Stateless widget example

readme.md

Stateless widget example

Created with <3 with dartpad.dev.

main.dart

// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  final String title;

  const MyHomePage({
    Key? key,
    required this.title,
  }) : super(key: key);

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

class _MyHomePageState extends State<MyHomePage> {
  
  // This is state, which can change, 
  // and each time it does anything that depends on it changes
  bool _toggled = false;

  void _switchToggle(bool value) {
    setState(() {
      _toggled = value;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Text("Parent state: $_toggled"),
            MyToggle(_toggled, _switchToggle),
          ],
        ),
      ),
    );
  }
}

class MyToggle extends StatelessWidget {
  const MyToggle(this._toggled, this._switch);
  
  // This is set by the constructor above - it's never set by MyToggle directly
  // It's not state, a new MyToggle is created each time the parent re-renders
  final bool _toggled;
  final Function(bool) _switch;
  
  @override
  Widget build(BuildContext context) {
    return Switch(
      // This bool value toggles the switch.
      value: _toggled,
      activeColor: Colors.red,
      onChanged: (bool value) {
        // This is called when the user toggles the switch.
        _switch(value);
      },
    );
  }
}