SliverAppBar无法滚动

Question

SliverAppBar无法滚动

SliverAppBar和SliverList无法滚动，只能在根脚手架内正常工作，否则不能滚动任何东西

问题代码

return CupertinoApp(
    localizationsDelegates: const <LocalizationsDelegate<dynamic>>[
      DefaultMaterialLocalizations.delegate,
      DefaultWidgetsLocalizations.delegate,
    ],
    title: 'Flutter Demo',
    theme: CupertinoThemeData(
      primaryColor: Colors.blue,
    ),
    home: Scaffold(
        body: Center(
            child: Stack(
          children: [
            CustomScrollView(
              controller: ScrollController(initialScrollOffset: 0),
              physics: BouncingScrollPhysics(),
              shrinkWrap: true,
              slivers: <Widget>[
                SliverAppBar(
                  floating: true,
                  pinned: false,
                  snap: false,
                  flexibleSpace: FlexibleSpaceBar(
                    background: Image.asset("assets/images/wxbg.png"),
                  ),
                  expandedHeight: 156,
                ),
                SliverList(
                    delegate: SliverChildBuilderDelegate(
                  (context, index) => ListTile(
                    title: Text(
                      "你们啊,naive",
                      style: TextStyle(fontSize: 20.0),
                    ),
                  ),
                  childCount: 20,
                ))
              ],
            ),
            PreferredSize(
                child: Container(
                  width: double.infinity,
                  height: double.infinity,
                  decoration: BoxDecoration(color: Colors.transparent),
                  child: SafeArea(
                      child: AppBar(
                    centerTitle: true,
                    elevation: 0,
                    backgroundColor: Colors.transparent,
                    title: Text("?"),
                    leading: IconButton(
                        icon: Icon(Icons.backspace), onPressed: () => {}),
                  )),
                ),
                preferredSize: Size(double.infinity, 50)),
          ],
        )),
        bottomNavigationBar: BottomNavigationBar(
          items: <BottomNavigationBarItem>[
            BottomNavigationBarItem(
              icon: SvgPicture.asset("assets/images/test.svg",
                  height: 30, width: 30),
              title: Text('Home'),
            ),
            BottomNavigationBarItem(
              icon: Icon(
                Icons.business,
                size: 30,
              ),
              title: Text('Business'),
            ),
            BottomNavigationBarItem(
              icon: Icon(
                Icons.school,
                size: 30,
              ),
              title: Text('School'),
            ),
          ],
          currentIndex: state.selectedIndex,
          selectedItemColor: Colors.amber[800],
        )),
    debugShowCheckedModeBanner: false,
  );

做得好

return CupertinoApp(
    localizationsDelegates: const <LocalizationsDelegate<dynamic>>[
      DefaultMaterialLocalizations.delegate,
      DefaultWidgetsLocalizations.delegate,
    ],
    title: 'Flutter Demo',
    theme: CupertinoThemeData(
      primaryColor: Colors.blue,
    ),
    home: Scaffold(
        body:CustomScrollView( //
          controller: ScrollController(initialScrollOffset: 0),
          physics: BouncingScrollPhysics(),
          shrinkWrap: true,
          slivers: <Widget>[
            SliverAppBar(
              floating: true,
              pinned: false,
              snap: false,
              flexibleSpace: FlexibleSpaceBar(
                background: Image.asset("assets/images/wxbg.png"),
              ),
              expandedHeight: 156,
            ),
            SliverList(
                delegate: SliverChildBuilderDelegate(
                      (context, index) => ListTile(
                    title: Text(
                      "你们啊,naive",
                      style: TextStyle(fontSize: 20.0),
                    ),
                  ),
                  childCount: 20,
                ))
          ],
        )),
    debugShowCheckedModeBanner: false,
  );

为什么必须在根层中使用SliverAppBar？我如何像android片段工具栏一样使用它，产生崩溃效果，我只学习了一周的颤振，有人可以帮助我吗？