examples/api/lib/widgets/basic/offstage.0.dart

// Copyright 2014 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// Flutter code sample for Offstage

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  static const String _title = 'Flutter Code Sample';

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: _title,
      home: Scaffold(
        appBar: AppBar(title: const Text(_title)),
        body: const Center(
          child: MyStatefulWidget(),
        ),
      ),
    );
  }
}

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

  @override
  State<MyStatefulWidget> createState() => _MyStatefulWidgetState();
}

class _MyStatefulWidgetState extends State<MyStatefulWidget> {
  final GlobalKey _key = GlobalKey();
  bool _offstage = true;

  Size _getFlutterLogoSize() {
    final RenderBox renderLogo =
        _key.currentContext!.findRenderObject()! as RenderBox;
    return renderLogo.size;
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: <Widget>[
        Offstage(
          offstage: _offstage,
          child: FlutterLogo(
            key: _key,
            size: 150.0,
          ),
        ),
        Text('Flutter logo is offstage: $_offstage'),
        ElevatedButton(
          child: const Text('Toggle Offstage Value'),
          onPressed: () {
            setState(() {
              _offstage = !_offstage;
            });
          },
        ),
        if (_offstage)
          ElevatedButton(
              child: const Text('Get Flutter Logo size'),
              onPressed: () {
                ScaffoldMessenger.of(context).showSnackBar(
                  SnackBar(
                    content:
                        Text('Flutter Logo size is ${_getFlutterLogoSize()}'),
                  ),
                );
              }),
      ],
    );
  }
}