400 iOS Interview Questions with Answers 2026

System Architecture & Design Patterns: MVVM, VIPER, TCA, SOLID, and Dependency Injection.

UI Development & Framework Deep-Dives: SwiftUI lifecycle, @Observable, UIKit rendering pipeline, and Auto Layout.

Concurrency & Performance: async/await, Actors, GCD, Race conditions, and Instruments.

Networking, Security & CI/CD: Keychain, SSL Pinning, OAuth, Fastlane, and Unit/UI Testing.

B. It allows the class to be inherited only within the same module.

C. It enables Static Dispatch (Direct Dispatch), potentially improving performance.

D. It requires the use of the @objc attribute for all methods.

E. It ensures the class is stored on the Stack instead of the Heap.

F. It automatically makes all properties immutable.

Correct Answer: C

Overall Explanation: The final keyword prevents a class from being subclassed. Because the compiler knows no other class can override its methods, it can bypass the "vtable" (virtual table) lookup.

Detailed Explanations:

B (Incorrect): This describes public or internal access levels, not final.

C (Correct): By eliminating the need for a lookup table, the compiler uses Static Dispatch.

D (Incorrect): @objc is for Objective-C interoperability, not related to the final restriction.

E (Incorrect): Classes are reference types and remain on the Heap; final doesn't change memory location.

F (Incorrect): final affects inheritance, not the mutability of internal properties.

Question 2: In SwiftUI, what is the primary difference between @StateObject and @ObservedObject?

B. @ObservedObject manages the lifecycle and prevents the object from being destroyed on view redraw.

C. @StateObject ensures the object is only created once, even if the view re-renders.

D. @ObservedObject is required for any class using the @Observable macro.

E. There is no difference; they are interchangeable in iOS 17+.

F. @StateObject can only be used in the App struct.

Correct Answer: C

Overall Explanation: Lifecycle management is the key. @StateObject "owns" the data, while @ObservedObject is for data passed in from outside.

Detailed Explanations:

B (Incorrect): This is the definition of @StateObject, not @ObservedObject.

C (Correct): SwiftUI preserves a @StateObject instance even when the parent view is re-instantiated.

D (Incorrect): The @Observable macro (iOS 17) uses @Bindable or simple properties, not these property wrappers.

E (Incorrect): They have distinct behaviors regarding memory and view refreshes.

F (Incorrect): @StateObject can be used in any SwiftUI view.

Question 3: In Swift Concurrency, how does an Actor prevent data races?

B. By using a private Dispatch Group for every property access.

C. By ensuring only one task can access its mutable state at a time through "Actor Isolation."

D. By converting all reference types to value types during execution.

E. By throwing a compile-time error if any variable is marked var.

F. By forcing the use of lock() and unlock() in every function.

Correct Answer: C

Overall Explanation: Actors provide a synchronization mechanism that serializes access to their internal state, preventing multiple threads from corrupting data simultaneously.

Detailed Explanations:

B (Incorrect): Actors use a cooperative thread pool, not manual Dispatch Groups.

C (Correct): This is the core definition of Actor Isolation.

D (Incorrect): Actors handle reference types; they don't change the underlying type.

E (Incorrect): Actors can have var properties; they just control access to them.

F (Incorrect): The synchronization is handled by the Swift runtime, not manual locking.

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