Firebase Authentication in Flutter - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize Firebase in a Flutter app.

Flutter

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

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

AstartApp

BinitFirebase

CinitializeApp

DlaunchApp

Attempts:

3 left

💡 Hint

Common Mistakes

Using a method name that does not exist in Firebase.

Forgetting to call ensureInitialized before Firebase initialization.

The method initializeApp() is used to initialize Firebase before running the app.

2fill in blank

medium

Complete the code to sign in a user with email and password.

Flutter

final userCredential = await FirebaseAuth.instance.[1]('[e-mail]', 'password123');

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

AsignInWithEmailAndPassword

BregisterUser

CloginUser

DauthenticateUser

Attempts:

3 left

💡 Hint

Common Mistakes

Using a method that does not exist in FirebaseAuth.

Confusing sign in with registration methods.

The method signInWithEmailAndPassword signs in a user using email and password.

3fill in blank

hard

Fix the error in the code to sign out the current user.

Flutter

await FirebaseAuth.instance.[1]();

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

AsignIn

Blogout

ClogOutUser

DsignOut

Attempts:

3 left

💡 Hint

Common Mistakes

Using non-existent methods like 'logOutUser' or 'logout'.

Using signIn instead of signOut.

The correct method to sign out a user is signOut().

4fill in blank

hard

Fill both blanks to create a new user with email and password.

Flutter

final userCredential = await FirebaseAuth.instance.[1]('[2]', 'mypassword');

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

AcreateUserWithEmailAndPassword

BsignInWithEmailAndPassword

[e-mail]

[e-mail]

Attempts:

3 left

💡 Hint

Common Mistakes

Using signIn method instead of createUser.

Using an invalid email string.

Use createUserWithEmailAndPassword to register a new user, and provide a valid email like [e-mail].

5fill in blank

hard

Fill all three blanks to send a password reset email.

Flutter

await FirebaseAuth.[1].sendPasswordResetEmail(email: '[2]');

print('[3]');

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

Ainstance

[e-mail]

CPassword reset email sent

DcurrentUser

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect FirebaseAuth instance accessor.

Forgetting to provide the email parameter.

Not printing a confirmation message.

Use instance to access FirebaseAuth instance, provide the user's email, and print a confirmation message.

Practice

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

easy

A. To send push notifications to users

B. To securely manage user sign-up and login

C. To design the app's user interface

D. To store user data in a database

Solution

1. Step 1: Understand Firebase Authentication role

   Firebase Authentication helps apps manage user accounts securely.

2. Step 2: Differentiate from other Firebase services

   It does not store user data or handle UI or notifications.

3. Final Answer:

   To securely manage user sign-up and login -> Option B

4. Quick Check:

   Authentication = Secure login [OK]

Hint: Authentication means managing user login securely [OK]

Common Mistakes:

• Confusing authentication with database storage
• Thinking it handles UI design
• Assuming it sends notifications

2. Which Flutter Firebase method is used to sign up a new user with email and password?

easy

A. createUserWithEmailAndPassword

B. signOut

C. signInWithEmailAndPassword

D. sendPasswordResetEmail

Solution

1. Step 1: Identify sign-up method

   The method to create a new user is createUserWithEmailAndPassword.

2. Step 2: Differentiate from sign-in and other methods

   signInWithEmailAndPassword is for login, not sign-up.

3. Final Answer:

   createUserWithEmailAndPassword -> Option A

4. Quick Check:

   Sign-up method = createUserWithEmailAndPassword [OK]

Hint: Sign-up uses createUserWithEmailAndPassword [OK]

Common Mistakes:

• Using signInWithEmailAndPassword for sign-up
• Confusing signOut with sign-up
• Mixing reset email with sign-up

3. What will the following Flutter code print if the user enters correct email and password?

try {
  await FirebaseAuth.instance.signInWithEmailAndPassword(email: '[e-mail]', password: 'pass123');
  print('Login successful');
} catch (e) {
  print('Login failed');
}

medium

A. No output

B. Login failed

C. Syntax error

D. Login successful

Solution

1. Step 1: Analyze try block with correct credentials

   Since email and password are correct, signInWithEmailAndPassword succeeds.

2. Step 2: Check catch block execution

   No error occurs, so catch block is skipped and 'Login successful' prints.

3. Final Answer:

   Login successful -> Option D

4. Quick Check:

   Correct login prints success [OK]

Hint: Correct login prints success message [OK]

Common Mistakes:

• Assuming catch block runs on success
• Thinking syntax error occurs
• Ignoring async/await behavior

4. Identify the error in this Flutter Firebase Authentication code snippet:

final user = await FirebaseAuth.instance.createUserWithEmailAndPassword(email: email, password: password);
print(user.email);

medium

A. createUserWithEmailAndPassword returns UserCredential, not User

B. Email and password parameters are missing

C. print statement syntax is incorrect

D. Await keyword cannot be used here

Solution

1. Step 1: Check return type of createUserWithEmailAndPassword

   This method returns a UserCredential object, not a User directly.

2. Step 2: Access user email correctly

   The email is inside user.user.email, so printing user.email causes error.

3. Final Answer:

   createUserWithEmailAndPassword returns UserCredential, not User -> Option A

4. Quick Check:

   Return type is UserCredential [OK]

Hint: Remember createUserWithEmailAndPassword returns UserCredential [OK]

Common Mistakes:

• Treating UserCredential as User
• Forgetting to access .user property
• Misusing await keyword

5. You want to show a friendly error message when login fails due to wrong password. Which Flutter Firebase Authentication code snippet correctly handles this?

try {
  await FirebaseAuth.instance.signInWithEmailAndPassword(email: email, password: password);
} catch (e) {
  if (e.code == 'wrong-password') {
    print('Incorrect password. Please try again.');
  } else {
    print('Login error: ' + e.message);
  }
}

hard

A. Correctly checks error code and shows message

B. e.code is not available on exception object

C. Should use on FirebaseAuthException catch instead of generic catch

D. print statements should be replaced with throw

Solution

1. Step 1: Understand error handling in Firebase Auth

   FirebaseAuthException provides the code property; generic catch (e) may not.

2. Step 2: Use specific catch for FirebaseAuthException

   Using on FirebaseAuthException catch (e) allows access to e.code safely.

3. Step 3: Evaluate given code

   Given code uses generic catch, so e.code may cause runtime error.

4. Final Answer:

   Should use on FirebaseAuthException catch instead of generic catch -> Option C

5. Quick Check:

   Use FirebaseAuthException catch for error codes [OK]

Hint: Catch FirebaseAuthException to access error codes safely [OK]

Common Mistakes:

• Using generic catch without exception type
• Assuming all exceptions have code property
• Replacing print with throw unnecessarily