在flutter中获取Firebase数据作为Listview构建器

import 'package:flutter/material.dart';
import 'package:firebase_core/firebase_core.dart';
import 'package:cloud_firestore/cloud_firestore.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Firebase ListView Example',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatelessWidget {
  final CollectionReference usersRef =
      FirebaseFirestore.instance.collection('users');

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Firebase ListView Example'),
      ),
      body: StreamBuilder<QuerySnapshot>(
        stream: usersRef.snapshots(),
        builder: (BuildContext context, AsyncSnapshot<QuerySnapshot> snapshot) {
          if (snapshot.hasError) {
            return Text('Error: ${snapshot.error}');
          }

          if (snapshot.connectionState == ConnectionState.waiting) {
            return CircularProgressIndicator();
          }

          List<DocumentSnapshot> documents = snapshot.data.docs;
          List<String> usernames =
              documents.map((doc) => doc.data()['username']).toList();

          return ListView.builder(
            itemCount: usernames.length,
            itemBuilder: (BuildContext context, int index) {
              return ListTile(
                title: Text(usernames[index]),
              );
            },
          );
        },
      ),
    );
  }
}