Top 40+ iOS Developer Interview Questions

Typical iOS Developer Interview Process

Swift, Memory Management & App Lifecycle

Master Swift's core concepts, ARC memory management, and iOS app lifecycle states. This section is critical for all iOS roles.

• Explain the difference between value types and reference types in Swift. Provide examples.
• What is ARC and how does it prevent memory leaks?

  Interviewer Insight: ARC questions test whether you've tracked down a real retain cycle in Instruments, not whether you can define strong vs weak references. Candidates who've shipped production code mention specific tools—Memory Graph debugger, Allocations instrument—and real scenarios like network callbacks keeping view controllers alive unnecessarily.

  Sample Answer Guidance: ARC tracks strong references to objects automatically; when the count reaches zero, the object deallocates. The limitation is circular references—a closure capturing self while the view controller holds the closure creates a retain cycle preventing both from deallocating. I fix this with [weak self] in closure captures: networkManager.fetch { [weak self] result in self?.updateUI(result) }, allowing deallocation when no external references exist.
• Describe a retain cycle and show how to prevent it with code.

  Sample Answer Guidance: A retain cycle happens when object A holds a strong ref to B, and B holds a strong ref back to A (often via a closure), preventing both from deallocating. Example: a ViewController strong-references a closure that captures self. Fix with [weak self] capture list: timer.start { [weak self] in self?.updateLabel() } ensures the closure doesn't prevent the view controller's deallocation, breaking the cycle.
• What are optionals in Swift? Why are they important?
• Explain Swift protocols and provide a practical example.
• What are generics in Swift? Provide an example with constraints.
• Describe the iOS app lifecycle and the key state transitions.
• What is the difference between strong, weak, and unowned references?

  Sample Answer Guidance: Strong references increase refcount and keep objects alive (use by default). Weak references don't increase count and return nil on deallocation, preventing cycles—ideal for delegate properties: weak var delegate: TableViewDelegate?. Unowned references also don't increase count but assume the object exists; they crash if accessed after deallocation, suitable when the referenced object's lifetime always exceeds the referencing object (e.g., a closure capturing self in a method where self outlives the closure).

Networking, Persistence & App Store

Master URLSession, Codable, Core Data, keychain security, push notifications, and App Store submission requirements.

• How do you use URLSession to make network requests in Swift?
• Explain Codable and its benefits for JSON parsing.
• What is the difference between Core Data and SwiftData?

  Sample Answer Guidance: Core Data is Apple's object-graph management with SQL persistence; models extend NSManagedObject, and you query via NSFetchRequest with NSPredicate filters. SwiftData (iOS 17+) simplifies this: models use Swift classes marked with @Model macro, and querying is more intuitive with Swift syntax. SwiftData is a lightweight wrapper over Core Data offering better developer experience. Choose SwiftData for new iOS 17+ projects; use Core Data for backwards compatibility or legacy codebases.
• How do you securely store sensitive data (passwords, tokens) in iOS?

  Sample Answer Guidance: Use the Keychain (encrypted, OS-managed storage) never UserDefaults or files. Store tokens via SecItemAdd with kSecClass: kSecClassInternetPassword and kSecAttrServer to specify the service. For retrieval, SecItemCopyMatching returns the stored data. I use a wrapper like KeychainAccess (open-source) to simplify the API—it handles encoding/decoding automatically: Keychain(service: "myapp")["user_token"] = token. Never log sensitive values; consider @SecureString properties to prevent accidental exposure.
• Explain push notifications in iOS. How do you implement remote notifications?

  Sample Answer Guidance: Request permission via UNUserNotificationCenter.current().requestAuthorization(options: [.alert, .sound, .badge]), then call UIApplication.shared.registerForRemoteNotifications() to get the APNs device token. In AppDelegate, implement didRegisterForRemoteNotificationsWithDeviceToken to capture and send the token to your backend. Set UNUserNotificationCenter.current().delegate in AppDelegate to intercept notifications. Handle received notifications in userNotificationCenter(_:willPresent:withCompletionHandler:), which lets you display alerts even when the app is active.
• What is Xcode Cloud and how does it improve CI/CD for iOS?
• Describe the App Store review process and common rejection reasons.

  Interviewer Insight: App Store questions test operational maturity—interviewers want to know if you've handled a real rejection and what you learned. Strong candidates discuss specific rejections: 'Our v1.0 was rejected for missing privacy policy—we didn't realise iOS required explicit GDPR compliance. Now I audit every release.' Weak answers treat App Store as a black box: 'Uh, you just submit and hope it works.'
• How do you implement certificate pinning in URLSession?

  Sample Answer Guidance: Implement URLSessionDelegate and override urlSession(_:didReceive:completionHandler:) to validate the server's certificate against a pinned public key stored in your bundle. Extract the certificate from the challenge, compare its public key using SecCertificateCopyKey(), and call completionHandler(.useCredential:) or (.cancelAuthenticationChallenge:). Alternatively, use Alamofire's ServerTrustManager for simpler configuration. Trade-off: pinning increases security against MITM attacks but requires careful certificate rotation planning to avoid invalidating app pins.

How Interviewers Evaluate iOS Developer Candidates