I imported search bar in flutter, and I got some error messages

Question

Code: /// Flutter code sample for BottomNavigationBar

// This example shows a [BottomNavigationBar] as it is used within a [Scaffold]
// widget. The [BottomNavigationBar] has three [BottomNavigationBarItem]
// widgets, which means it defaults to [BottomNavigationBarType.fixed], and
// the [currentIndex] is set to index 0. The selected item is
// amber. The `_onItemTapped` function changes the selected item's index
// and displays a corresponding message in the center of the [Scaffold].

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:flutter_search_bar/flutter_search_bar.dart';
import 'package:flutter_login/flutter_login.dart';

const users = const {
  '[email protected]': '12345',
  '[email protected]': 'hunter',
};

class LoginScreen extends StatelessWidget {
  Duration get loginTime => Duration(milliseconds: 2250);

  Future<String> _authUser(LoginData data) {
    print('Name: ${data.name}, Password: ${data.password}');
    return Future.delayed(loginTime).then((_) {
      if (!users.containsKey(data.name)) {
        return 'User not exists';
      }
      if (users[data.name] != data.password) {
        return 'Password does not match';
     }
      return null;
    });
  }

  Future<String> _recoverPassword(String name) {
    print('Name: $name');
    return Future.delayed(loginTime).then((_) {
      if (!users.containsKey(name)) {
        return 'User not exists';
      }
      return null;
    });
  }

  @override
  Widget build(BuildContext context) {
    return FlutterLogin(
      title: 'ECORP',
      logo: 'assets/images/ecorp-lightblue.png',
      onLogin: _authUser,
      onSignup: _authUser,
      onSubmitAnimationCompleted: () {
        Navigator.of(context).pushReplacement(MaterialPageRoute(
          builder: (context) => DashboardScreen(),
        ));
      },
      onRecoverPassword: _recoverPassword,
    );
  }
}
class _MyHomePageState extends State<MyHomePage> {
  SearchBar searchBar;

  AppBar buildAppBar(BuildContext context) {
    return new AppBar(
        title: new Text('My Home Page'),
        actions: [searchBar.getSearchAction(context)]
    );
 }

  _MyHomePageState() {
    searchBar = new SearchBar(
        inBar: false,
        setState: setState,
        onSubmitted: print,
        buildDefaultAppBar: buildAppBar
    );
  }

 @override
  Widget build(BuildContext context) {
    return new Scaffold(
        appBar: searchBar.build(context)
    );
  }
}


void main() => runApp(const MyApp()); // This is the main application widget.

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  static const String _title = 'Flutter Code Sample';

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      title: _title,
      home: MyStatefulWidget(),
    );
  }
}

/// This is the stateful widget that the main application instantiates.
class MyStatefulWidget extends StatefulWidget {
  const MyStatefulWidget({Key? key}) : super(key: key);

  @override
  State<MyStatefulWidget> createState() => _MyStatefulWidgetState();
}


/// This is the private State class that goes with MyStatefulWidget.
class _MyStatefulWidgetState extends State<MyStatefulWidget> {
  int _selectedIndex = 0;

  static const List<Widget> _widgetOptions = <Widget>[
    Text(
      'Reuse',
      style: TextStyle(fontSize: 20),
    ),
        Text(
          "Reduce",
          style: TextStyle(fontSize: 20),
        ),

    Text(
      'Recycle',
     style: TextStyle(fontSize: 20),
    )
  ];

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Food3Rs'),
        backgroundColor: Colors.green,
      ),
      drawer: Drawer(
        child: ListView(padding: EdgeInsets.zero, children: const <Widget>[
          DrawerHeader(
            decoration: BoxDecoration(color: Colors.green),
            child: Text(
              'Food Reduction',
              style: TextStyle(
                color: Colors.white,
                fontSize: 24,
              ),
            ),
          ),
          ListTile(
            leading: Icon(Icons.bookmark),
            title: Text('Saved Recipes'),
          ),
          ListTile(
            leading: Icon(Icons.account_circle),
            title: Text('Profile'),
          ),
          ListTile(leading: Icon(Icons.settings), title: Text('Settings'))
        ]),
      ),
     body: Center(
        child: _widgetOptions.elementAt(_selectedIndex),
      ),
      bottomNavigationBar: BottomNavigationBar(
        items: const <BottomNavigationBarItem>[
          BottomNavigationBarItem(
            icon: Icon(Icons.food_bank_outlined),
            label: ('Reduce'),
            backgroundColor: (Colors.lightGreen),
          ),
          BottomNavigationBarItem(
            icon: Icon(Icons.food_bank),
            label: ('Reuse'),
          ),
          BottomNavigationBarItem(
            icon: Icon(Icons.cloud),
            label: ('Recycle'),
            backgroundColor: (Colors.lightGreen),
          )
        ],
        currentIndex: _selectedIndex,
        selectedItemColor: Colors.amber[800],
        onTap: _onItemTapped,
      ),
    );
  }
}

Error messages: The return type 'Null' isn't a 'FutureOr', as required by the closure's context. The return type 'Null' isn't a 'FutureOr', as required by the closure's context. The method 'DashboardScreen' isn't defined for the type 'LoginScreen'. 'dynamic' doesn't conform to the bound 'StatefulWidget' of the type parameter 'T'. The name 'MyHomePage' isn't a type so it can't be used as a type argument. Non-nullable instance field 'searchBar' must be initialized. The declaration '_MyHomePageState' isn't referenced. The library 'package:flutter_search_bar/flutter_search_bar.dart' is legacy, and should not be imported into a null safe library. Typo: In word 'ECORP' Typo: In word 'ecorp' Typo: In word 'lightblue'