
        )
    ]);
  }
}

landing_page.dart

import 'package:flutter/material.dart';
import 'package:flutter_application_1/presentation/widgets/to_do_section.dart';

 final _textController = TextEditingController();
    String userInput = "";
class LandingPage extends StatefulWidget {
  const LandingPage({Key? key}) : super(key: key);

  @override
  State<LandingPage> createState() => _LandingPageState();
}

class _LandingPageState extends State<LandingPage> {
  
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Center(child: Text("To-Do-App")),
        backgroundColor: Colors.redAccent,
      ),
      body: SingleChildScrollView(
        child: Column(
          children: [ToDos(list: toDoList), ToDoAdd()],
        ),
      ),
    );
  }

 

  Column ToDoAdd() {
    return Column(
          children:  [
            Padding(
              padding: EdgeInsets.only(top: 8.0, left: 20, right: 20, bottom: 20),
              child: TextField(
                onChanged: (value) => setState(() => userInput = value) ,
                
                textAlign: TextAlign.center,
                decoration: InputDecoration(
                  border: OutlineInputBorder(),
                  hintText: "Add a new ToDo",
                )  ,
              ),
              
            ),
            MaterialButton(
              color: Colors.redAccent,
                onPressed: () {
                  setState(() {
                  toDoList.add(userInput);
                  
                });
                  
                },
                child: Text("Admit", style: TextStyle(color: Colors.white),),
                ),
                Text(userInput)
          ],
        );
  }


}

You initialize `bool checked= false;` on `build`, so everytime you check it and call `setState` then the `checked` value will be initialized to false. — Miftakhul Arzak, Jul 15 '22 at 08:07

score 2 · Accepted Answer · answered Jul 15 '22 at 10:21

Every variable declared inside the build method will be redeclared on each build. You could move its declaration outside and assign a value in the initState method.

Also, the use of the StatefulBuilder is not justified in your code. You could simply use the StatefulWidget as it is.

I will take the model class from @yeasin-sheikh

class Task {
  final String text;
  final bool isChecked;

  Task({
    required this.text,
    this.isChecked = false,
  });

  Task copyWith({
    String? text,
    bool? isChecked,
  }) {
    return Task(
      text: text ?? this.text,
      isChecked: isChecked ?? this.isChecked,
    );
  }
}

This example is a reduced one that accomplish what you are trying to do. Please notice that I'm not reproducing your design. The function addRandomToDo() could be replaced with your code for adding Tasks to the app.

class ToDoPage extends StatefulWidget {
  const ToDoPage({Key? key}) : super(key: key);

  @override
  State<ToDoPage> createState() => _ToDoPageState();
}

class _ToDoPageState extends State<ToDoPage> {
  final tasks = <Task>[];

  void addRandomToDo() {
    setState(() {
      tasks.add(Task(text: 'Random ToDo ${tasks.length + 1}'));
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('ToDo App'),
      ),
      body: ListView.builder(
          itemCount: tasks.length,
          itemBuilder: (context, index) {
            return CheckboxListTile(
              key: ObjectKey(tasks[index]),
              title: Text(tasks[index].text),
              value: tasks[index].isChecked,
              onChanged: (isChecked) {
                setState(() {
                  tasks[index] = tasks[index].copyWith(isChecked: isChecked);
                });
              },
            );
          }),
      floatingActionButton: FloatingActionButton(
        onPressed: addRandomToDo,
        tooltip: 'Add ToDo',
        child: const Icon(Icons.add),
      ),
    );
  }
}

Tips:

The use of Column for this example is not recommended. The best is to use a ListView.builder() and the reason is that when you use a Column and you have more element than the screen can render the app will also render the ones that are offscreen and will result in a lack of performance but the use of ListView will be best because it only renders a few elements offscreen (maybe two or three) to avoid a memory overload and it will load and render the elements as you scroll.
Is a best practice to not use functions to return a piece of the screen but to split it into widgets. (Instead of having a ToDoColumn function just change it for a ToDoColumnWidget). The explanation for this is that will incurre in a lack of performance because all functions will be re-rendered on every widget build.
This piece of code :

EdgeInsets.only(top: 8.0, left: 20, right: 20, bottom: 20)
Could be changed for this one:

EdgeInsets.fromLTRB(20, 8, 20, 20)

score 1 · Answer 2 · answered Jul 15 '22 at 08:10

1

You have defined isSelected inside the build method. The build method is invoked each time you set the state. Please move it to initState.

  bool checked= false;

Define bool checked = false outside the build method or in initstate

answered Jul 15 '22 at 08:10

Kaushik Chandru

15,510
2
12
30

score 1 · Answer 3 · answered Jul 15 '22 at 08:32

Putting variables inside build method will reset the bool and always be false. Also on your snippet you are just holding text without check state. On evey-build it will also reset on this point.

You can remove StatefulBuilder while this is already a StatefulWidget. Try using state-management like riverpod or bloc instead of using global variables in project cases.

As for the solution, I am creating a model class.

class Task {
  final String text;
  final bool isChecked;

  Task({
    required this.text,
    this.isChecked = false,
  });

  Task copyWith({
    String? text,
    bool? isChecked,
  }) {
    return Task(
      text: text ?? this.text,
      isChecked: isChecked ?? this.isChecked,
    );
  }
}

Now the list will be var toDoList = [Task(text: "")];

And your ToDos

class ToDos extends StatefulWidget {
  final List<Task> list;
  const ToDos({
    Key? key,
    required this.list,
  }) : super(key: key);

  @override
  State<ToDos> createState() => _ToDosState();
}

class _ToDosState extends State<ToDos> {
  @override
  Widget build(BuildContext context) {
    //todo: remove  [StatefulBuilder]
    return StatefulBuilder(builder: (BuildContext context, setStateSB) {
      return Container(
        child: Padding(
          padding: EdgeInsets.all(8.0),
          child: ToDoColumn(setStateSB),
        ),
      );
    });
  }

  //current
  Column ToDoColumn(
    StateSetter setStateSB,
  ) {
    return Column(children: [
      for (int i = 0; i < widget.list.length; i++)
        CheckboxListTile(
          value: widget.list[i].isChecked,
          onChanged: (_value_1) {
            widget.list[i] = widget.list[i].copyWith(isChecked: _value_1);

            setState(() {});
            setStateSB(() {});
          },
          title: Text('${widget.list[i].isChecked}'),
          activeColor: Colors.green,
          checkColor: Colors.black,
        )
    ]);
  }
}

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flutter dynamic Checkboxes don't check

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