Firebase Authentication in Android Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize Firebase Authentication in an Android Kotlin app.

Android Kotlin

private lateinit var auth: FirebaseAuth

override fun onCreate(savedInstanceState: Bundle?) {
  super.onCreate(savedInstanceState)
  auth = FirebaseAuth.[1]()
}

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

Astart

BgetInstance

Ccreate

Dinitialize

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'initialize' instead of 'getInstance' causes errors.

Trying to create a new FirebaseAuth object directly.

You use FirebaseAuth.getInstance() to get the Firebase Authentication object.

2fill in blank

medium

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

Android Kotlin

auth.signInWithEmailAndPassword(email, password)
  .addOnCompleteListener { task ->
    if (task.[1]()) {
      // Sign in success
    } else {
      // Sign in failed
    }
  }

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

AisDone

BisComplete

CisSuccessful

DisSuccess

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'isComplete' which only means the task finished, not success.

Using 'isDone' or 'isSuccess' which do not exist.

The isSuccessful() method checks if the sign-in task succeeded.

3fill in blank

hard

Fix the error in the code to send a password reset email using Firebase Authentication.

Android Kotlin

auth.[1](userEmail)
  .addOnCompleteListener { task ->
    if (task.isSuccessful) {
      // Email sent
    }
  }

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

AsendPasswordResetEmail

BresetPasswordEmail

CpasswordResetSend

DsendResetEmail

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect method names causes compile errors.

Trying to call a method that does not exist.

The correct method to send a password reset email is sendPasswordResetEmail().

4fill in blank

hard

Fill both blanks to create a new user with email and password and handle success or failure.

Android Kotlin

auth.[1](email, password)
  .addOnCompleteListener { task ->
    if (task.[2]()) {
      // User created
    } else {
      // Creation failed
    }
  }

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

AcreateUserWithEmailAndPassword

BsignInWithEmailAndPassword

CisSuccessful

DisComplete

Attempts:

3 left

💡 Hint

Common Mistakes

Using signIn method instead of createUser method.

Checking 'isComplete' instead of 'isSuccessful'.

Use createUserWithEmailAndPassword to create a user and check isSuccessful() to confirm success.

5fill in blank

hard

Fill all three blanks to get the current user, check if signed in, and get their email.

Android Kotlin

val user = auth.[1]
if (user != null) {
  val email = user.[2]
  println("User email: [3]")
}

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

AcurrentUser

Bemail

C$email

DgetCurrentUser

Attempts:

3 left

💡 Hint

Common Mistakes

Using a method instead of property for current user.

Trying to call a method to get email instead of property.

You get the current user with currentUser, access their email property, and print it.

Practice

1. What is the main purpose of Firebase Authentication in an Android app?

easy

A. To store user data in a database

B. To send push notifications to users

C. To design the app's user interface

D. To securely manage user sign-in and registration

Solution

1. Step 1: Understand Firebase Authentication role

   Firebase Authentication is designed to handle user sign-in and registration securely.

2. Step 2: Differentiate from other Firebase services

   It does not store user data (that's Firestore/Realtime Database), nor handle UI design or notifications.

3. Final Answer:

   To securely manage user sign-in and registration -> Option D

4. Quick Check:

   Firebase Authentication = Secure sign-in [OK]

Hint: Remember Firebase Auth is for user sign-in only [OK]

Common Mistakes:

• Confusing Authentication with database storage
• Thinking it handles UI design
• Assuming it manages notifications

2. Which Kotlin code snippet correctly registers a new user with email and password using Firebase Authentication?

easy

A. firebaseAuth.registerUser(email, password).addOnCompleteListener { ... }

B. firebaseAuth.signInWithEmailAndPassword(email, password).addOnCompleteListener { ... }

C. firebaseAuth.createUserWithEmailAndPassword(email, password).addOnCompleteListener { ... }

D. firebaseAuth.createUser(email, password).addOnCompleteListener { ... }

Solution

1. Step 1: Identify correct Firebase method for registration

   The method to register a new user is createUserWithEmailAndPassword(email, password).

2. Step 2: Check method names in options

   registerUser and createUser do not exist. signInWithEmailAndPassword is for signing in existing users, not registration.

3. Final Answer:

   firebaseAuth.createUserWithEmailAndPassword(email, password).addOnCompleteListener { ... } -> Option C

4. Quick Check:

   Register new user = createUserWithEmailAndPassword [OK]

Hint: Register uses createUserWithEmailAndPassword method [OK]

Common Mistakes:

• Using signInWithEmailAndPassword to register
• Using non-existent methods like createUser or registerUser
• Confusing method names

3. Given this Kotlin code snippet, what will be printed if the user is signed in?

val user = firebaseAuth.currentUser
if (user != null) {
    println("User is signed in")
} else {
    println("No user signed in")
}

medium

A. User is signed in

B. NullPointerException error

C. No user signed in

D. Compilation error

Solution

1. Step 1: Understand currentUser property

   firebaseAuth.currentUser returns the current signed-in user or null if none.

2. Step 2: Analyze the if condition

   If user is not null, it prints "User is signed in"; otherwise, "No user signed in".

3. Final Answer:

   User is signed in -> Option A

4. Quick Check:

   currentUser != null means user signed in [OK]

Hint: currentUser null means no user; else signed in [OK]

Common Mistakes:

• Assuming currentUser throws error if null
• Confusing sign-in check logic
• Expecting compilation errors incorrectly

4. Identify the error in this Kotlin code for signing out a user:

firebaseAuth.signOut
println("User signed out")

medium

A. signOut is not a FirebaseAuth method

B. Missing parentheses after signOut method

C. println should be inside a callback

D. No error, code is correct

Solution

1. Step 1: Check signOut method usage

   signOut is a method and requires parentheses: signOut()

2. Step 2: Verify other options

   signOut exists in FirebaseAuth; println can be outside callback; so only missing parentheses is error.

3. Final Answer:

   Missing parentheses after signOut method -> Option B

4. Quick Check:

   signOut() needs parentheses [OK]

Hint: Methods need () even if no parameters [OK]

Common Mistakes:

• Forgetting parentheses on method calls
• Thinking signOut is a property
• Assuming println must be in callback

5. You want to create a function in Kotlin that registers a user and then immediately signs them in using Firebase Authentication. Which code snippet correctly does this?

hard

A. firebaseAuth.createUserWithEmailAndPassword(email, password).addOnCompleteListener { task -> if (task.isSuccessful) { println("User registered and signed in") } }

B. firebaseAuth.signInWithEmailAndPassword(email, password).addOnCompleteListener { task -> if (task.isSuccessful) { println("User registered and signed in") } }

C. firebaseAuth.createUserWithEmailAndPassword(email, password).addOnCompleteListener { task -> if (task.isSuccessful) { firebaseAuth.signInWithEmailAndPassword(email, password) } }

D. firebaseAuth.createUserWithEmailAndPassword(email, password).addOnCompleteListener { task -> if (task.isSuccessful) { firebaseAuth.signOut() } }

Solution

1. Step 1: Understand createUserWithEmailAndPassword behavior

   This method registers and automatically signs in the user if successful.

2. Step 2: Analyze options for correct flow

   createUserWithEmailAndPassword(...).addOnCompleteListener { task -> if (task.isSuccessful) { println("User registered and signed in") } } registers and confirms success. signInWithEmailAndPassword only signs in existing users. Calling signIn after createUser is redundant. Calling signOut after is incorrect.

3. Final Answer:

   firebaseAuth.createUserWithEmailAndPassword(email, password).addOnCompleteListener { task -> if (task.isSuccessful) { println("User registered and signed in") } } -> Option A

4. Quick Check:

   Registration auto signs in [OK]

Hint: Register auto signs in; no need to call signIn after [OK]

Common Mistakes:

• Calling signIn after createUserWithEmailAndPassword unnecessarily
• Using signIn without registering first
• Signing out immediately after registration