如何在flutter中管理离线firebase数据库？

dependencies:
  flutter:
    sdk: flutter
  firebase_core: ^1.0.4
  cloud_firestore: ^2.2.2

import 'package:firebase_core/firebase_core.dart';

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

import 'package:cloud_firestore/cloud_firestore.dart';

FirebaseFirestore.instance.settings = Settings(persistenceEnabled: true);

import 'package:cloud_firestore/cloud_firestore.dart';

void main() async {
  // ...

  CollectionReference users = FirebaseFirestore.instance.collection('users');

  // 读取数据
  QuerySnapshot snapshot = await users.get();
  snapshot.docs.forEach((doc) {
    print(doc.data());
  });

  // 写入数据
  users.doc('user1').set({
    'name': 'John',
    'age': 25,
  });
}

import 'package:cloud_firestore/cloud_firestore.dart';

void main() async {
  // ...

  CollectionReference users = FirebaseFirestore.instance.collection('users');

  users.snapshots().listen((snapshot) {
    snapshot.docs.forEach((doc) {
      print(doc.data());
    });
  });
}