🚀 iOS Interview Questions and Answers

Your Ultimate Cheat Sheet for iOS Developer Interviews

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👨‍💻 Prepared and Maintained by Keshu Rai a.k.a RaiTech Labs

iOS & Android Expert | Educator | Mentor | Creator @ RaiTech Labs

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📌 About Me

Hi, I’m Keshu Rai, a passionate mobile developer. With over 8 years of industry experience and a growing presence as a mentor and educator, I’ve helped countless developers transition into successful iOS careers.

I’m also the creator of RaiTech Labs — a YouTube channel where I publish high-quality tutorials, course content, and interview prep guides focused on Swift, SwiftUI, and Android development. My goal is to simplify complex concepts and make learning accessible for everyone, whether you're a beginner or looking to land your next senior iOS role.

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📘 Swift Language – iOS Interview Questions (Structured)

• What are the key features of the Swift language?

• What is a type-safe language and how does Swift enforce it?

• What is type inference in Swift?

• What is null safety in Swift and how are Optionals used to achieve it?

• What are Optionals in Swift and why are they important?

• What is the difference between Optional Binding and Optional Chaining?

• What makes Enumerations powerful in Swift?

• What is the difference between let and var in Swift?

• Can a let constant reference a mutable object?

• What happens when you declare a reference type using let?

• How do you create read-only properties in Swift?

• What is the difference between using let and a computed property with only a get?

• How do you make a property read-only outside the class but writable inside it?

• How does Swift support both value and reference types?

• What is the difference between a value type and a reference type?

• What is the difference between a class and a struct in Swift?

• What are the practical use cases where a struct is preferred over a class?

• Why does SwiftUI use structs for defining views?

• How is memory management handled in Swift?

• How is memory management different for classes and structs?

• What is Copy-on-Write in Swift?

• How do Array, Dictionary, and String implement Copy-on-Write in Swift?

• What is protocol-oriented programming and how is it different from object-oriented programming?

• How do Generics work in Swift and why are they useful?

• What are collection types in Swift?

• What are the types of access control modifiers available in Swift?

• Which access modifier is the default in Swift?

• What is the difference between open and public access modifiers?

• What is the difference between private and fileprivate in Swift?

• How does the private(set) access modifier help in encapsulating data while allowing read-only access?

• What are the key differences between stored properties and computed properties in Swift?

• What is the purpose of the lazy keyword in Swift, and in which scenarios is it best used?

• How does the inout keyword enable pass-by-reference behavior in Swift functions?

• What is the role of the defer keyword in Swift, and how is it typically used for resource management?

• How is operator overloading implemented in Swift, and how does it contribute to expressive code?

• What is the process to create a custom operator in Swift, and how do operator types like infix, prefix, and postfix affect its usage?

• How do extensions enhance the functionality of existing types in Swift, and what limitations exist when using them?

• Why are stored properties not allowed inside Swift extensions?

• Why can’t you override methods inside an extension even if the class is subclassed?

• How does Swift promote protocol-oriented programming and what benefits does it offer over traditional object-oriented programming?

• What makes protocol extensions in Swift a powerful tool for writing reusable and modular code?

• How do associated types enable protocols to remain generic while being strongly typed in Swift?

• How does conditional conformance allow Swift types to adopt a protocol only under specific conditions?

• How do generics in Swift contribute to type-safe and reusable code across different data types?

• What are some real-world scenarios where using generics in Swift significantly improves code reusability and maintainability?

• What is a subscript in Swift and how can you create a custom subscript in your type?

• What is Codable in Swift and how does it relate to Encodable and Decodable?

• Is Codable a class, struct, or protocol? How is it used in practice?

• How do enumerations work in Swift, and what are associated values in enums?

• How can you use associated values in enums to represent complex state?

• What is the Result type in Swift, and how does it use associated values to represent success or failure?

• What are the different types of initializers in Swift?

• What is a convenience initializer, and what conditions must be met to use one?

• What is a failable initializer in Swift, and when should you use it?

• What are higher-order functions in Swift and how do they enable functional programming?

• How does the map function work in Swift collections?

• What is the purpose of compactMap, and how does it differ from map?

• How is flatMap used in Swift, and what makes it different from map and compactMap?

• What is the difference between map, compactMap, and flatMap in Swift?

• How does the sort function work in Swift, and how can you use custom sorting logic?

• What is the reduce function in Swift and how can it be used to combine elements of a collection?

• What are the main collection types in Swift, and how do they differ?

• How is an Array different from a Set in Swift?

• Why does Set in Swift only store unique values?

• What are the key features and use-cases for Dictionary in Swift?

• What is the role of the Hashable protocol in Swift, and when should a type conform to it?

• How does Equatable enable comparison of values in Swift?

• What is the Comparable protocol and how does it help in sorting custom types?

• What are the differences between closures and delegates in Swift, and when should each be used?

• What are Property Wrappers in Swift?

• What are Opaque Types in Swift?

• What are some common keywords in Swift?

• 🧩 Design Patterns in Swift

• What is Singleton pattern in Swift?

• Why should Singleton be avoided?

• When should Singleton be used?

• What is Observer pattern in Swift?

• What is Delegate pattern in Swift?

• What is Façade pattern in Swift?

• What is Decorator pattern in Swift?

• What is Adapter pattern in Swift?

• What is Memento pattern in Swift?

• What is Strategy pattern in Swift?

• What is Factory Method pattern in Swift?

• What is Abstract Factory pattern in Swift?

• What is Builder pattern in Swift?

• What is Proxy pattern in Swift?

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🧱 SOLID Principles in Swift

• What is the Single Responsibility Principle?
• What is the Open/Closed Principle?
• What is the Liskov Substitution Principle?
• What is the Interface Segregation Principle?
• What is the Dependency Inversion Principle?

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💉 Dependency Injection in Swift

• What is Dependency Injection?
• What are the types of Dependency Injection?
• Why use Dependency Injection?
• What is Resolver?
• What is SwiftInject?

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🧬 Core Swift Concepts

• What is Composition over Inheritance?
• What is a Pure Function?

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🗃️ Local Data Storage

• What is Core Data?
• What is Realm?
• What is SQLite?
• What are migrations in Core Data?
• How to insert data using background queue in Core Data?
• What is the difference between Core Data and SQLite?
• Is Core Data encrypted?
• What are the delete rules in Core Data?
• What is No Action delete rule?
• What is Nullify delete rule?
• What is Cascade delete rule?
• What is Deny delete rule?
• What are the types of persistent store in Core Data?
• What is XML store type?
• What is Binary store type?
• What is SQLite store type?
• What is In-Memory store type?
• What are the concurrency types in Core Data?
• What is NSMainQueueConcurrencyType?
• What is NSPrivateQueueConcurrencyType?
• How to pass Managed Object between contexts on different queues?
• What are performance guidelines for Core Data?

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🧬 App Lifecycle

• What is the lifecycle of AppDelegate and SceneDelegate?
• What is the lifecycle of UIViewController?
• What is the lifecycle of UIView?

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🌐 REST API Integration

• What is URLSession in Swift?
• What is URLRequest in Swift?
• What is URLComponents in Swift?
• What are the different HTTP methods?
• What are HTTP response status codes?
• What is OAuth protocol?
• What is caching in iOS apps?
• What is Result type in Swift?
• How do you handle retry calls in API requests?
• How do you check for internet availability in iOS?

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⚙️ GCD and OperationQueue

• What is the difference between GCD and OperationQueue?
• What are the different types of queues in GCD?
• What is the difference between Serial and Concurrent queues?
• What is Quality of Service (QoS) in GCD?
• What is DispatchWorkItem in GCD?
• What is DispatchGroup in GCD?
• What is BlockOperation in OperationQueue?

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🏗️ Architecture Patterns

• What is the MVC architecture pattern in iOS?
• What is the MVVM architecture pattern in iOS?
• What is MVVM-C architecture pattern in iOS?
• What is VIPER/VIP architecture pattern in iOS?
• Which architecture pattern is the best for iOS and why?
• How do you choose an architecture for a project?
• What is Modular Architecture in iOS?
• What is TCA architecture in iOS?
• What is VIPER/VIP and its components?
• How can architecture patterns be used with SOLID principles and dependency injection?

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🧠 Memory Management

• What are Strong, Weak, and Unowned references in Swift?
• When should you use Weak and Unowned references in Swift?
• What are the common ways to prevent memory leaks during development?
• How is the deinit method used in Swift?
• How can you find memory leaks, memory allocations, and retain cycles?

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🧑‍💻 Git

• What Git flow have you used in past projects?
• What is the difference between merge and rebase in Git?
• How do you reset the last commit in Git? How can you change the last commit message?
• What is the cherry-pick command in Git used for?
• What is the difference between a hard reset and a soft reset in Git?
• What is Git stash, and how is it used?

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🏃‍♂️ Agile Process

• What Agile process do you follow in your projects?
• How do you plan sprints in Agile?
• How do you estimate stories in Agile?
• What is backlog refinement in Agile?
• What is a Sprint retrospective, and why is it important?
• What is a Sprint review or showcase, and how is it conducted?

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📈 Code Quality Practices

• What code quality checks do you use during the PR process? (e.g., SonarQube, quality gate, unit test coverage, peer code review)
• What are the code review practices or guidelines followed to maintain code quality?

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🔐 Security Mechanisms

• What are the security mechanisms used to make an app secure?
• What is SSL pinning? What is the difference between certificate pinning and public key pinning?
• How can you ensure that SSL pinning is perfectly integrated in an app?
• How do you securely store data in an app? What is the Keychain storage used for?
• How do you implement encryption on the database in an app?
• What are the different encryption algorithms used in app security (e.g., AES, RSA, SHA)?
• How do you check for jailbroken devices?
• What is App Transport Security (ATS), and how does it contribute to app security?
• How can you prevent screenshot capturing within an app?
• How can you avoid exposing confidential information, such as API keys, in a code repository?
• What are the best practices for managing debug logs in production apps?

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🛠️ Managing Different Environments

• How do you manage different environments such as DEV, SIT, UAT, and Production?
• What is the .xcconfig file, and how is it used to manage different environments in an app?
• What is the difference between a Scheme and a Target in Xcode?

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⚙️ Dispatch and Swift Performance

• What is dynamic dispatch, and how does it differ from static dispatch?
• What is the final keyword in Swift? How does it help improve Swift code performance?
• What are the best practices for writing high-performance Swift code?
• What is the difference between setNeedsLayout(), layoutIfNeeded(), and layoutSubviews() in Auto Layout?

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📐 Auto Layout

• What is Content Hugging Priority and Compression Resistance Priority in Auto Layout?

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🚀 Package Managers

• What are CocoaPods, Swift Package Manager (SPM), and Carthage? What are the differences between them?

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🔔 Push Notifications

• What is the difference between Apple Push Notification Authentication Key (.p8) and Apple Push Notification service SSL certificate (.p12)?

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📱 App Store Mechanism

• What are the different types of provisioning profiles used in iOS development?
• What are the different certificate types used in iOS development?
• How does TestFlight beta testing work, and what is the difference between internal and external testing?

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🧪 Unit Testing with XCTest

• How do you use the XCTest framework for Unit Testing in Swift?
• How do you manage real and mock implementations in API testing?
• What are the different types of assertions used in Unit Testing?
• What is XCTSkipUnless used for in Unit Testing?
• How does Dependency Injection help with Unit Testing?
• How do you test asynchronous tasks or real API integration in Swift?
• What is the use case of tearDown() and setup() methods in testing?
• What is behavior-driven testing, and how do you write behavior-driven tests in iOS?
• What is the Quick and Nimble framework, and how is it used for Unit Testing?
• Is setUpWithError() called before each test or only before the first test?
• Is tearDownWithError() called after each test?
• What is SnapshotTesting, and which framework is used for it?
• What is code coverage in testing?

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🌀 Functional Reactive Programming – Combine

• What are Publishers and Subscribers in Combine?
• What are the subjects in Combine? How do PassThroughSubject and CurrentValueSubject work?
• What are transforming operators in Combine, and how do they work?
  • How does collect work in Combine?
  • How does map work in Combine?
  • How does flatMap work in Combine?
  • How does scan work in Combine?
• What are filtering operators in Combine, and how do they work?
  • How does filter work in Combine?
  • How does removeDuplicates work in Combine?
  • How does compactMap work in Combine?
  • How does ignoreOutput work in Combine?
  • How do first and last work in Combine?
  • How do dropFirst and drop work in Combine?
  • How does prefix work in Combine?
• What are combining operators in Combine, and how do they work?
  • How does prepend work in Combine?
  • How does append work in Combine?
  • How does switchToLatest work in Combine?
  • How does merge work in Combine?
  • How does combineLatest work in Combine?
  • How does zip work in Combine?
• What are time manipulation operators in Combine, and how do they work?
  • How does debounce work in Combine?
  • How does throttle work in Combine?
  • How does timeout work in Combine?
• How do you debug Combine pipelines?
• How do share and multicast operators work in Combine?
• What is Future in Combine, and how is it used?
• What is backpressure in Combine, and how can it be achieved?
• What is AnyCancellable in Combine, and how is it used?

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🖥️ SwiftUI

• What is the difference between @State and @StateObject in SwiftUI?
• What is @ObservedObject and when should it be used in SwiftUI?
• What is @Published and how does it work in SwiftUI?
• What is @Environment in SwiftUI, and when should it be used?
• What is @EnvironmentObject in SwiftUI, and how does it work?
• What is @AppStorage in SwiftUI, and how is it useful?
• What is @Binding in SwiftUI, and when should it be used?
• If a struct contains a @Binding property, how do you create a custom initializer for that struct?
• What is @FocusedBinding in SwiftUI, and how is it different from @Binding?
• What is @GestureState in SwiftUI, and how does it work?
• What is @UIApplicationDelegateAdaptor in SwiftUI, and how is it used?
• What are view modifiers in SwiftUI, and how are they applied to views?
• What is the purpose of the some keyword in SwiftUI?
• How do you create custom view modifiers in SwiftUI?
• How do you navigate between views in SwiftUI?
• How do you interact with UIKit components in SwiftUI using UIViewControllerRepresentable and UIViewRepresentable?
• What is AnyView in SwiftUI, and when should it be used?
• How can you avoid using AnyView in SwiftUI, and what is the benefit of using @ViewBuilder?
• What is @ViewBuilder, and how is it used to build views in SwiftUI?

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🛠️ Fastlane

• What are the different methods available for authenticating with Apple services using Fastlane?
• What are the roles of AppFile and FastFile in Fastlane configuration?
• What is Fastlane match, and how is it useful for managing certificates and provisioning profiles?
• What are the different types of lanes available in Fastlane?

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🚀 New Features in Swift

• What is structured concurrency in Swift, and how does it improve async tasks?
• What are async/await, and how do they simplify asynchronous programming in Swift?
• What is AsyncSequence, and how is it used in Swift for handling sequences of asynchronous events?
• What are effectful read-only properties, asynchronous properties, and throwing properties in Swift?
• What are Task and TaskGroup in Swift, and how are they used for concurrent programming?
• What are Actor and GlobalActor, and how do they help manage concurrency and data safety in Swift?
• What is the purpose of the @Sendable attribute, and how does it relate to the Sendable protocol in Swift?

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