iOS interview questions and answers

1. Safely unwrapping a Swift optional

name is of type String?. Which is the safest way to use it only when it has a value?

1. A.if let name { print(name) }
2. B.print(name!)
3. C.print(name as String)
4. D.print(String(name))

2. Swift class shared reference

What does this Swift code print?

class Counter { var value = 0 }
let a = Counter()
let b = a
b.value = 3
print(a.value)

1. A.0
2. B.Compile error because b is declared with let
3. C.nil
4. D.3

3. Decoding JSON with extra keys

What does this Swift code print?

struct User: Codable {
  let id: Int
  let name: String
}
let json = #"{"id": 7, "name": "Sara", "age": 30}"#.data(using: .utf8)!
let user = try JSONDecoder().decode(User.self, from: json)
print(user.name)

1. A.A DecodingError, because age is not a property of User
2. B.Sara
3. C.nil
4. D.Optional("Sara")

4. What await means in Swift

What happens at an await when calling an async function in Swift?

1. A.The current thread is blocked until the result arrives, but the system starts a second main thread so the UI keeps responding
2. B.The function may suspend there, freeing the thread for other work, and resumes when the result is ready
3. C.The call runs in a separate process
4. D.The call is skipped when the device is offline

5. iOS build fails after adding a library

After `npm install` of a library with native iOS code, the iOS build fails with a missing module error. What step was likely skipped?

1. A.Restarting the Metro bundler twice
2. B.Running pod install in the ios folder
3. C.Clearing the Android Gradle cache
4. D.Running npm audit fix --force

6. iOS app moved to the background

A user presses the home gesture while your iOS app is open and does not return. With no background mode active, what normally happens soon after?

1. A.The app keeps running all code until the battery is low
2. B.The app is suspended in memory and may later be terminated
3. C.The app is deleted from the phone by the system
4. D.The app restarts automatically every few minutes

7. viewDidLoad or viewWillAppear

A UIKit screen should refresh its unread count every time it comes back on screen, not only the first time. Where does the refresh belong?

1. A.viewDidLoad
2. B.init(coder:)
3. C.deinit
4. D.viewWillAppear

8. Urgent fix waiting in review

A critical bug fix for a payments crash is waiting in App Store review. What can the team request?

1. A.An expedited review, explaining the critical issue
2. B.A refund of the developer fee to skip review
3. C.Direct installation on users' phones by Apple
4. D.Removal of the review step for all future builds

9. What guard let is for

Why is guard let common at the start of functions?

1. A.It unwraps values and exits early if they are nil
2. B.It runs the rest of the function on a background thread
3. C.It repeats the function until a value is not nil
4. D.It turns every optional into a default value

10. Giving an optional a default

What is the value of name when user.nickname is nil?

let name = user.nickname ?? "Guest"

1. A.nil
2. B.An empty string
3. C."Guest"
4. D.It crashes at runtime

11. Force unwrapping nil

What happens when this runs and the text is not a number?

let value = Int(textField.text ?? "")!

1. A.The app crashes with a fatal error
2. B.value is quietly set to 0
3. C.value is quietly set to nil
4. D.The whole line is skipped

12. A switch without default

An enum OrderStatus has cases placed, shipped and delivered. A switch handles only placed and shipped, with no default. What happens?

1. A.delivered silently does nothing at all
2. B.It crashes at runtime when delivered is passed
3. C.delivered falls through into the shipped case
4. D.A compile error: the switch must be exhaustive

13. What try? returns

What is the type of data here?

let data = try? Data(contentsOf: fileURL)

1. A.Data
2. B.Result<Data, Error>
3. C.Data?
4. D.Error?

14. Reading a missing key

prices is [String: Int]. What does prices["mango"] return when the key is missing?

1. A.0, the default value of Int
2. B.It crashes with an index error
3. C.An empty dictionary
4. D.nil, because the subscript returns Int?

15. A computed property

What is true about fullName?

struct Person {
    var first: String
    var last: String
    var fullName: String { "\(first) \(last)" }
}

1. A.It stores the combined name when the struct is created
2. B.It is recomputed from the other properties each time it is read
3. C.It must be declared with let
4. D.It can only be read once

16. Marking UI code with @MainActor

What does annotating a view model class with @MainActor guarantee?

1. A.It runs all its methods on a background thread
2. B.It makes the class a singleton
3. C.Its properties and methods are used on the main thread
4. D.It turns off strict concurrency checks

17. Mapping with a key path

What does users.map(\.name) return?

1. A.An array of each user’s name
2. B.A dictionary keyed by name
3. C.The first user’s name only
4. D.A sorted copy of users

18. Using a SwiftUI view in UIKit

An older UIKit app wants to show a new SwiftUI settings screen. Which type wraps the SwiftUI view as a view controller?

1. A.UIViewRepresentable
2. B.UINavigationBar
3. C.UIStoryboardSegue
4. D.UIHostingController

19. Localising strings in Xcode

Since Xcode 15, what is the recommended file for managing app string translations?

1. A.A plain .txt file per language
2. B.A String Catalog (.xcstrings)
3. C.A JSON file loaded at launch
4. D.Hard-coded strings in each view

20. Previewing a SwiftUI view

What does the #Preview macro do in a SwiftUI file?

1. A.Runs the view on a real device on build
2. B.Generates unit tests for the view
3. C.Declares a live preview shown in Xcode’s canvas
4. D.Ships the view to TestFlight

21. SwiftUI .task when leaving a screen

A SwiftUI view loads data with .task { await vm.load() }. The user navigates away before loading finishes. What happens?

1. A.The task keeps running until the app is terminated, because Swift tasks are never cancelled unless you call cancel() yourself
2. B.SwiftUI cancels the task automatically when the view disappears, so load() should respect cancellation
3. C.The app crashes because the view no longer exists
4. D.The task moves to the next visible view

22. Unreadable iOS crash stack traces

Crashlytics shows iOS crash stack traces for the latest release as raw memory addresses with no function names. What is most likely missing?

1. A.More logging statements in the app
2. B.The crashes come from jailbroken devices, which strip function names from stack traces before sending them to Crashlytics
3. C.Swift support in Crashlytics
4. D.The dSYM files for that build were not uploaded, so the crashes cannot be symbolicated

23. The @Observable macro in SwiftUI

With Swift's @Observable macro (iOS 17+), what decides which views update when a property changes?

1. A.Every view in the app on each property change
2. B.Only views marked with @Published wrappers
3. C.Only views that read that property in their body
4. D.Views refresh on a fixed 60-times-a-second timer

24. Podcast stops when the screen locks

An iOS podcast app stops playing when the user locks the phone. What is missing?

1. A.A Timer that restarts playback every second
2. B.The audio background mode and a playback audio session
3. C.The location permission set to Always
4. D.A silent push notification sent every minute

25. APNs key or certificate

Why do teams prefer an APNs authentication key (.p8) over per-app push certificates?

1. A.A .p8 key lets pushes skip Apple's servers completely
2. B.Certificates cannot send pushes to iPads
3. C.One key works for all the team's apps and does not expire yearly
4. D.A .p8 key makes pushes arrive with higher priority

26. Card number in the app switcher

The iOS app switcher shows a snapshot of your app with the user's card number visible. How do you prevent this?

1. A.Turn off multitasking support for the whole app
2. B.Lower the screen brightness when backgrounded
3. C.Delete the card number from the server
4. D.Cover sensitive views when the scene resigns active

27. TestFlight internal and external testers

A team wants 15 colleagues and 2,000 beta users to try an iOS build. What is the difference between TestFlight internal and external testing?

1. A.External testers need no review; internal builds need full App Review
2. B.Both groups need a full App Store review before every build
3. C.Internal testers need no review; external builds need Beta App Review first
4. D.Internal testing is limited to 2 people and needs a paid account each

28. Upload rejected for the same version

An iOS team uploads version 2.4.0 (build 57), finds a bug, fixes it and uploads again as 2.4.0 (build 57). App Store Connect rejects it. Why?

1. A.The marketing version must change on every single upload
2. B.Each upload for a version needs a higher CFBundleVersion build number
3. C.Builds can only be uploaded once per calendar day
4. D.The bundle identifier must change for every fix

29. Reading an associated value

What does this print?

enum Payment {
    case success(amount: Int)
    case failure(String)
}

let p = Payment.failure("timeout")
switch p {
case .success: print("Success")
case .failure(let reason): print("Failed: \(reason)")
}

1. A.Success
2. B.Failed: timeout
3. C.failure(timeout)
4. D.It does not compile

30. Floating-point money errors

An invoice adds 0.1 + 0.2 for GST calculations and shows 0.30000000000000004. What type is better for money?

1. A.Float, because it uses less memory
2. B.Double with more decimal places
3. C.String, converted when adding
4. D.Decimal, or integers in paise

31. Adding past Int8.max

What happens when this code runs?

var x: Int8 = 127
x += 1

1. A.x silently wraps around to −128
2. B.It traps at runtime with an overflow
3. C.x stays clamped at its max of 127
4. D.x becomes 128, promoted to an Int

32. Getting the first character

Why does name[0] fail to compile for a String?

1. A.Strings are immutable, so indexing is blocked
2. B.Strings use String.Index, because characters vary in size
3. C.Only NSString supports any indexing
4. D.Subscripts need a Character argument

33. Parsing numbers from text

What is the value of result after this runs?

let result = ["1", "x", "3"].compactMap { Int($0) }

1. A.[1, 3]
2. B.[1, nil, 3]
3. C.[1, 0, 3]
4. D.[]

34. Two async let calls

fetchProfile() takes 1 s and fetchOrders() takes 2 s. How long does loadScreen() take?

func loadScreen() async throws -> Screen {
    async let profile = fetchProfile()
    async let orders = fetchOrders()
    return try await Screen(profile: profile, orders: orders)
}

1. A.About 3 s
2. B.About 1 s
3. C.About 2 s
4. D.About 0.5 s

35. Calling into an actor

Code outside the actor reads counter.value. Why does the compiler require await?

1. A.Every property read in Swift needs await
2. B.Actors always run only on the main thread
3. C.Access may wait for the actor to be free
4. D.The value is always fetched from the disk

36. Showing SwiftData results

In SwiftData, what does @Query var notes: [Note] in a view do?

1. A.Fetches notes and refreshes the view on changes
2. B.Fetches once at launch and then never again
3. C.Sends the query off to a remote server
4. D.Creates a separate new database for each view

37. Wrapping a UIKit view in SwiftUI

You wrap a MKMapView with UIViewRepresentable and need its delegate callbacks. Where do they go?

1. A.Directly inside the SwiftUI body
2. B.In a global singleton delegate object
3. C.In the app’s Info.plist configuration
4. D.A Coordinator from makeCoordinator()

38. Saving a draft when the app leaves

You want to save a draft when the app goes to the background. What do you observe in SwiftUI?

1. A.The view’s body being called for the last time
2. B.A timer that runs every second
3. C.@Environment(\.scenePhase) changing to .background
4. D.onDisappear of the root view

39. Swift Testing assertions

In the Swift Testing framework, how do you write a test and check a value?

1. A.Subclass XCTestCase and use print(total)
2. B.Write a main() that returns true or false
3. C.Use assert(total == 400) in production code
4. D.Mark a func with @Test and use #expect(total == 400)

40. Combine sink never fires

A Combine subscription is created with sink in a method, but the closure never runs. What is missing?

1. A.Storing the returned AnyCancellable
2. B.Calling sink twice so it activates
3. C.Marking the method with @MainActor
4. D.Adding receive(on:) after the sink

41. Memory leak with a closure

This view controller is never deallocated after it is dismissed. Why?

class ProfileVC: UIViewController {
  var onUpdate: (() -> Void)?
  override func viewDidLoad() {
    super.viewDidLoad()
    onUpdate = {
      self.reload()
    }
  }
  func reload() {}
}

1. A.viewDidLoad is called twice
2. B.Optionals always leak memory in Swift
3. C.reload is not marked @objc
4. D.The VC strongly holds the closure and the closure strongly captures self, creating a retain cycle; use [weak self]

42. Actor reentrancy in an image cache

Two callers ask this actor for the same URL at the same moment. What happens?

actor ImageCache {
  private var cache: [URL: UIImage] = [:]

  func image(for url: URL) async throws -> UIImage {
    if let cached = cache[url] { return cached }
    let image = try await download(url)
    cache[url] = image
    return image
  }
}

1. A.The actor runs one call at a time from start to finish, so the second caller waits until the first returns and then finds the image already in the cache
2. B.A data race on the dictionary crashes the app
3. C.It does not compile, because actors cannot have async methods
4. D.Both calls may download, because actors are reentrant: while the first call awaits, the second runs and also misses the cache; store in-flight Tasks in the dictionary to share one download

43. Keychain read fails in background

A background refresh task runs while the iPhone is locked, reads the auth token from the Keychain and gets errSecInteractionNotAllowed. What is the cause?

1. A.The Keychain cannot be used by background code at all, so the token should be copied into UserDefaults before the app is suspended so background tasks can read it
2. B.The token was saved with kSecAttrAccessibleWhenUnlocked; items needed in the background should use kSecAttrAccessibleAfterFirstUnlock (the ThisDeviceOnly variant if it should not move to other devices)
3. C.Background tasks have no network access
4. D.The token has expired on the server

44. When a BGAppRefreshTask runs

You submit a BGAppRefreshTaskRequest with earliestBeginDate set to 15 minutes from now. When will the task run?

1. A.Exactly 15 minutes from now
2. B.Every 15 minutes for as long as the app is installed, because a submitted request repeats on that interval until you cancel it with the scheduler
3. C.Immediately, and again after 15 minutes
4. D.No earlier than 15 minutes from now; the system chooses the time based on usage patterns, battery and network, and it may run much later or not at all

45. App killed during a slow launch

An iOS app downloads config synchronously in didFinishLaunching. On slow networks, the system kills it before the first screen appears. Why?

1. A.iOS forbids any network calls during the app launch phase
2. B.A watchdog kills apps that block the main thread at launch
3. C.The app ran out of free disk space for the download
4. D.Synchronous code is not allowed in Swift apps

46. Core Data objects across threads

An iOS app fetches NSManagedObjects on a background context and passes them to the main thread for display. It crashes randomly. What is the rule?

1. A.Managed objects are tied to their context; pass objectIDs instead
2. B.Core Data can only be used from background threads
3. C.Each fetch must create a new persistent store file
4. D.Managed objects must be converted to JSON first

47. Large downloads in Documents on iOS

An iOS app stores 2 GB of re-downloadable videos in the Documents directory. Why might Apple reject it?

1. A.Documents is limited to 100 MB per app
2. B.Videos can only be stored in the Photos library
3. C.Documents is shared with every other app on the phone
4. D.Documents is backed up to iCloud; re-downloadable data must not be

48. Downloads that continue after the app closes

An iOS app downloads 500 MB course videos. Users switch apps and the download stops. Which API lets the system continue the transfer?

1. A.A Timer that restarts the download every 30 seconds
2. B.A background URLSessionConfiguration with a download task
3. C.A default URLSession on a background DispatchQueue
4. D.A silent push notification sent every minute

49. Extension method that is not a requirement

What does this print?

protocol Greeter {}
extension Greeter {
    func hello() -> String { "base" }
}
struct Hindi: Greeter {
    func hello() -> String { "namaste" }
}

let g: any Greeter = Hindi()
print(g.hello())

1. A.namaste
2. B.base
3. C.It does not compile
4. D.base namaste

50. some Shape or any Shape

Which statement about some Shape and any Shape is correct?

1. A.some can hold different types at runtime; any fixes one
2. B.any can hold different conforming types; some fixes one type
3. C.They are identical; any is only newer syntax
4. D.any is only allowed for class protocols

51. Typed throws

With Swift 6 typed throws, what is the type of error in the catch block?

func pay() throws(PaymentError) { /* ... */ }

do {
    try pay()
} catch {
    // error’s type here?
}

1. A.any Error (existential)
2. B.Optional<Error>
3. C.NSError from Foundation
4. D.PaymentError

52. Counting an emoji

What does this print?

let s = "👍🏽"
print(s.count, s.utf16.count)

1. A.2 4
2. B.1 4
3. C.1 2
4. D.4 4

53. Turning a delegate into an AsyncSequence

You want to expose location updates from a delegate-based API as for await. What is the usual tool?

1. A.AsyncStream with a continuation that yields
2. B.A single withCheckedContinuation call
3. C.DispatchGroup with paired enter and leave
4. D.A Timer that fires once every second

54. What the $ prefix gives

For a property declared with a property wrapper, what does the $ prefix (as in $isOn for @State var isOn) access?

1. A.The wrapper’s stored value as an optional
2. B.The memory address of the property
3. C.A copy of the property made at init
4. D.The wrapper’s projectedValue, for @State a Binding

55. Rows showing the wrong data

A List uses ForEach(names, id: \.self). When two people share the name "Priya", editing one row updates the other. Why?

1. A.id: \.self only works for Int arrays
2. B.Duplicate values give two rows the same identity
3. C.List always mixes up rows with strings
4. D.Text views cannot show duplicate strings

56. sync on the main queue

What happens when this code runs on the main thread?

DispatchQueue.main.sync {
    label.text = "Done"
}

1. A.The block runs immediately, then the rest
2. B.The block runs later on a background thread
3. C.It deadlocks; GCD usually traps with a crash
4. D.The block is ignored without any error

57. App rejected for UserDefaults use

App Store Connect flags your app for using UserDefaults and file timestamp APIs without declared reasons. What is required?

1. A.A PrivacyInfo.xcprivacy declaring reasons for those APIs
2. B.Removing every use of UserDefaults from the app
3. C.Asking users for App Tracking Transparency consent
4. D.Adding a privacy policy URL in App Store Connect

58. @State ignores the new value

A view initialises @State from a parameter. The parent later passes a different start value, but the view keeps showing the old one. Why?

struct Stepper: View {
    @State private var count: Int
    init(start: Int) { _count = State(initialValue: start) }
    var body: some View { Text("\(count)") }
}

1. A.Parameters cannot be passed to views with state
2. B.@State is set only when the view’s identity is first created
3. C.The parent must call objectWillChange.send()
4. D.State values reset only on device rotation

59. Which views update with @Observable

A model marked @Observable has name and cartCount. A header view reads only name. When cartCount changes, does the header’s body run again?

1. A.Yes; any change to the model updates every view
2. B.Yes, but only if the view uses @StateObject
3. C.No; views track only the properties they read
4. D.No; @Observable models never update views

60. Search that restarts on new text

A view uses .task(id: query) { await search(query) }. What happens when query changes while a search is running?

1. A.Both searches run and both update the view
2. B.The new query is ignored until the old ends
3. C.The view crashes with a concurrency error
4. D.The running task is cancelled and a new one starts