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Flutter Mobile Development · 课时

Firebase 配置与身份验证

在 Flutter 项目中配置 Firebase，并使用电子邮件/密码、Google 登录和其他提供商实现用户身份验证。

Firebase 配置与身份验证 是 CoddyKit 上的免费 Flutter Mobile Development 课时。 这是第 1 节课，共 4 节。 你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。 这是 Flutter Mobile Development 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 Flutter Mobile Development 课程共包含 4 节课。

本课时的部分内容尚未翻译，以英文显示。

Firebase for Flutter Apps

Welcome to Firebase integration! Firebase is a powerful platform by Google that offers many backend services for your mobile and web applications.

It acts as a Backend-as-a-Service (BaaS), meaning it handles server-side operations so you can focus on building your app's frontend.

In this lesson, we'll set up Firebase in a Flutter project and implement basic user authentication.

Firebase Project Setup

First, you need a Firebase project. Go to the Firebase Console and follow these steps:

  • Click 'Add project' and follow the prompts.
  • Once created, click the 'Add app' button (Android or iOS icon).
  • Register your app by providing the package name (Android) or bundle ID (iOS).
  • Download the configuration file: google-services.json for Android, GoogleService-Info.plist for iOS.

Adding Firebase to Flutter

After setting up your project in the Firebase Console, you need to add the necessary dependencies to your Flutter project's pubspec.yaml file.

We'll add firebase_core to initialize Firebase and firebase_auth for authentication.

Then, run flutter pub get in your terminal to fetch the packages.

Initialize Firebase Core

Before using any Firebase services, you must initialize Firebase in your Flutter app, usually in your main() function.

Make sure to call WidgetsFlutterBinding.ensureInitialized() before Firebase.initializeApp() to ensure Flutter's binding is initialized.

The FlutterFire CLI can generate firebase_options.dart for easy platform-specific setup.

import 'package:flutter/material.dart';
import 'package:firebase_core/firebase_core.dart';
// import 'firebase_options.dart'; // Generated by FlutterFire CLI

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Firebase App',
      home: Scaffold(
        appBar: AppBar(title: Text('Firebase Init')),
        body: Center(child: Text('Firebase initialized!')),
      ),
    );
  }
}

Config File Placement

Place the downloaded configuration files in their correct locations:

  • Android: Move google-services.json into the android/app/ directory of your Flutter project.
  • iOS: Open your Flutter project in Xcode (ios/Runner.xcworkspace), then drag GoogleService-Info.plist into the 'Runner' folder. Make sure to select 'Copy items if needed' and add to all targets.

Email/Password Sign Up

Firebase Authentication supports various sign-in methods. Let's start with Email and Password.

First, enable the 'Email/Password' provider in the Firebase Console under 'Authentication' -> 'Sign-in method'.

Then, use FirebaseAuth.instance.createUserWithEmailAndPassword to register new users.

import 'package:firebase_auth/firebase_auth.dart';

class AuthService {
  final FirebaseAuth _auth = FirebaseAuth.instance;

  Future<User?> signUp(String email, String password) async {
    try {
      UserCredential result = await _auth.createUserWithEmailAndPassword(
        email: email,
        password: password,
      );
      return result.user;
    } catch (e) {
      print(e.toString());
      return null;
    }
  }

  // This main is for demonstration of the function logic.
  // In a real app, Firebase.initializeApp() would be called once at app start.
  static void main() async {
    // Simulate Firebase being initialized
    // await Firebase.initializeApp(); 
    
    AuthService auth = AuthService();
    User? user = await auth.signUp("test@example.com", "password123");
    if (user != null) {
      print("Signed up user: ${user.email}");
    } else {
      print("Sign up failed.");
    }
  }
}

Email/Password Sign In

Once a user is registered, they can sign in using their email and password. This is done with the signInWithEmailAndPassword method.

Both sign-up and sign-in methods return a UserCredential object, which contains the User object if successful.

import 'package:firebase_auth/firebase_auth.dart';

class AuthService {
  final FirebaseAuth _auth = FirebaseAuth.instance;

  Future<User?> signIn(String email, String password) async {
    try {
      UserCredential result = await _auth.signInWithEmailAndPassword(
        email: email,
        password: password,
      );
      return result.user;
    } catch (e) {
      print(e.toString());
      return null;
    }
  }

  // This main is for demonstration of the function logic.
  // In a real app, Firebase.initializeApp() would be called once at app start.
  static void main() async {
    // Simulate Firebase being initialized
    // await Firebase.initializeApp(); 
    
    AuthService auth = AuthService();
    User? user = await auth.signIn("test@example.com", "password123");
    if (user != null) {
      print("Signed in user: ${user.email}");
    } else {
      print("Sign in failed.");
    }
  }
}

Monitoring Auth State

It's crucial to know if a user is currently signed in or out. Firebase Auth provides a stream called authStateChanges() that emits a new User object whenever the authentication state changes.

This stream can be used with a StreamBuilder widget to dynamically update your UI based on the user's login status.

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

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Auth State App',
      home: StreamBuilder<User?>(
        stream: FirebaseAuth.instance.authStateChanges(),
        builder: (context, snapshot) {
          if (snapshot.connectionState == ConnectionState.waiting) {
            return CircularProgressIndicator();
          }
          if (snapshot.hasData) {
            return HomeScreen(user: snapshot.data!); // User is signed in
          } else {
            return LoginScreen(); // User is signed out
          }
        },
      ),
    );
  }
}

class HomeScreen extends StatelessWidget {
  final User user;
  HomeScreen({required this.user});

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Welcome')),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Text('Logged in as: ${user.email}'),
            ElevatedButton(
              onPressed: () async {
                await FirebaseAuth.instance.signOut();
              },
              child: Text('Sign Out'),
            ),
          ],
        ),
      ),
    );
  }
}

Google Sign-In Setup

Google Sign-In is a popular and user-friendly authentication method. To enable it:

  • In Firebase Console, go to 'Authentication' -> 'Sign-in method' and enable 'Google'.
  • Add the google_sign_in package to your pubspec.yaml.
  • Android: Ensure your SHA-1 fingerprint is registered in Firebase project settings.
  • iOS: Add the Reverse Client ID to your Info.plist file (obtained from GoogleService-Info.plist).

Implementing Google Sign-In

After the setup, you can implement Google Sign-In using the GoogleSignIn package to get user credentials, and then sign in to Firebase with those credentials.

This involves using GoogleSignIn().signIn() and then creating a GoogleAuthProvider.credential to pass to FirebaseAuth.instance.signInWithCredential().

import 'package:firebase_auth/firebase_auth.dart';
import 'package:google_sign_in/google_sign_in.dart';

class GoogleAuthService {
  final FirebaseAuth _auth = FirebaseAuth.instance;
  final GoogleSignIn _googleSignIn = GoogleSignIn();

  Future<User?> signInWithGoogle() async {
    try {
      final GoogleSignInAccount? googleUser = await _googleSignIn.signIn();
      if (googleUser == null) return null; // User cancelled the sign-in

      final GoogleSignInAuthentication googleAuth = await googleUser.authentication;

      final AuthCredential credential = GoogleAuthProvider.credential(
        accessToken: googleAuth.accessToken,
        idToken: googleAuth.idToken,
      );

      UserCredential result = await _auth.signInWithCredential(credential);
      return result.user;
    } catch (e) {
      print(e.toString());
      return null;
    }
  }

  // This main is for demonstration of the function logic.
  // In a real app, Firebase.initializeApp() would be called once at app start.
  static void main() async {
    // Simulate Firebase being initialized
    // await Firebase.initializeApp(); 
    
    GoogleAuthService auth = GoogleAuthService();
    User? user = await auth.signInWithGoogle();
    if (user != null) {
      print("Signed in with Google: ${user.email}");
    } else {
      print("Google Sign-In failed or cancelled.");
    }
  }
}

Firebase Auth Quick Check

When should Firebase.initializeApp() be called in a Flutter application to ensure all Firebase services are ready?

Recap & Next Steps

Congratulations! You've learned the essentials of integrating Firebase into your Flutter app and setting up authentication.

We covered:

  • Setting up a Firebase project and adding your Flutter app.
  • Adding Firebase dependencies and initializing Firebase Core.
  • Implementing Email/Password sign-up and sign-in.
  • Monitoring user authentication state changes.
  • Setting up and implementing Google Sign-In.

These are fundamental steps for building secure and interactive Flutter applications with Firebase. Next, you'll explore Cloud Firestore for database integration!

常见问题解答

「Firebase 配置与身份验证」课时是免费的吗？

是的 — 「Firebase 配置与身份验证」的完整文本可在网页上免费阅读。要进行交互式练习（内置代码编辑器和全天候 AI 导师）并解锁 Flutter Mobile Development 课程的其余内容，请升级到 CoddyKit PRO。 Flutter Mobile Development 课程共包含 4 节课。

「Firebase 配置与身份验证」这节课中我会学到什么？

在 Flutter 项目中配置 Firebase，并使用电子邮件/密码、Google 登录和其他提供商实现用户身份验证。 你通过在浏览器中直接运行的动手代码来练习 Flutter Mobile Development，全天候 AI 导师会在你学习这节课的过程中回答你的问题。

学习 Flutter Mobile Development 需要有经验吗？

无需任何先前经验。CoddyKit 上的 Flutter Mobile Development 课程适合初学者到高级学习者，你可以从这里开始或从头开始，按照自己的节奏学习。 这是第 1 节课，共 4 节。

「Firebase 配置与身份验证」课时需要多长时间？

大多数 CoddyKit 课程大约需要 5–10 分钟。每节课都很精短且互动，所以你能稳步进步，并在网页和应用中从离开的地方继续。

我能在这节 Flutter Mobile Development 课中编写并运行代码吗？

能。每节 Flutter Mobile Development 课都包含内置代码编辑器，你可以在浏览器中直接编写并运行真实代码，并获得即时 AI 反馈 — 无需本地设置。

此课程中的所有课时

  1. Firebase 配置与身份验证
  2. Cloud Firestore 数据库
  3. 云存储与云函数
  4. Firebase 云消息传递与通知
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