checkbox lost checked value in flutter - flutter

Question

I show my list of answers via ListView.builder and check value on checkbox work ok, but when I scroll down and turn back checked value is lost. Other way when lost focus in checked answer automatic checkbox lost checked value.
Below is my code. I would be grateful if someone could help me.
class AnswerItem extends StatefulWidget {
#override
_AnswerItemState createState() => _AnswerItemState();
}
class _AnswerItemState extends State<AnswerItem> {
List<bool> _data = [false, false, false, false];
void _onChange(bool value, int index) {
setState(() {
_data[index] = value;
});
}
Widget build(BuildContext context) {
final questionItems = Provider.of<Item>(context);
List<Answer> listOfAnswers = questionItems.answers.toList();
return SingleChildScrollView(
child:
ListView.builder(
shrinkWrap: true,
itemCount: listOfAnswers.length,
itemBuilder: (context, index) {
return Padding(
padding: const EdgeInsets.symmetric(horizontal: 25),
child: Card(
child: Padding(
padding: const EdgeInsets.symmetric(horizontal: 10),
child: CheckboxListTile(
value: _data[index],
title: Text(listOfAnswers[index].title),
onChanged: (val) {
_onChange(val, index);
},
),
),
),
);
},
),
);
}
}

Answer 1

Somewhere, you're confusing "model" with "view", and storing state in the view. This necessarily means when the view is refreshed or updated, you will lose state.
Specifically, your model here appears to be listOfAnswers, which being a local variable inside a build() method, will possibly be rebuilt on every refresh (possibly 120 fps!). You need to put your model outside any build method.