How to automatically select all items above the selected one flutter

Note, this example isn’t perfect, but it’s a working example that can get you thinking, as I don’t know the bigger picture

Here’s my approach:

1. get the widget and index of the currently selected value using .indexOf()

2. loop over all the widgets until the previously gotten index

for (var i = 0; i < _data.indexOf(item); i++) {
                    _data[i].isChecked = value!;
                  }

Code example

create a class called CheckBoxModel:

class CheckBoxModel {
  bool isChecked = false;
  String text = "";
  CheckBoxModel({required this.isChecked, required this.text});
}

and then, generated 30 widgets:

final _data = List.generate(
    30, (index) => CheckBoxModel(isChecked: false, text: "Item $index"));

and used it correspondingly:

Column(
        children: [
          for (var item in _data)
            CheckboxListTile(
              value: item.isChecked,
              onChanged: (value) {
                setState(() {
                  for (var i = 0; i < _data.indexOf(item); i++) {
                    _data[i].isChecked = value!;
                  }
                });
              },
              title: Text(item.text),
            ),
        ],
      )

Here’s a complete runnable snipppet:

import 'package:flutter/material.dart';

const Color darkBlue = Color.fromARGB(255, 18, 32, 47);

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

class CheckBoxModel {
  bool isChecked = false;
  String text = "";
  CheckBoxModel({required this.isChecked, required this.text});
}

final _data = List.generate(
    30, (index) => CheckBoxModel(isChecked: false, text: "Item $index"));

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData.dark().copyWith(
        scaffoldBackgroundColor: darkBlue,
      ),
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        body: Center(
          child: Testing(),
        ),
      ),
    );
  }
}

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

  @override
  State<Testing> createState() => _TestingState();
}

class _TestingState extends State<Testing> {
  @override
  Widget build(BuildContext context) {
    return SingleChildScrollView(
      child: Column(
        children: [
          for (var item in _data)
            CheckboxListTile(
              value: item.isChecked,
              onChanged: (value) {
                setState(() {
                  for (var i = 0; i < _data.indexOf(item); i++) {
                    _data[i].isChecked = value!;
                  }
                });
              },
              title: Text(item.text),
            ),
        ],
      ),
    );
  }
}