Flutter Firebase app: Implement Google Sign-In

Let’s create a Flutter Firebase app and connect Firebase to the Flutter project. This is crucial, especially if you plan to use Firebase services like authentication, Firestore, or Firebase Cloud Messaging. Here’s a guide on how to connect Firebase in a Flutter project:

Step 1: Create a Firebase project

1. Go to the Firebase Console.
2. Click on “Add Project”.
3. Follow the instructions to create a new project.
4. Once the project is created, click on “Continue”.

Step 2: Register your app with Firebase

1. After creating the project, click on “Add app”.
2. Choose the appropriate platform (Android or iOS) and follow the setup instructions.

• For Android:
• Android package name: Your Flutter project’s package name (e.g., com.example.myapp).
• Optionally, you can add a nickname for this app.
• Click on “Register app”.
• Download the google-services.json file and place it inside the android/app directory in your Flutter project.
• For iOS:
• iOS bundle ID: Your Flutter project’s iOS bundle ID (e.g., com.example.myapp).
• Optionally, you can add a nickname for this app.
• Click on “Register app”.
• Download the GoogleService-Info.plist file and add it to the ios/Runner directory in your Flutter project.

Step 3: Add Firebase SDK to your Flutter project

1. Open your Flutter project in an IDE (e.g., Visual Studio Code).
2. Add the Firebase SDK to your Flutter app:

• Open the pubspec.yaml file.
• Add the firebase_core and any other Firebase packages you intend to use. For example:

dependencies:
  flutter:
    sdk: flutter
  firebase_core: ^1.0.0
  firebase_auth: ^3.0.0  # If you plan to use Firebase Authentication
  cloud_firestore: ^3.0.0  # If you plan to use Firestore

• Save the file.
  Run flutter pub get to install the dependencies.

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Step 4: Initialize Firebase in your Flutter app

1. Open your main.dart file.
2. Import the necessary packages:

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

Initialize Firebase in the main() function before running the app:

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

Ensure you add the Google services plugin at the bottom of the android/app/build.gradle file (just before the last line }):

apply plugin: 'com.google.gms.google-services'

On iOS, ensure you add the following in the ios/Runner/AppDelegate.swift file:

import UIKit
import Flutter
import Firebase

@UIApplicationMain
@objc class AppDelegate: FlutterAppDelegate {
  override func application(
    _ application: UIApplication,
    didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
  ) -> Bool {
    FirebaseApp.configure()
    return super.application(application, didFinishLaunchingWithOptions: launchOptions)
  }
}

Step 5: Usage

After these steps, Firebase is now connected to your Flutter project, and you can start using Firebase services such as Authentication, Firestore, etc., in your Flutter app.

Here’s an example of how to use Google Sign-In with Firebase Authentication in your Flutter app:

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

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

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

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  final FirebaseAuth _auth = FirebaseAuth.instance;
  final GoogleSignIn googleSignIn = GoogleSignIn();

  Future<User?> _handleSignIn() async {
    try {
      final GoogleSignInAccount? googleSignInAccount = await googleSignIn.signIn();
      final GoogleSignInAuthentication googleSignInAuthentication = await googleSignInAccount!.authentication;

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

      final UserCredential authResult = await _auth.signInWithCredential(credential);
      final User? user = authResult.user;

      assert(!user!.isAnonymous);
      assert(await user!.getIdToken() != null);

      final User? currentUser = await _auth.currentUser;
      assert(user!.uid == currentUser!.uid);

      print('signInWithGoogle succeeded: $user');

      return user;
    } catch (error) {
      print(error);
      return null;
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Flutter Medium App'),
      ),
      body: Center(
        child: ElevatedButton(
          onPressed: () {
            _handleSignIn()
                .then((User? user) => print(user))
                .catchError((e) => print(e));
          },
          child: Text('Sign in with Google'),
        ),
      ),
    );
  }
}

With these steps, Firebase is successfully integrated into your Flutter app, allowing you to use Firebase services such as Authentication, Firestore, etc.