How to Use Firebase Auth in Flutter: Simple Guide

To use FirebaseAuth in Flutter, first add the firebase_auth package and initialize Firebase in your app. Then, use FirebaseAuth.instance to sign up, sign in, or sign out users with methods like createUserWithEmailAndPassword and signInWithEmailAndPassword.

Syntax

Here is the basic syntax to use Firebase Authentication in Flutter:

• FirebaseAuth.instance: Access the Firebase Auth service.
• createUserWithEmailAndPassword(email, password): Register a new user.
• signInWithEmailAndPassword(email, password): Sign in an existing user.
• signOut(): Log out the current user.

dart

final FirebaseAuth auth = FirebaseAuth.instance;

// Register user
await auth.createUserWithEmailAndPassword(
  email: '[e-mail]',
  password: 'password123'
);

// Sign in user
await auth.signInWithEmailAndPassword(
  email: '[e-mail]',
  password: 'password123'
);

// Sign out user
await auth.signOut();

Example

This example shows a simple Flutter app that lets a user sign in with email and password using Firebase Auth.

dart

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

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: SignInPage(),
    );
  }
}

class SignInPage extends StatefulWidget {
  @override
  _SignInPageState createState() => _SignInPageState();
}

class _SignInPageState extends State<SignInPage> {
  final FirebaseAuth _auth = FirebaseAuth.instance;
  final TextEditingController _emailController = TextEditingController();
  final TextEditingController _passwordController = TextEditingController();
  String _message = '';

  Future<void> _signIn() async {
    try {
      await _auth.signInWithEmailAndPassword(
        email: _emailController.text.trim(),
        password: _passwordController.text.trim(),
      );
      setState(() {
        _message = 'Signed in successfully!';
      });
    } catch (e) {
      setState(() {
        _message = 'Error: ' + e.toString();
      });
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Firebase Auth Sign In')),
      body: Padding(
        padding: EdgeInsets.all(16),
        child: Column(
          children: [
            TextField(
              controller: _emailController,
              decoration: InputDecoration(labelText: 'Email'),
            ),
            TextField(
              controller: _passwordController,
              decoration: InputDecoration(labelText: 'Password'),
              obscureText: true,
            ),
            SizedBox(height: 20),
            ElevatedButton(
              onPressed: _signIn,
              child: Text('Sign In'),
            ),
            SizedBox(height: 20),
            Text(_message),
          ],
        ),
      ),
    );
  }
}

Output

A Flutter app screen with email and password fields, a 'Sign In' button, and a message area showing success or error after sign in attempt.

Common Pitfalls

Common mistakes when using Firebase Auth in Flutter include:

• Not initializing Firebase before using FirebaseAuth.
• Not handling exceptions from sign-in or sign-up methods.
• Using plain text passwords without validation.
• Forgetting to add firebase_core and firebase_auth packages in pubspec.yaml.

dart

/* Wrong: Using FirebaseAuth before Firebase.initializeApp() */
// final auth = FirebaseAuth.instance; // This causes error if Firebase not initialized

/* Right: Initialize Firebase first */
await Firebase.initializeApp();
final auth = FirebaseAuth.instance;

Quick Reference

Here is a quick summary of key Firebase Auth methods in Flutter:

Method	Description
createUserWithEmailAndPassword(email, password)	Register a new user with email and password
signInWithEmailAndPassword(email, password)	Sign in an existing user
signOut()	Sign out the current user
currentUser	Get the currently signed-in user
sendPasswordResetEmail(email)	Send password reset email

Key Takeaways

Always initialize Firebase with Firebase.initializeApp() before using FirebaseAuth.

Use FirebaseAuth.instance to access authentication methods like signIn and signUp.

Handle errors with try-catch to manage sign-in failures gracefully.

Add firebase_core and firebase_auth packages to your Flutter project dependencies.

Validate user input before calling authentication methods for better user experience.