嵌套 TabBar 导航中的永久 AppBar

如何解决嵌套 TabBar 导航中的永久 AppBar

我是 Flutter 的新手，我面临这样一个问题：

1. 我有一个主文件来运行我的 web flutter 应用程序
2. 我的主页文件包含
3. 一个带有四个选项卡的 TabBar 的 AppBar
4. 每个标签都有两个弹出菜单项
5. 现在的问题是，当我点击一个菜单项时，它会将我带到其内容“DemoData”，但 AppBar 消失了，这不是我想要的
6. 所以现在我想知道如果可能的话如何实现这种行为。

这是我的代码：

    import 'package:flutter/material.dart';
    import 'package:nested_navigation_demo/home_page.dart';
    
    void main() {
      runApp(MyApp());
    }
    
    //homePage
    
    class MyApp extends StatelessWidget {
    
      @override
      Widget build(BuildContext context) {
        return MaterialApp(
          home: DefaultTabController(
            length: 4,child: Scaffold(
              appBar: AppBar(
                title: Text(
                  'Nested Tab Navigation Demo'
                ),bottom: TabBar(
                  tabs: [
                    Tab(
                      text: 'Explore',),Tab(
                      text: 'Discover',Tab(
                      text: 'Use',Tab(
                      text: 'Demo',)
                  ],body: TabBarView(
                  children: [
                    Center(
                      child: Container(
                          color:Colors.blue,child: DemoPage(),Container(
                        color:Colors.red,child:
                       DemoPage(),Container(
                        color:Colors.green,Container(
                        color:Colors.yellow,],)
            ),);
      }
    }
    
    //Demo page
    class DemoPage extends StatelessWidget {
      @override
      Widget build(BuildContext context) {
        // SignUpPage builds its own Navigator which ends up being a nested
        // Navigator in our app.
        return Navigator(
          initialRoute: 'DemoData',onGenerateRoute: (RouteSettings settings) {
            WidgetBuilder builder;
            switch (settings.name) {
              case 'DemoData':
              // Assume CollectPersonalInfoPage collects personal info and then
              // navigates to 'signup/choose_credentials'.
                builder = (BuildContext _) => HorizontalMenu();
                break;
    
              default:
                throw Exception('Invalid route: ${settings.name}');
            }
            return MaterialPageRoute(builder: builder,settings: settings);
          },);
      }
    }
    
    //horizontalMenu
    class HorizontalMenu extends StatefulWidget {
      //const HorizontalMenu({Key key}) : super(key: key);
    
      @override
      _HorizontalMenuState createState() => _HorizontalMenuState();
    }
    
    class _HorizontalMenuState extends State<HorizontalMenu> {
      @override
      Widget build(BuildContext context) {
        return Container(
        child:  Column(
          mainAxisAlignment: MainAxisAlignment.center,children: [
            Row(
              mainAxisAlignment: MainAxisAlignment.center,children: [
                Padding(
                  padding: const EdgeInsets.all(8.0),child: About(),Padding(
                  padding: const EdgeInsets.all(8.0),child: Stakeholders(),)
          ],);
      }
    }
    
    //About
    class About extends StatefulWidget {
      //const About({Key key}) : super(key: key);
    
      @override
      _AboutState createState() => _AboutState();
    }
    
    class _AboutState extends State<About> with
        AutomaticKeepAliveClientMixin<About> {
      @override
      bool get wantKeepAlive => true;
    
      @override
      void initState() {
        super.initState();
      }
      @override
      Widget build(BuildContext context) {
        return PopupMenuButton<int>(
          itemBuilder: (context) => [
            PopupMenuItem(
              value: 1,child: Column(
                children: [
                  ListTile(
                    //horizontalTitleGap:5.0,title: InkWell(
                      child: Text(
                        'Demo data1',style: TextStyle(
                            color: Colors.white
                        ),onTap: (){
                        Navigator.of(context).pushReplacement(
                            MaterialPageRoute(
                              builder: (context) => DemoData(),)
                        );
                      },ListTile(
                    title:InkWell(
                      child: Text(
                        'Demo data2',ListTile(
                    title: InkWell(
                      child: Text(
                        'Demo data3',onTap: (){
                        Navigator.of(context).pushReplacement(
                          MaterialPageRoute(
                            builder: (context) => DemoData(),);
                        //Navigator.push(context,DemoData());
                      },icon: Icon(Icons.apps,color: Colors.white,size: 30.0,offset: Offset(0.0,100.0),color: Colors.black,tooltip: 'About',);
      }
    }
    
    //Stakeholders
    class Stakeholders extends StatefulWidget {
      @override
      _StakeholdersState createState() => _StakeholdersState();
    }
    
    class _StakeholdersState extends State<Stakeholders> {
      @override
      Widget build(BuildContext context) {
        return PopupMenuButton<int>(
          itemBuilder: (context) => [
            PopupMenuItem(
              value: 1,);
      }
    }
    
    //DemoData
    class DemoData extends StatefulWidget {
      //const DemoData({Key key}) : super(key: key);
    
      @override
      _DemoDataState createState() => _DemoDataState();
    }
    
    class _DemoDataState extends State<DemoData> {
      @override
      Widget build(BuildContext context) {
        return Scaffold(
          appBar: AppBar(
            title: Text(
              'First demo page',body: Container(
            color: Colors.purple,child: Center(
              child: TextButton(
                onPressed: () {
                  Navigator.of(context).pushReplacement(
                    MaterialPageRoute(
                      builder: (context) => SecondDemoData(),);
                },child: Text(
                  'Take me to another page'
                ),);
      }
    }
    
    //SecondDemoData
    class SecondDemoData extends StatefulWidget {
      //const DemoData({Key key}) : super(key: key);
    
      @override
      _SecondDemoDataState createState() => _SecondDemoDataState();
    }
    
    class _SecondDemoDataState extends State<SecondDemoData> {
      @override
      Widget build(BuildContext context) {
        return Scaffold(
          appBar: AppBar(
            title: Text(
            'Second page demo',)
          ),body: Container(
            color: Colors.yellow,child: Center(
              child: TextButton(
                onPressed: () {
    
                  Navigator.of(context).pushReplacement(
                      MaterialPageRoute(
                        builder: (context) =>  DemoData(),)
                  );
                },child: Text(
                    'Take me to another page'
                ),);
      }
    }