轻按但使用我的脚手架主体时如何导航BottomNavigationBar项？

Question

enter image description here

DefaultTabController(
      length: 3,
      initialIndex: 1,
      child: Scaffold(
        bottomNavigationBar: BottomNavigationBar(
          type: BottomNavigationBarType.fixed,
          backgroundColor: Colors.grey[900],
          items: const <BottomNavigationBarItem>[
            BottomNavigationBarItem(
              icon: Icon(Icons.offline_bolt),
              title: Text('Shorts'),
            ),
            BottomNavigationBarItem(
              icon: Icon(Icons.graphic_eq),
              title: Text('Activity'),
            ),
            BottomNavigationBarItem(
              icon: Icon(Icons.cloud_upload),
              title: Text('Upload'),
            ),
            BottomNavigationBarItem(
              icon: Icon(Icons.email),
              title: Text('Messages'),
            ),
            BottomNavigationBarItem(
              icon: Icon(Icons.menu),
              title: Text('More'),
            ),
          ],
          currentIndex: _selectedIndex,
          selectedItemColor: Colors.white,
          unselectedItemColor: Colors.grey,
          onTap: _onItemTapped,
        ),
        body: NestedScrollView(
          controller: _scrollViewController,
          headerSliverBuilder: (BuildContext context, bool boxIsScrolled) {
            return <Widget>[
              SliverAppBar(
                centerTitle: true,
                leading: IconButton(
                  onPressed: () {
                    Navigator.push(
                        context,
                        MaterialPageRoute(
                            builder: (context) => HeadingCircle()));
                  },
                  icon: Icon(Icons.account_circle),
                ),
                actions: [
                  IconButton(
                    color: Colors.grey,
                    icon: Icon(Icons.search),
                    onPressed: () {},
                  ),
                ],
                backgroundColor: Colors.grey[900],
                title: Text(
                  'dribbble',
                  style: TextStyle(fontFamily: 'Pacifico'),
                ),
                pinned: true,
                floating: true,
                forceElevated: boxIsScrolled,
                bottom: TabBar(
                  tabs: <Widget>[
                    Tab(
                      text: "Following",
                    ),
                    Tab(
                      text: "Popular",
                    ),
                    Tab(
                      text: "Recent",
                    )
                  ],
                  controller: _tabController,
                ),
              ),
            ];
          },
          body: TabBarView(
            children: <Widget>[
              Tab(
                child: Text('1'),
              ),
              Tab(
                child: Text('2'),
              ),
              Tab(
                child: Text('3'),
              ),
            ],
            controller: _tabController,
          ),
        ),
      ),
    );