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.

// Template: dev/snippets/config/templates/stateful_widget_scaffold_center.tmpl
//
// Comment lines marked with "▼▼▼" and "▲▲▲" are used for authoring
// of samples, and may be ignored if you are just exploring the sample.

// Flutter code sample for Offstage
//
//***************************************************************************
//* ▼▼▼▼▼▼▼▼ description ▼▼▼▼▼▼▼▼ (do not modify or remove section marker)

// This example shows a [FlutterLogo] widget when the `_offstage` member field
// is false, and hides it without any room in the parent when it is true. When
// offstage, this app displays a button to get the logo size, which will be
// displayed in a [SnackBar].

//* ▲▲▲▲▲▲▲▲ description ▲▲▲▲▲▲▲▲ (do not modify or remove section marker)
//***************************************************************************

import 'package:flutter/material.dart';

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

/// This is the main application widget.
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(),
        ),
      ),
    );
  }
}

/// This is the stateful widget that the main application instantiates.
class MyStatefulWidget extends StatefulWidget {
  const MyStatefulWidget({Key? key}) : super(key: key);

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

/// This is the private State class that goes with MyStatefulWidget.
class _MyStatefulWidgetState extends State<MyStatefulWidget> {
//********************************************************************
//* ▼▼▼▼▼▼▼▼ code ▼▼▼▼▼▼▼▼ (do not modify or remove section marker)

  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()}'),
                  ),
                );
              }),
      ],
    );
  }

//* ▲▲▲▲▲▲▲▲ code ▲▲▲▲▲▲▲▲ (do not modify or remove section marker)
//********************************************************************

}