如何在我的firebase和flutter应用程序上创建实时用户计数？

dependencies:
  firebase_core: ^1.0.0
  firebase_database: ^7.0.0

import 'package:firebase_core/firebase_core.dart';

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();
  runApp(MyApp());
}

import 'package:firebase_database/firebase_database.dart';

class UserCounterPage extends StatelessWidget {
  final DatabaseReference _userCountRef =
      FirebaseDatabase.instance.reference().child('userCount');

  @override
  Widget build(BuildContext context) {
    return StreamBuilder(
      stream: _userCountRef.onValue,
      builder: (context, snapshot) {
        if (snapshot.hasData && snapshot.data.snapshot.value != null) {
          int userCount = snapshot.data.snapshot.value;
          return Text('当前用户数：$userCount');
        } else {
          return Text('加载中...');
        }
      },
    );
  }
}

void updateUserCount(int count) {
  _userCountRef.set(count);
}