Firebase with Flutter - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize Firebase in a Flutter app.

Firebase

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase[1]();
  runApp(MyApp());
}

Drag options to blanks, or click blank then click option'

AinitializeApp

BstartApp

CinitFirebase

DsetupFirebase

Attempts:

3 left

💡 Hint

Common Mistakes

Using non-existent methods like startApp or setupFirebase.

Forgetting to call ensureInitialized before initializing Firebase.

The correct method to initialize Firebase in Flutter is initializeApp().

2fill in blank

medium

Complete the code to get an instance of Firestore in Flutter.

Firebase

final FirebaseFirestore firestore = FirebaseFirestore.[1];

Drag options to blanks, or click blank then click option'

AfirestoreInstance

BgetInstance

CgetFirestore

Dinstance

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to call getInstance() which does not exist in Flutter Firestore.

Using incorrect method names like getFirestore.

The correct way to get Firestore instance is using the instance getter.

3fill in blank

hard

Fix the error in the code to add a document to Firestore collection.

Firebase

await firestore.collection('users').[1]({'name': 'Alice', 'age': 25});

Drag options to blanks, or click blank then click option'

Aadd

BaddDocument

Cinsert

Dcreate

Attempts:

3 left

💡 Hint

Common Mistakes

Using non-existent methods like addDocument or insert.

Confusing with create which is not a Firestore method.

The correct method to add a document to a collection is add().

4fill in blank

hard

Fill both blanks to read a document from Firestore and print its data.

Firebase

DocumentSnapshot snapshot = await firestore.collection('users').[1]('user123').[2]();
print(snapshot.data());

Drag options to blanks, or click blank then click option'

Adoc

Bget

Cdocument

Dfetch

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'document' instead of 'doc' which is deprecated.

Using 'fetch' which is not a Firestore method.

Use doc() to specify the document and get() to fetch it.

5fill in blank

hard

Fill all three blanks to update a Firestore document with new data.

Firebase

await firestore.collection('users').[1]('user123').[2]([3]);

Drag options to blanks, or click blank then click option'

Adoc

Bupdate

C{'age': 26}

Dset

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'set' instead of 'update' which overwrites the whole document.

Passing data as a string instead of a map.

Use doc() to select the document, update() to modify it, and pass the new data as a map.

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