Why Firebase provides backend services in Flutter - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize Firebase in a Flutter app.

Flutter

await Firebase.[1]();

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

AstartApp

BinitializeApp

CrunApp

DlaunchApp

Attempts:

3 left

💡 Hint

Common Mistakes

Using runApp instead of initializeApp

Calling startApp which does not exist

Firebase apps start by calling initializeApp() to set up backend services.

2fill in blank

medium

Complete the code to add a document to Firestore database.

Flutter

FirebaseFirestore.instance.collection('users').[1]({'name': 'Anna'});

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

Aadd

Bget

Cupdate

Ddelete

Attempts:

3 left

💡 Hint

Common Mistakes

Using get which reads data

Using update which modifies existing data

The add() method adds a new document to a Firestore collection.

3fill in blank

hard

Fix the error in the code to listen for authentication state changes.

Flutter

FirebaseAuth.instance.authStateChanges().[1]((User? user) {
  if (user == null) {
    print('User signed out');
  } else {
    print('User signed in');
  }
});

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

AonChange

Bsubscribe

Clisten

Dwatch

Attempts:

3 left

💡 Hint

Common Mistakes

Using subscribe which is not a Dart Stream method

Using onChange which does not exist

The listen() method subscribes to stream events like auth state changes.

4fill in blank

hard

Fill both blanks to create a map of user IDs to their email addresses from a list.

Flutter

var userMap = {user.[1]: user.[2] for user in users};

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

Auid

Bemail

Cname

Did

Attempts:

3 left

💡 Hint

Common Mistakes

Using name or id which are not standard Firebase user properties

Each user object has a unique ID as uid and an email as email.

5fill in blank

hard

Fill all three blanks to filter and map Firestore documents with age over 18.

Flutter

var adults = {doc.[1]: doc.data()[[2]] for doc in snapshot.docs if doc.data()[[3]] > 18};

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

Aid

B'age'

C'name'

Ddata

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up field names or using data instead of id for keys

Use id for document ID, 'name' for mapping, and filter by 'age' field.

Practice

1. Why does Firebase provide backend services for mobile apps?

easy

A. To make apps run only on Android devices

B. To replace the need for frontend development

C. To save developers time by handling server tasks

D. To increase the app size significantly

Solution

1. Step 1: Understand Firebase's purpose

   Firebase offers backend services like database and authentication to simplify app development.

2. Step 2: Identify the benefit for developers

   This means developers don't need to build and maintain their own servers, saving time and effort.

3. Final Answer:

   To save developers time by handling server tasks -> Option C

4. Quick Check:

   Firebase backend services = save developer time [OK]

Hint: Firebase backend means less server work for developers [OK]

Common Mistakes:

• Thinking Firebase only works on Android
• Believing Firebase replaces frontend coding
• Assuming Firebase increases app size

2. Which of the following is the correct way to initialize Firebase in a Flutter app?

easy

A. Firebase.initializeApp();

B. Firebase.start();

C. Firebase.runApp();

D. Firebase.launch();

Solution

1. Step 1: Recall Firebase initialization method

   The official method to start Firebase in Flutter is Firebase.initializeApp().

2. Step 2: Check other options

   Other options like start(), runApp(), or launch() are not valid Firebase methods.

3. Final Answer:

   Firebase.initializeApp(); -> Option A

4. Quick Check:

   Initialize Firebase = initializeApp() [OK]

Hint: Firebase starts with initializeApp() method [OK]

Common Mistakes:

• Using non-existent Firebase.start() method
• Confusing with Flutter's runApp()
• Trying Firebase.launch() which doesn't exist

3. Consider this Flutter code snippet using Firebase Firestore:

var doc = FirebaseFirestore.instance.collection('users').doc('user1');
var snapshot = await doc.get();
print(snapshot.exists);

What will be printed if the document 'user1' exists in the 'users' collection?

medium

A. An error message

B. false

C. null

D. true

Solution

1. Step 1: Understand Firestore document retrieval

   The get() method fetches the document snapshot; snapshot.exists is true if document exists.

2. Step 2: Check the condition for printing

   If 'user1' document exists, snapshot.exists will be true, so print outputs true.

3. Final Answer:

   true -> Option D

4. Quick Check:

   Document exists? snapshot.exists = true [OK]

Hint: snapshot.exists is true if document is found [OK]

Common Mistakes:

• Assuming snapshot.exists returns document data
• Expecting false even if document exists
• Confusing snapshot.exists with snapshot.data

4. This Flutter code tries to sign in a user with Firebase Authentication:

await FirebaseAuth.instance.signInWithEmailAndPassword(email: email, password: password);
print('User signed in');

But the app crashes with an error about missing initialization. What is the likely fix?

medium

A. Call Firebase.initializeApp() before sign-in

B. Remove the await keyword

C. Use signInWithGoogle() instead

D. Change print to debugPrint

Solution

1. Step 1: Identify the error cause

   Firebase services require initialization before use; missing Firebase.initializeApp() causes crash.

2. Step 2: Apply the fix

   Adding Firebase.initializeApp() before calling signInWithEmailAndPassword fixes the initialization error.

3. Final Answer:

   Call Firebase.initializeApp() before sign-in -> Option A

4. Quick Check:

   Initialize Firebase before auth calls [OK]

Hint: Always initialize Firebase before using its services [OK]

Common Mistakes:

• Removing await which is needed for async calls
• Using wrong sign-in method without setup
• Thinking print method causes crash

5. You want to build a Flutter app that shows live chat messages updating instantly. Why is Firebase a good backend choice for this?

hard

A. Firebase requires you to write your own server code for syncing

B. Firebase provides real-time database syncing without manual server setup

C. Firebase only supports batch data updates, not real-time

D. Firebase does not support user authentication

Solution

1. Step 1: Understand real-time data needs

   Live chat requires instant updates to all users without delay.

2. Step 2: Match Firebase features

   Firebase Realtime Database and Firestore sync data instantly and handle user auth easily without server code.

3. Final Answer:

   Firebase provides real-time database syncing without manual server setup -> Option B

4. Quick Check:

   Real-time sync + no server code = Firebase [OK]

Hint: Firebase = real-time data + easy auth without servers [OK]

Common Mistakes:

• Thinking Firebase needs manual server code
• Believing Firebase lacks real-time support
• Assuming Firebase can't handle user login