Flutter 如何从底部导航栏打开 bottomModal 表

在我的底部导航栏中，我有五个图标，其中四个图标打开4个不同的屏幕，我想要另一个图标打开showModalBottomSheet个，但当我实现它并运行应用程序时，它显示错误消息

在生成过程中调用setState()或markNeedsBuild().和‘Package:Ffltter/src/Widget/Navigator.dart’:失败的断言:行 2903位置18:‘！Navigator._DebugLocked’:不为真.

我也试过使用WidgetsBinding.instance？.addPostFrameCallback((_)，但它也显示错误提示为'This expression has a type of 'void' so its value can't be used.' 我该怎么办？?

class BottomNavigationPage extends StatefulWidget {
  const BottomNavigationPage({Key? key}) : super(key: key);

  @override
  State<BottomNavigationPage> createState() => _BottomNavigationPageState();
}

class _BottomNavigationPageState extends State<BottomNavigationPage> {
  int currentIndex = 1;

  @override
  Widget build(BuildContext context) {
    List body = [
      showModalBottomSheet(
          context: context,
          builder: (BuildContext context) {
            return const Containers(
              height: 400,
              color: Colors.green,
            );
          }),
      const Containers(
        height: 400,
        color: Colors.red,
      ),
      const Dashboard(),
      const DepartmentPage(),
      const Dashboard(),
      const DepartmentPage(),
    ];
    return Scaffold(
      body: Center(
        child: body[currentIndex],
      ),
      bottomNavigationBar: BottomNavigationBar(
        //showUnselectedLabels: true,
        selectedItemColor: AppColor.btnColor,
        selectedIconTheme: const IconThemeData(color: AppColor.btnColor),
        unselectedItemColor: Colors.black45,
        showSelectedLabels: true,
        currentIndex: currentIndex,
        onTap: (int newindex) {
          setState(() {
            currentIndex = newindex;
          });
        },
        items: const [
          BottomNavigationBarItem(
            label: '',
            activeIcon: Icon(
              Icons.menu,
              color: AppColor.btnColor,
              size: 30,
            ),
            icon: Icon(
              Icons.menu,
              size: 30,
            ),
          ),
          BottomNavigationBarItem(
            activeIcon: Icon(
              Icons.home,
              size: 30,
            ),
            label: 'होम',
            icon: Icon(
              Icons.home,
              size: 30,
            ),
          ),
          BottomNavigationBarItem(
            activeIcon: Icon(
              Icons.people,
              size: 30,
            ),
            label: 'शाखा हरु ',
            icon: Icon(
              Icons.people,
              size: 30,
            ),
          ),
          BottomNavigationBarItem(
            label: 'सूचना हरु',
            activeIcon: Icon(
              Icons.task,
              size: 30,
            ),
            icon: Icon(
              Icons.task,
              size: 30,
            ),
          ),
          BottomNavigationBarItem(
            activeIcon: Icon(
              Icons.task,
              size: 30,
            ),
            label: 'सूचना हरु',
            icon: Icon(
              Icons.task,
              size: 30,
            ),
          ),
        ],
      ),
    );
  }
}