Firebase with Flutter - Mini Project: Build & Apply

Firebase with Flutter

📖 Scenario: You are building a simple Flutter app that connects to Firebase to store and retrieve user messages. This app will help you understand how to set up Firebase in Flutter and perform basic database operations.

🎯 Goal: Create a Flutter app that connects to Firebase, initializes Firebase, and writes and reads a simple message from Firestore.

📋 What You'll Learn

Initialize Firebase in the Flutter app

Create a Firestore instance

Write a message to Firestore

Read the message from Firestore

💡 Why This Matters

🌍 Real World

Many mobile apps use Firebase to store and sync data in real time. This project shows the basic setup to connect Flutter apps to Firebase Firestore.

💼 Career

Understanding Firebase integration with Flutter is valuable for mobile developers building cloud-connected apps.

1

Setup Firebase Initialization

In your Flutter app's main.dart file, import firebase_core package and initialize Firebase inside the main() function by calling WidgetsFlutterBinding.ensureInitialized() and await Firebase.initializeApp(). Create a Future main() function that does this initialization.

Firebase

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

// Initialize Firebase in main function
Future main() async {
  WidgetsFlutterBinding.ensureInitialized();
  // Your code here
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: Center(child: Text('Firebase with Flutter')),
      ),
    );
  }
}

Hint

Remember to import firebase_core and call WidgetsFlutterBinding.ensureInitialized() before initializing Firebase.

2

Create Firestore Instance

Import cloud_firestore package and create a variable called firestore that holds the instance of FirebaseFirestore.instance.

Firebase

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

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

// Create Firestore instance here
final FirebaseFirestore firestore = FirebaseFirestore.instance;

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: Center(child: Text('Firebase with Flutter')),
      ),
    );
  }
}

Hint

Import cloud_firestore and create a final FirebaseFirestore firestore = FirebaseFirestore.instance; variable.

3

Write a Message to Firestore

Inside the MyApp widget, add a method called writeMessage() that uses firestore.collection('messages').doc('msg1').set({'text': 'Hello Firebase!'}) to write a message to Firestore.

Firebase

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

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

final FirebaseFirestore firestore = FirebaseFirestore.instance;

class MyApp extends StatelessWidget {
  Future writeMessage() async {
    // Your code here
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: Center(child: Text('Firebase with Flutter')),
      ),
    );
  }
}

Hint

Use firestore.collection('messages').doc('msg1').set({'text': 'Hello Firebase!'}) inside an async method.

4

Read the Message from Firestore

Add a method called readMessage() inside MyApp that uses firestore.collection('messages').doc('msg1').get() to read the message document. Extract the 'text' field from the document snapshot and return it as a String.

Firebase

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

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

final FirebaseFirestore firestore = FirebaseFirestore.instance;

class MyApp extends StatelessWidget {
  Future writeMessage() async {
    await firestore.collection('messages').doc('msg1').set({'text': 'Hello Firebase!'});
  }

  Future readMessage() async {
    // Your code here
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: Center(child: Text('Firebase with Flutter')),
      ),
    );
  }
}

Hint

Use await firestore.collection('messages').doc('msg1').get() and return the 'text' field.

Practice

1. What is the main purpose of initializing Firebase in a Flutter app?

easy

A. To compile the Flutter app into native code

B. To connect the app to Firebase backend services

C. To design the app's user interface

D. To create local storage on the device

Solution

1. Step 1: Understand Firebase initialization

   Initializing Firebase sets up the connection between the Flutter app and Firebase backend services like Authentication and Firestore.

2. Step 2: Identify the purpose of initialization

   Without initialization, the app cannot use Firebase features because it is not linked to Firebase servers.

3. Final Answer:

   To connect the app to Firebase backend services -> Option B

4. Quick Check:

   Firebase initialization = Connect app to backend [OK]

Hint: Firebase init links app to backend services [OK]

Common Mistakes:

• Thinking initialization designs UI
• Confusing initialization with app compilation
• Assuming initialization creates local storage

2. Which code snippet correctly initializes Firebase in a Flutter app?

easy

A. FirebaseApp.initialize();

B. Firebase.initApp();

C. await Firebase.initializeApp();

D. initializeFirebase();

Solution

1. Step 1: Recall Firebase initialization syntax

   The official method to initialize Firebase in Flutter is calling await Firebase.initializeApp();

2. Step 2: Check other options for correctness

   Other options use incorrect method names or missing await keyword, causing errors.

3. Final Answer:

   await Firebase.initializeApp(); -> Option C

4. Quick Check:

   Correct Firebase init syntax = await Firebase.initializeApp() [OK]

Hint: Use await Firebase.initializeApp() to init Firebase [OK]

Common Mistakes:

• Omitting await keyword
• Using wrong method names
• Calling initialization without async context

3. Given this Flutter code using Firebase Authentication, what will be printed if the user signs in successfully?

try {
  UserCredential user = await FirebaseAuth.instance.signInWithEmailAndPassword(email: '[e-mail]', password: '123456');
  print('User signed in: ' + user.user!.email!);
} catch (e) {
  print('Sign in failed');
}

medium

A. User signed in: [e-mail]

B. Sign in failed

C. User signed in: null

D. No output

Solution

1. Step 1: Analyze successful sign-in flow

   If signInWithEmailAndPassword succeeds, it returns a UserCredential with a non-null user and email.

2. Step 2: Understand the print statement

   The code prints 'User signed in: ' plus the user's email, which is '[e-mail]'.

3. Final Answer:

   User signed in: [e-mail] -> Option A

4. Quick Check:

   Successful sign-in prints user email [OK]

Hint: Success prints user email, failure prints error [OK]

Common Mistakes:

• Assuming print shows 'Sign in failed' on success
• Expecting null email on success
• Ignoring async await behavior

4. What is wrong with this Flutter Firebase Firestore code snippet?

FirebaseFirestore firestore = FirebaseFirestore.instance;
firestore.collection('users').add({
  'name': 'Alice',
  'age': 25
});
print('User added');

medium

A. Missing await before add() causes no error

B. Firestore instance is not initialized

C. The add() method requires a document ID

D. The print statement is inside the add() call

Solution

1. Step 1: Check Firestore instance usage

   FirebaseFirestore.instance is correctly assigned to firestore, so initialization is fine.

2. Step 2: Analyze add() method and await usage

   add() returns a Future; missing await means the print runs before add completes, but no syntax error occurs.

3. Final Answer:

   Missing await before add() causes no error -> Option A

4. Quick Check:

   Missing await = no error but async issue [OK]

Hint: Always await async Firestore calls to ensure completion [OK]

Common Mistakes:

• Thinking add() needs document ID (it auto-generates)
• Assuming print inside add() call
• Believing Firestore instance is uninitialized

5. You want to build a Flutter app that shows a list of user names from Firestore and updates in real-time. Which approach correctly uses Firebase with Flutter to achieve this?

hard

A. Store user names locally and update Firestore only on app restart

B. Use FutureBuilder with FirebaseFirestore.instance.collection('users').get() to fetch names once

C. Use a Timer to fetch Firestore data every 5 seconds and update UI manually

D. Use StreamBuilder with FirebaseFirestore.instance.collection('users').snapshots() to listen and display names

Solution

1. Step 1: Understand real-time updates in Firestore

   Firestore provides snapshots() streams that emit data changes in real-time.

2. Step 2: Choose Flutter widget for real-time data

   StreamBuilder listens to streams and rebuilds UI on data changes, perfect for real-time Firestore updates.

3. Step 3: Evaluate other options

   FutureBuilder fetches data once, Timer polling is inefficient, and local storage does not reflect real-time changes.

4. Final Answer:

   Use StreamBuilder with FirebaseFirestore.instance.collection('users').snapshots() to listen and display names -> Option D

5. Quick Check:

   Real-time Firestore + StreamBuilder = live UI updates [OK]

Hint: Use StreamBuilder with snapshots() for live Firestore data [OK]

Common Mistakes:

• Using FutureBuilder for real-time data
• Polling Firestore with Timer instead of streams
• Relying on local storage for live updates