Add Google Sign in to you Flutter app just in few steps

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Following steps might be helpful to achieve.

1. Setting up your project

Setup your Flutter project

2. Adding pub.dev library

firebase_auth
google_sign_in

3. Implement Google Sign in functionality

4. Creating firebase project

Register your android app, which is generally your application Id in your app-level build. Gradle.

Download the google-services.json. Move the downloaded google-serivces.json file into your Android app module root directory.

• Add your project-level build.gradle file.

dependencies {
    classpath 'com.android.tools.build:gradle:3.5.0'
    classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
classpath 'com.google.gms:google-services:4.3.3'
}

• Add to your project app-level build. Gradle file

dependencies {
    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
    implementation 'com.google.firebase:firebase-analytics:17.2.2'}
apply plugin: 'com.google.gms.google-services'

Set up the sign-in method.

Project name and support email.

Go to project settings and then open the general tab.

Add the SHA key.

5. Getting SHA-1 key

To generate SHA key please follow this link https://developers.google.com/android/guides/client-auth

7. Adding google authentication

create an instance of GoogleSignIn.

final FirebaseAuth _auth = FirebaseAuth.instance;
final GoogleSignIn _googleSignIn = GoogleSignIn();

8. Testing our app functionality

Add this code to your main.dart file and run and test it

import 'package:flutter/material.dart';
import 'package:google_sign_in/google_sign_in.dart';
void main() {
  runApp(const MaterialApp(
    home: Home(),
  ));
}
final GoogleSignIn _googleSignIn = GoogleSignIn(scopes: ['email']);
class Home extends StatefulWidget {
  const Home({Key? key}) : super(key: key);
@override
  _HomeState createState() => _HomeState();
}
class _HomeState extends State<Home> {
  GoogleSignInAccount? _currentUser;
@override
  void initState() {
    _googleSignIn.onCurrentUserChanged.listen((account) {
      setState(() {
        _currentUser = account;
      });
    });
    _googleSignIn.signInSilently();
    super.initState();
  }
@override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Flutter Google Sign in'),
      ),
      body: Container(
        alignment: Alignment.center,
        child: _buildWidget(),
      ),
    );
  }
Widget _buildWidget() {
    GoogleSignInAccount? user = _currentUser;
    if (user != null) {
      return Padding(
        padding: const EdgeInsets.fromLTRB(2, 12, 2, 12),
        child: Column(
          children: [
            ListTile(
              leading: GoogleUserCircleAvatar(identity: user),
              title: Text(
                user.displayName ?? '',
                style: TextStyle(fontSize: 22),
              ),
              subtitle: Text(user.email, style: TextStyle(fontSize: 22)),
            ),
            const SizedBox(
              height: 20,
            ),
            const Text(
              'Signed in successfully',
              style: TextStyle(fontSize: 20),
            ),
            const SizedBox(
              height: 10,
            ),
            ElevatedButton(onPressed: signOut, child: const Text('Sign out'))
          ],
        ),
      );
    } else {
      return Padding(
        padding: const EdgeInsets.all(12.0),
        child: Column(
          children: [
            const SizedBox(
              height: 20,
            ),
            const Text(
              'You are not signed in',
              style: TextStyle(fontSize: 30),
            ),
            const SizedBox(
              height: 10,
            ),
            ElevatedButton(
                onPressed: signIn,
                child: const Padding(
                  padding: EdgeInsets.all(8.0),
                  child: Text('Sign in', style: TextStyle(fontSize: 30)),
                )),
          ],
        ),
      );
    }
  }
void signOut() {
    _googleSignIn.disconnect();
  }
Future<void> signIn() async {
    try {
      await _googleSignIn.signIn();
    } catch (e) {
      print('Error signing in $e');
    }
  }
}