Firebase Authentication in iOS Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

What happens after a successful Firebase email/password sign-in?

Consider this Swift code snippet for Firebase Authentication sign-in:

Auth.auth().signIn(withEmail: email, password: password) { authResult, error in
  if let user = authResult?.user {
    print("User signed in: \(user.email ?? "unknown")")
  } else {
    print("Sign-in failed")
  }
}

What will be printed if the sign-in is successful?

iOS Swift

Auth.auth().signIn(withEmail: email, password: password) { authResult, error in
  if let user = authResult?.user {
    print("User signed in: \(user.email ?? \"unknown\")")
  } else {
    print("Sign-in failed")
  }
}

A User signed in: [e-mail]

B Sign-in failed

C User signed in: unknown

D No output printed

💡 Hint

Check what the 'user.email' property contains after successful sign-in.

When sign-in succeeds, 'authResult?.user' is non-nil and 'user.email' contains the signed-in user's email. The print statement outputs that email.

🧠 Conceptual

intermediate

What error is returned if Firebase sign-in is attempted with wrong password?

In Firebase Authentication for iOS, if a user tries to sign in with an email that exists but enters the wrong password, what error code will the completion handler receive?

A AuthErrorCode.networkError

B AuthErrorCode.userNotFound

C AuthErrorCode.invalidEmail

D AuthErrorCode.wrongPassword

💡 Hint

Think about the error that specifically means the password is incorrect.

Firebase returns 'AuthErrorCode.wrongPassword' when the password does not match the stored password for the email.

❓ lifecycle

advanced

When is the Firebase Auth state listener triggered?

Given this Swift code:

Auth.auth().addStateDidChangeListener { auth, user in
  if let user = user {
    print("User is signed in: \(user.uid)")
  } else {
    print("No user signed in")
  }
}

At which moments will this listener be called?

iOS Swift

Auth.auth().addStateDidChangeListener { auth, user in
  if let user = user {
    print("User is signed in: \(user.uid)")
  } else {
    print("No user signed in")
  }
}

A Only when the user signs in

B When the app starts and whenever the user signs in or out

C Only when the user signs out

D Only when the app is terminated

💡 Hint

Think about when the authentication state changes.

The listener triggers immediately on adding and whenever the user signs in or out, reflecting current auth state.

📝 Syntax

advanced

What is the correct way to create a new Firebase user with email and password?

Which of the following Swift code snippets correctly creates a new user with Firebase Authentication?

A

Auth.auth().createUser(withEmail: email, password: password) { authResult, error in
  if let user = authResult?.user {
    print("User created: \(user.email ?? "")")
  }
}

B

Auth.auth().signUp(withEmail: email, password: password) { authResult, error in
  print("User created")
}

C

Auth.auth().createUser(email: email, password: password) { authResult, error in
  print("User created")
}

D

Auth.createUser(withEmail: email, password: password) { user, error in
  print("User created")
}

💡 Hint

Check the exact method name and parameters in Firebase iOS SDK.

The correct method is 'createUser(withEmail:password:completion:)' on 'Auth.auth()'. Other options use wrong method names or signatures.

🔧 Debug

expert

Why does this Firebase sign-out code cause a crash?

Consider this Swift code snippet:

try? Auth.auth().signOut()
print("User signed out")

Sometimes this code crashes the app. What is the most likely cause?

iOS Swift

try? Auth.auth().signOut()
print("User signed out")

A Firebase requires a completion handler for signOut()

B The print statement is called before signOut completes

C The signOut() method can throw an error that is not handled properly

D The Auth object is nil causing a crash

💡 Hint

Check how Swift handles errors from throwing functions.

signOut() is a throwing method. Using 'try?' ignores errors but if an error occurs, it can cause unexpected behavior or crash if not handled properly.