65 iOS Interview Questions and Answers PDF 2025

iOS Developer Interview Questions PDF

An iOS developer is a software engineer who specializes in building applications for Apple’s iOS platform, which powers devices like iPhones, iPads, and iPods. Their job involves designing, coding, testing, and maintaining mobile apps using languages such as Swift and Objective-C, and frameworks like UIKit, SwiftUI, and CoreData.

Current demand for skilled iOS developers is at an all-time high. Top tech companies, startups, and even enterprises rely on iOS developers to create engaging and innovative apps for their users. Their work directly impacts user experience, business growth, and brand reputation, making their role extremely valuable in the software industry.

Because of this high demand and the competitive nature of iOS development roles, preparing thoroughly for interviews is essential. Interviews often test your grasp of Swift programming, app architecture, memory management, and debugging techniques.

In this article, we have compiled a comprehensive list of iOS interview questions and answers for both freshers and experienced professionals, along with specialized questions for Swift iOS development.

iOS Developer Interview Questions and Answers for Freshers

Que 1. What are the differences between let and var in Swift?

Answer: let is used to declare constants whose value cannot be changed once assigned, while var is used to declare variables that can be modified. Example:

let name = "John"  // constant
var age = 25       // variable
age = 26           // allowed

Que 2. What is ARC (Automatic Reference Counting) in iOS?

Answer: ARC is a memory management mechanism in iOS that automatically keeps track of object references and deallocates memory when objects are no longer in use, helping to prevent memory leaks.

Que 3. What is the difference between a struct and a class in Swift?

Answer:

  • struct is a value type (copied when assigned).
  • class is a reference type (shared reference when assigned).
  • Classes support inheritance, structs do not.

Que 4. Explain the difference between frame and bounds in UIKit.

Answer: frame defines the view’s position and size in its superview’s coordinate system, while bounds defines the view’s own coordinate system, typically starting at (0,0).

Que 5. What is the difference between synchronous and asynchronous tasks in iOS?

Answer:

  • Synchronous: Tasks execute one after another, blocking the thread until completion.
  • Asynchronous: Tasks run independently, allowing the thread to continue without waiting.

Que 6. What is the difference between delegates and notifications?

Answer: Delegates establish a one-to-one communication pattern, while notifications support one-to-many communication. Delegates are more suitable when one object needs updates from another object.

Que 7. What is the use of DispatchQueue in iOS?

Answer: DispatchQueue is part of GCD (Grand Central Dispatch) and is used for managing tasks concurrently or serially. Example:

DispatchQueue.global().async {
    // background task
}

Que 8. What is the difference between weak and unowned references?

Answer:

  • weak: References that do not keep a strong hold on the object and can become nil when the object is deallocated.
  • unowned: Similar but assumes the reference will never be nil. Accessing it after deallocation will cause a crash.

Que 9. What is the difference between storyboard and XIB?

Answer:

  • Storyboard: Contains multiple screens and navigation flows in one file.
  • XIB: Represents a single view or screen.
    Storyboards simplify navigation, while XIBs are modular and can be reused.

Que 10. Explain MVC architecture in iOS.

Answer: MVC (Model-View-Controller) separates concerns:

  • Model: Handles data and business logic.
  • View: Displays UI elements.
  • Controller: Connects model and view, handles user interactions.

Que 11. What is the difference between URLSession and NSURLConnection?

Answer: URLSession is the modern, more flexible, and efficient API for networking tasks, while NSURLConnection is deprecated and less efficient.

Que 12. Explain the use of optional in Swift.

Answer: Optionals allow variables to store either a value or nil. Declared using ?. Example:

var name: String? = nil
name = "John"

Que 13. What are background modes in iOS?

Answer: Background modes allow apps to continue specific tasks when they are not in the foreground. Examples include background audio, location updates, and VOIP.

Que 14. What is the difference between shallow copy and deep copy?

Answer:

  • Shallow copy: Copies only the reference to the data.
  • Deep copy: Copies the data itself, creating a completely independent object.

Que 15. What are closures in Swift?

Answer: Closures are self-contained blocks of functionality that can be passed around in code, similar to lambdas in other languages. Example:

let greet = { (name: String) -> String in
    return "Hello \(name)"
}

Que 16. What is the difference between @escaping and non-escaping closures?

Answer:

  • Non-escaping: Closure is executed before the function returns.
  • Escaping: Closure is stored and can be executed after the function returns, marked using @escaping.

Que 17. Explain the difference between AppDelegate and SceneDelegate.

Answer:

  • AppDelegate: Handles app-level events (launch, background, termination).
  • SceneDelegate: Introduced in iOS 13, handles multiple windows or scenes within the app.

Que 18. Explain the difference between synchronous and asynchronous network calls with an example.

Answer:

  • Synchronous: Blocks execution until the task finishes.
  • Asynchronous: Allows other tasks to continue.
    Example (asynchronous):
URLSession.shared.dataTask(with: url) { data, response, error in
    // Handle data
}.resume()

Que 19. What is the difference between main thread and background threads?

Answer:

  • Main thread: Handles UI updates, user interactions.
  • Background threads: Used for heavy tasks like network calls or database operations to avoid blocking UI.

Que 20. Provide a table showing the difference between UITableView and UICollectionView.

Answer:

FeatureUITableViewUICollectionView
LayoutSingle-column listGrid or custom layouts
Cell ReusabilityYesYes
Section HeadersSupportedSupported
FlexibilityLess flexibleHighly customizable

iOS Developer Interview Questions Freshers

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IOS Interview Questions and Answers for Experienced

Que 21. What are the differences between strong, weak, and unowned references in Swift?

Answer:

  • Strong: Retains a strong hold on the object; the default reference type.
  • Weak: Does not retain the object and can become nil when the object is deallocated.
  • Unowned: Similar to weak but cannot be nil; accessing after deallocation causes a crash.
    Example:
class A { var b: B? }
class B { weak var a: A? } // prevents retain cycle

Que 22. What is the difference between OperationQueue and DispatchQueue?

Answer:

  • DispatchQueue (GCD): Lightweight, low-level API for concurrency.
  • OperationQueue: Built on top of GCD, allows task dependencies, priorities, and cancellation.

Que 23. How do you avoid retain cycles in closures?

Answer: By using [weak self] or [unowned self] in the closure capture list:

myClosure = { [weak self] in
    self?.doSomething()
}

Que 24. What are the advantages of using Codable protocol in Swift?

Answer:

  • Automatically encodes/decodes structs or classes to/from JSON or Property Lists.
  • Reduces boilerplate code compared to NSCoding.
    Example:
struct User: Codable { var name: String; var age: Int }

Que 25. Explain dependency injection and how you implement it in iOS.

Answer: Dependency Injection (DI) is the process of providing dependencies to an object externally rather than creating them inside.

  • Constructor Injection: Dependencies passed in initializer.
  • Property Injection: Dependencies assigned to properties.
    DI frameworks like Swinject are used for large projects.

Que 26. How do you handle large data sets in UITableView or UICollectionView?

Answer:

  • Use cell reuse identifiers.
  • Load data in chunks using pagination.
  • Cache data and images.
  • Use DiffableDataSource (iOS 13+) for better performance and updates.

Que 27. What are associated objects in Objective-C/Swift?

Answer: Associated objects allow developers to add properties to existing classes at runtime using objc_setAssociatedObject and objc_getAssociatedObject.

Que 28. How would you implement thread safety in Swift?

Answer:

  • Use serial queues to synchronize access.
  • Use NSLock or DispatchSemaphore.
  • Use DispatchQueue.sync to perform atomic operations.
    Example:
let lock = NSLock()
lock.lock()
// critical section
lock.unlock()

Que 29. Explain the differences between synchronous, asynchronous, and concurrent tasks.

Answer:

  • Synchronous: Waits for task completion.
  • Asynchronous: Does not block the thread.
  • Concurrent: Multiple tasks execute at the same time.
    Asynchronous + concurrent leads to maximum parallelism.

Que 30. How would you optimize the launch time of an iOS app?

Answer:

  • Defer heavy tasks to background after launch.
  • Reduce the number of dynamic frameworks.
  • Avoid unnecessary work in AppDelegate.
  • Pre-load resources asynchronously.

Que 31. What is the difference between NSCache and using a dictionary for caching?

Answer:

  • NSCache: Automatically removes objects when memory is low, thread-safe, and allows object cost/priority.
  • Dictionary: Manual memory management, not thread-safe.

Que 32. What is the difference between keychain and user defaults for storing data?

Answer:

  • Keychain: Secure storage for sensitive data like tokens and passwords (encrypted).
  • UserDefaults: Stores non-sensitive user preferences and settings.

Que 33. Explain the difference between value types and reference types in Swift with performance implications.

Answer:

  • Value types (structs, enums): Copied on assignment; faster and safer in multi-threading.
  • Reference types (classes): Shared reference; requires careful memory management.

Que 34. How do you debug memory leaks in iOS?

Answer:

  • Use Instruments – Leaks and Allocations.
  • Use Xcode’s memory graph debugger.
  • Look for retain cycles and unbalanced retain/release operations.

Que 35. What is the difference between REST and GraphQL in iOS APIs?

Answer:

  • REST: Fixed endpoints, often over-fetch or under-fetch data.
  • GraphQL: Single endpoint, fetch exactly what you need.
    GraphQL requires a schema and can reduce network calls in mobile apps.

Que 36. How do you handle background tasks in iOS?

Answer:

  • Use Background Fetch for periodic updates.
  • Use URLSession background tasks for uploads/downloads.
  • Use BGTaskScheduler (iOS 13+) for long-running tasks.

Que 37. What is the difference between KVO (Key-Value Observing) and Combine framework?

Answer:

  • KVO: Legacy API, verbose and error-prone.
  • Combine: Modern reactive framework, type-safe and integrates seamlessly with Swift.

Que 38. Explain the difference between synchronous and asynchronous Core Data saving.

Answer:

  • Synchronous (performAndWait): Blocks the current thread until the save is complete.
  • Asynchronous (perform): Saves in the background and returns immediately.

Que 39. How do you implement a custom transition animation in iOS?

Answer: Implement UIViewControllerTransitioningDelegate and UIViewControllerAnimatedTransitioning protocols to define custom animations during view controller presentation and dismissal.

Que 40. Provide a table comparing Objective-C and Swift.

Answer:

FeatureObjective-CSwift
SyntaxVerbose, uses header and impl filesConcise, single file
Type SafetyWeakStrong
Memory ManagementManual + ARCARC by default
InteroperabilityHigh with C/C++Works with Objective-C via bridging

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IOS Interview Questions and Answers for Senior Developer

Que 41. How do you structure a large-scale iOS application to ensure maintainability?

Answer: Use modular architectures like MVVM, VIPER, or Clean Architecture. Break the app into independent modules or frameworks, apply dependency injection, and separate business logic from UI. This allows better testing, scalability, and code reuse.

Que 42. How would you handle complex state management in an iOS application?

Answer: Combine frameworks like Combine, Swift Concurrency, or external libraries like RxSwift with a unidirectional data flow architecture such as Redux/ReSwift. This ensures predictable state updates and prevents race conditions.

Que 43. How do you design a secure authentication flow for iOS?

Answer:

  • Use Keychain for token storage.
  • Implement biometric authentication via FaceID/TouchID.
  • Use OAuth 2.0 / OpenID Connect with refresh tokens.
  • Ensure secure networking using ATS, SSL pinning, and encrypted tokens.

Que 44. How do you handle and optimize offline data synchronization?

Answer: Use Core Data or Realm for local storage, track pending changes with a queue, and sync via background tasks or BGTaskScheduler. Conflict resolution strategies include last-write-wins, versioning, or merge policies.

Que 45. Explain the difference between structured concurrency (Swift 5.5) and GCD.

Answer:

  • Structured Concurrency: Uses async/await and Task hierarchy for clearer cancellation and error propagation.
  • GCD: Lower-level queue management without built-in task relationships.
    Structured concurrency simplifies complex async code and debugging.

Que 46. How do you handle push notifications for multiple user environments (staging, production)?

Answer:

  • Configure separate APNs certificates/keys for each environment.
  • Use environment-specific endpoints.
  • Implement push token segregation at the backend to prevent cross-environment message delivery.

Que 47. How do you detect and fix performance bottlenecks in iOS apps?

Answer:

  • Use Instruments (Time Profiler, Allocations, Energy Log).
  • Monitor Main Thread Checker for UI blocks.
  • Reduce overdraw using Core Animation tools.
  • Profile network requests and cache heavy data.

Que 48. How do you manage modularization and shared code across multiple iOS apps?

Answer: Create internal Swift packages or private CocoaPods frameworks for shared components. Use XCFrameworks for compiled libraries. Maintain separate repositories with versioning for better dependency management.

Que 49. How would you design a scalable REST/GraphQL layer in iOS?

Answer:

  • Abstract API calls using a network layer with protocol-based design.
  • Implement decoders, error handling, and caching in one place.
  • For GraphQL, use Apollo iOS with automatic code generation.
  • Apply Combine/async-await for request handling.

Que 50. How would you handle advanced security features like SSL Pinning?

Answer: Implement URLSessionDelegate and validate the server certificate or public key during SSL handshake. Example:

func urlSession(_ session: URLSession, didReceive challenge: URLAuthenticationChallenge, completionHandler: ...) {
   // Compare certificate with stored hash
}

Que 51. How do you implement custom instrumentation and analytics at scale?

Answer:

  • Use an event bus for analytics events.
  • Implement batching to reduce network overhead.
  • Leverage OSLog for structured logs.
  • Ensure privacy compliance (GDPR/CCPA).

Que 52. Explain how to design background tasks for critical business workflows.

Answer:

  • Use BGProcessingTaskRequest for long tasks (iOS 13+).
  • Schedule URLSession background tasks for uploads/downloads.
  • Always provide fallback mechanisms for failed background execution and store state persistently.

Que 53. How would you handle concurrency issues in Core Data at scale?

Answer:

  • Use separate contexts per thread.
  • Merge changes via NSPersistentContainer.viewContext.automaticallyMergesChangesFromParent = true.
  • Use perform/performAndWait for context operations..

Que 54. How do you plan for multi-platform apps (iOS, macOS, watchOS, tvOS) in the same codebase?

Answer:

  • Share core logic in Swift Packages.
  • Use #if os(iOS) conditions for platform-specific code.
  • Adopt SwiftUI for unified UI across platforms.

Que 55. Provide a table comparing VIPER vs Clean Architecture for iOS.

Answer:

AspectVIPERClean Architecture
LayersView, Interactor, Presenter, Entity, RouterEntities, Use Cases, Interface Adapters, UI
Dependency FlowUnidirectionalUnidirectional
BoilerplateHighMedium
TestingVery testableVery testable
Learning CurveSteeperModerate

iOS Interview Questions Answers

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Swift IOS Interview Questions and Answers

Que 56. What is the difference between struct and class in Swift?

Answer:

  • Struct: Value type, copied on assignment, cannot inherit other structs, faster in memory operations.
  • Class: Reference type, passed by reference, supports inheritance and deinitializers.
    Example:
struct Person { var name: String }
class Employee { var name: String = "" }

Que 57. What are property observers in Swift?

Answer: Property observers monitor and respond to property value changes using willSet and didSet.

var age: Int = 0 {
   willSet { print("Will set age to \(newValue)") }
   didSet { print("Age changed from \(oldValue) to \(age)") }
}

Que 58. What is the difference between map, flatMap, and compactMap?

Answer:

  • map: Transforms elements and returns optional if original array has optional.
  • flatMap: Flattens nested collections into a single collection.
  • compactMap: Removes nil values after transforming.

Example:

let numbers = ["1","2","a"]
let mapped = numbers.map { Int($0) }        // [Optional(1), Optional(2), nil]
let compact = numbers.compactMap { Int($0)} // [1,2]

Que 59. What is the difference between escaping and non-escaping closures?

Answer:

  • Non-escaping: Closure is executed before the function returns.
  • Escaping: Closure can be called after the function returns and must be marked with @escaping.
    Example:
func fetchData(completion: @escaping () -> Void) { ... }

Que 60. How does Swift handle memory management with ARC?

Answer: Swift uses Automatic Reference Counting (ARC). It tracks strong references to objects and deallocates them when reference count is zero. To avoid retain cycles, developers use weak or unowned references.

Que 61. Explain the difference between Any, AnyObject, and NSObject.

Answer:

  • Any: Represents any type (struct, enum, class, etc.).
  • AnyObject: Represents any class type instance.
  • NSObject: Base class for most Objective-C classes, provides KVO, selectors, etc.

Que 62. What is the difference between lazy stored properties and computed properties?

Answer:

  • Lazy: Value is initialized only when first accessed and stored in memory.
  • Computed: Value is calculated every time it is accessed and doesn’t store a value.
    Example:
lazy var data = fetchData()
var square: Int { return value * value }

Que 63. How do you handle concurrency using async/await in Swift?

Answer: Swift 5.5 introduced structured concurrency:

func fetch() async throws -> Data { ... }
Task {
    let data = try await fetch()
}

This allows easier chaining, error handling, and cancellation compared to GCD.

Que 64. How do you use protocol extensions in Swift effectively?

Answer: Protocol extensions provide default implementations:

protocol Greetable { func greet() }
extension Greetable {
   func greet() { print("Hello") }
}

This reduces code duplication and allows shared behavior among conforming types.

Que 65. Provide a table showing the difference between weak and unowned references.

Answer:

Featureweakunowned
Nil allowedYes (automatically becomes nil)No (crashes if accessed after deallocation)
ARC behaviorDoes not increase reference countDoes not increase reference count
Use caseWhen reference can become nilWhen reference is guaranteed to exist during access

IOS Interview Questions PDF

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FAQs: IOS Interview Questions

What is the role of an iOS Developer?

An iOS Developer is responsible for designing, developing, testing, and maintaining applications for Apple’s iOS platform. They work with Swift or Objective-C, integrate APIs, handle UI/UX elements, and ensure app performance and security on devices like iPhones, iPads, and Apple Watches.

What challenges do iOS Developers face during the job?

iOS Developers often face challenges like handling multiple device screen sizes, optimizing performance, maintaining backward compatibility with older iOS versions, managing memory effectively, and staying updated with Apple’s frequently changing development guidelines and APIs.

What challenges can you expect during an iOS Developer interview?

Interviews usually test problem-solving skills, knowledge of Swift, iOS frameworks, design patterns, and debugging. Candidates may also face algorithm-based coding challenges, architecture design discussions, and questions on topics like concurrency, memory management, and UI performance optimization.

What are the required skills to become a successful iOS Developer?

Strong skills in Swift or Objective-C, UIKit, Core Data, networking (REST/GraphQL), Xcode, and testing frameworks are essential. Knowledge of design patterns (MVC, MVVM, VIPER), Git, continuous integration, and familiarity with Apple’s ecosystem are also highly valuable.

What is the average salary of an iOS Developer in the USA?

The average salary of an iOS Developer in the USA ranges between $95,000 and $140,000 per year, depending on experience, company size, and location. Senior developers or those with expertise in advanced technologies can earn $150,000 or more annually.

Which top companies hire iOS Developers?

Leading companies hiring iOS Developers include Apple, Google, Microsoft, Amazon, Meta (Facebook), and top product-based startups. Many Fortune 500 companies, fintech firms, and software consultancies also consistently hire for this role.

What is the career growth path for iOS Developers?

iOS Developers can grow into roles like Senior iOS Developer, Lead Mobile Engineer, Mobile Architect, or Engineering Manager. They may also branch into cross-platform development, product management, or entrepreneurship in mobile app development.

Conclusion

This iOS developer interview guide helps you prepare for your next job interview with questions for both new and experienced developers. We included special Swift programming questions that iOS developers need to know. The guide covers everything from basic concepts to advanced topics that companies ask about.

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