作为子组件，不输出，不占空间，不参与点击测试

Offstage children are still active: they can receive focus and have keyboard input directed to them.

bool offstage属性决定显示与否。

import 'package:flutter/material.dart';/// Flutter code sample for [Offstage].void main() => runApp(const OffstageApp());class OffstageApp extends StatelessWidget {const OffstageApp({super.key});@overrideWidget build(BuildContext context) {return MaterialApp(home: Scaffold(appBar: AppBar(title: const Text('Offstage Sample')),body: const Center(child: OffstageExample(),),),);}
}class OffstageExample extends StatefulWidget {const OffstageExample({super.key});@overrideState<OffstageExample> createState() => _OffstageExampleState();
}class _OffstageExampleState extends State<OffstageExample> {final GlobalKey _key = GlobalKey();bool _offstage = true;Size _getFlutterLogoSize() {final RenderBox renderLogo =_key.currentContext!.findRenderObject()! as RenderBox;return renderLogo.size;}@overrideWidget 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()}'),),);}),],);}
}