UserDefaults for simple values in iOS Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

What is the output after saving and retrieving a value with UserDefaults?

Consider this Swift code that saves a string to UserDefaults and then retrieves it. What will be printed?

iOS Swift

let defaults = UserDefaults.standard
let key = "username"
defaults.set("Alice", forKey: key)
if let name = defaults.string(forKey: key) {
  print(name)
} else {
  print("No value")
}

A Alice

B No value

C nil

D Crash due to missing key

💡 Hint

UserDefaults stores simple values persistently and can retrieve them by the same key.

The code saves the string "Alice" under the key "username" and then retrieves it successfully, so it prints "Alice".

📝 Syntax

intermediate

Which option correctly saves an integer to UserDefaults?

You want to save the integer 42 to UserDefaults under the key "score". Which code snippet does this correctly?

A UserDefaults.standard.setInt(42, forKey: "score")

B UserDefaults.standard["score"] = 42

C UserDefaults.set(42, forKey: "score")

D UserDefaults.standard.set(42, forKey: "score")

💡 Hint

Use the standard UserDefaults instance and the set(_:forKey:) method.

Option D uses the correct method and instance to save an integer value to UserDefaults.

❓ lifecycle

advanced

When are UserDefaults values saved to disk?

You save a value to UserDefaults using set(_:forKey:). When is this value guaranteed to be saved to disk?

A Never saved automatically; must call save() explicitly

B When the app terminates or goes to background

C Only when synchronize() is called

D Immediately after calling set(_:forKey:)

💡 Hint

UserDefaults batches writes for efficiency and saves at certain app lifecycle events.

UserDefaults automatically saves changes when the app goes to background or terminates. The synchronize() method is deprecated and not needed.

🔧 Debug

advanced

Why does retrieving a saved Bool from UserDefaults return false unexpectedly?

This code saves a Bool value true but later retrieving it returns false. What is the likely cause? let defaults = UserDefaults.standard defaults.set(true, forKey: "isLoggedIn") let loggedIn = defaults.bool(forKey: "isLoggedIn") print(loggedIn)

A The key "isLoggedIn" was never saved before retrieval

B The value was saved but the retrieval key is misspelled

C UserDefaults.bool(forKey:) returns false if the key does not exist

D UserDefaults cannot store Bool values

💡 Hint

Check if the key exists before relying on bool(forKey:).

bool(forKey:) returns false if the key does not exist, so if the value was not saved or the key is wrong, it returns false by default.

🧠 Conceptual

expert

What is the best practice for storing sensitive data in UserDefaults?

You want to store a user's password securely. Which statement is true about storing it in UserDefaults?

A UserDefaults is not secure; use Keychain for sensitive data instead

B UserDefaults encrypts data automatically, so it's safe for passwords

C Storing passwords in UserDefaults is fine if the app uses HTTPS

D UserDefaults is secure and recommended for storing passwords

💡 Hint

Think about data encryption and security best practices on iOS.

UserDefaults stores data in plain text and is not encrypted. Sensitive data like passwords should be stored in the Keychain, which is designed for secure storage.