如何在flutter中将小部件定位到导航栏的底部？

BottomNavigationBar(
  currentIndex: _selectedIndex,
  onTap: _onItemTapped,
  items: const <BottomNavigationBarItem>[
    BottomNavigationBarItem(
      icon: Icon(Icons.home),
      label: 'Home',
    ),
    BottomNavigationBarItem(
      icon: Icon(Icons.business),
      label: 'Business',
    ),
    BottomNavigationBarItem(
      icon: Icon(Icons.school),
      label: 'School',
    ),
  ],
)

IndexedStack(
  index: _selectedIndex,
  children: <Widget>[
    HomeWidget(),
    BusinessWidget(),
    SchoolWidget(),
  ],
)

int _selectedIndex = 0;

void _onItemTapped(int index) {
  setState(() {
    _selectedIndex = index;
  });
}