Tick a Checkbox

Part of the Making It Interactive section of Coddy's Flutter journey. Lesson 28 of 34.

A Checkbox works like a Switch: a value: to draw, and an onChanged that you answer with setState.

Checkbox(
  value: _agreed,
  onChanged: (bool? value) {
    setState(() {
      _agreed = value ?? false;
    });
  },
)

One difference: its value is a bool?, a bool or null. A checkbox can have a third, empty state, which you will not use here. Since _agreed is a plain bool, turn a possible null into false with ??, as you did with int.tryParse.

A checkbox is often the thing that lets a button be pressed: tick "I agree" and Continue stops being grey.

Challenge

Easy

Make the checkbox tick and untick: store its value in _agreed.
Grey out Continue until the box is ticked.

Try it yourself

import 'package:flutter/material.dart';

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

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

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: const HomePage(),
    );
  }
}

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

  @override
  State<HomePage> createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  bool _agreed = false;

  void _continue() {
    ScaffoldMessenger.of(context).showSnackBar(
      const SnackBar(content: Text('Welcome!')),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Rules')),
      body: Center(
        child: Column(
          mainAxisSize: MainAxisSize.min,
          children: [
            Row(
              mainAxisSize: MainAxisSize.min,
              children: [
                Checkbox(
                  value: _agreed,
                  onChanged: (bool? value) {},
                ),
                const Text('I agree to the rules'),
              ],
            ),
            const SizedBox(height: 16),
            ElevatedButton(onPressed: _continue, child: const Text('Continue')),
          ],
        ),
      ),
    );
  }
}