FirebaseのデータベースからローカルPCにデータを保存する

import 'package:flutter/material.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:firebase_core/firebase_core.dart';
import 'firebase_options.dart';
import 'home.dart';

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp(
    options: DefaultFirebaseOptions.currentPlatform,
  );
  runApp(const MyApp());
}

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

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const LoginPage(title: 'Flutter Demo Home Page'),
    );
  }
}

class LoginPage extends StatefulWidget {
  const LoginPage({Key? key, required this.title}) : super(key: key);
  final String title;

  @override
  State<LoginPage> createState() => LoginPageState();
}

class LoginPageState extends State<LoginPage> {
  // Googleアカウントの表示名
  String infoText = '';

  // 公式ページのコードをそのままコピー
  Future<UserCredential> signInWithGooglePopup() async {
    // Create a new provider
    GoogleAuthProvider googleProvider = GoogleAuthProvider();
    googleProvider
        .addScope('https://www.googleapis.com/auth/contacts.readonly');
    googleProvider.setCustomParameters({'login_hint': 'user@example.com'});
    return await FirebaseAuth.instance.signInWithPopup(googleProvider);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        body: Center(
      child: Column(mainAxisAlignment: MainAxisAlignment.center, children: [
        TextButton(
          onPressed: () async {
            try {
              await signInWithGooglePopup();
              final User? user = FirebaseAuth.instance.currentUser;
              if (user != null) {
                await Navigator.of(context).pushReplacement(
                  MaterialPageRoute(builder: (context) {
                    return HomePage(user);
                  }),
                );
              }
            } catch (e) {
              setState(() {
                infoText = 'Loginに失敗しました:${e.toString()}';
              });
            }
          },
          child: const Text(
            'login',
            style: TextStyle(fontSize: 50),
          ),
        ),
        Text(infoText), // loginされなかった時のメッセージを表示
      ]),
    ));
  }
}

import 'package:firebase_auth/firebase_auth.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:flutter/material.dart';
import 'main.dart';

class HomePage extends StatelessWidget {
  HomePage(this.user);
  final User user;

  final TextEditingController _messageController = TextEditingController();

  void _sendMessage() {
    final String message = _messageController.text;
    final String userId = user.uid;
    final DateTime now = DateTime.now();

    final CollectionReference messages =
        FirebaseFirestore.instance.collection('messages');

    messages.add({
      'message': message,
      'userId': userId,
      'timestamp': now,
    });

    _messageController.clear();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('HOME'),
        actions: <Widget>[
          IconButton(
            icon: const Icon(Icons.logout),
            onPressed: () async {
              await FirebaseAuth.instance.signOut();
              await Navigator.of(context).pushReplacement(
                MaterialPageRoute(builder: (context) {
                  return LoginPage(title: 'Login Page');
                }),
              );
            },
          ),
        ],
      ),
      body: Padding(
        padding: const EdgeInsets.all(16.0),
        child: Column(
          children: [
            Expanded(
              child: StreamBuilder<QuerySnapshot>(
                stream: FirebaseFirestore.instance
                    .collection('messages')
                    .where('userId', isEqualTo: user.uid) // userIdが本人と同じもののみを取得
                    .snapshots(),
                builder: (context, snapshot) {
                  if (snapshot.hasData) {
                    final messages = snapshot.data!.docs;
                    return ListView.builder(
                      itemCount: messages.length,
                      itemBuilder: (context, index) {
                        final message = messages[index];
                        final String messageText = message['message'];
                        final String userId = message['userId'];
                        final Timestamp timestamp = message['timestamp'];
                        final DateTime dateTime = timestamp.toDate();

                        return ListTile(
                          title: Text(messageText),
                          subtitle:
                              Text('User ID: $userId\nTimestamp: $dateTime'),
                        );
                      },
                    );
                  } else {
                    return Center(child: CircularProgressIndicator());
                  }
                },
              ),
            ),
            SizedBox(height: 16.0),
            TextField(
              controller: _messageController,
              decoration: InputDecoration(
                hintText: 'メッセージを入力してください',
              ),
            ),
            SizedBox(height: 8.0),
            ElevatedButton(
              onPressed: _sendMessage,
              child: Text('送信'),
            ),
          ],
        ),
      ),
    );
  }
}