This iOS Interview Questions and Answers guide helps mobile developers prepare for app development job interviews with the most important questions that companies ask during hiring. We included top iOS questions about Swift programming, app development, and mobile concepts that employers test candidates on.

The guide covers everything from basic iOS fundamentals to advanced app features and development practices that successful developers need to know. Use this guide to practice the most commonly asked iOS questions and increase your chances of getting hired.

Que 1. What is the difference between frame and bounds in iOS?

Answer:

• Frame: The rectangle that defines the view’s location and size in its superview’s coordinate system.

• Bounds: The rectangle that defines the view’s location and size in its own coordinate system. Changing the bounds affects the content drawing area without changing the view’s position in the parent view.

Que 2. What is ARC in iOS?

Answer: ARC (Automatic Reference Counting) is a memory management feature that automatically tracks and releases objects when they are no longer needed. It uses strong, weak, and unowned references to prevent retain cycles.

Que 3. Explain delegation in iOS.

Answer: Delegation is a design pattern where one object assigns responsibility to another object to handle specific tasks or data. It is implemented using a protocol and is commonly used in UIKit for handling events like table view actions.

Que 4. What is the difference between synchronous and asynchronous tasks in iOS?

Answer:

• Synchronous: The task blocks the current thread until it finishes.

• Asynchronous: The task runs in the background, allowing other code to execute simultaneously.

Que 5. What is the purpose of Grand Central Dispatch (GCD)?

Answer: GCD is used for managing concurrent code execution by dispatching tasks to different queues. It helps improve application performance and responsiveness by running tasks asynchronously.

Que 6. What is the difference between strong, weak, and unowned references in Swift?

Answer:

• Strong: Keeps a strong hold on the object, preventing it from being deallocated.

• Weak: Does not retain the object and allows deallocation when no strong references exist.

• Unowned: Similar to weak but assumes the object will not become nil during its lifetime.

Que 7. What is a protocol in Swift?

Answer: A protocol defines a blueprint of methods, properties, and other requirements that a class, struct, or enum can adopt. Protocols support multiple conformances and are used to achieve abstraction.

Que 8. What is the difference between viewDidLoad and viewWillAppear in iOS?

Answer:

• viewDidLoad: Called once when the view is loaded into memory, used for initial setup.

• viewWillAppear: Called every time the view is about to appear on screen, useful for updating UI.

Que 9. How does Core Data work in iOS?

Answer: Core Data is a persistence framework used to manage the model layer of an application. It allows storing, fetching, and manipulating data locally using an object graph and can save data to SQLite, binary, or in-memory stores.

Que 10. What is the difference between UITableView and UICollectionView?

Answer:

• UITableView: Displays data in a single column of rows.

• UICollectionView: Displays data in a flexible grid or custom layouts, offering more customization.

Que 11. What is the difference between @escaping and @autoclosure in Swift?

Answer:

• @escaping: Indicates that a closure can be called after the function it’s passed to returns.

• @autoclosure: Automatically wraps an expression into a closure without explicit syntax.

Que 12. What are Codable and Decodable in Swift?

Answer: Codable is a type alias for Encodable and Decodable protocols. They are used to convert objects to and from JSON or other external representations.

Que 13. What is the difference between struct and class in Swift?

Answer:

• Struct: Value type, copied on assignment, cannot inherit from other structs.

• Class: Reference type, passed by reference, supports inheritance.

Que 14. What is KVO in iOS?

Answer: KVO (Key-Value Observing) is a mechanism for observing changes to properties of an object, enabling data binding between components.

Que 15. How does NotificationCenter work?

Answer: NotificationCenter allows broadcasting and observing events across different parts of an app without direct references. Observers register for specific notifications and execute actions when notifications are posted.

Que 16. What is the difference between synchronous and concurrent queues in GCD?

Answer:

• Synchronous queue: Executes tasks in sequence, waiting for each task to finish.

• Concurrent queue: Executes multiple tasks simultaneously without waiting for one to complete.

Que 17. What is lazy property in Swift?

Answer: A lazy property is only initialized when it is first accessed, useful for delaying expensive operations until they are needed.

Que 18. What is the difference between URLSession and Alamofire?

Answer:

• URLSession: Native iOS API for making network requests.

• Alamofire: Third-party library that simplifies network calls with higher-level abstractions.

Que 19. What is the purpose of SceneDelegate in iOS?

Answer: SceneDelegate manages multiple UI scenes in an iOS app, allowing support for multi-window environments introduced in iOS 13.

Que 20. How does iOS handle background tasks?

Answer: iOS handles background tasks using background fetch, silent push notifications, and BackgroundTasks framework to perform work when the app is not active.

Que 21. What is Combine framework in iOS?

Answer: Combine is a reactive programming framework for handling asynchronous events through publishers and subscribers, enabling better chaining and transformation of data streams.

Que 22. What is SwiftUI and how is it different from UIKit?

Answer: SwiftUI is a declarative framework for building UIs using Swift code. It differs from UIKit, which is imperative and requires manual UI updates.

Que 23. What is an extension in Swift?

Answer: An extension adds new functionality to an existing class, struct, enum, or protocol without subclassing or altering the original source code.

Que 24. What is @State in SwiftUI?

Answer: @State is a property wrapper that allows SwiftUI to track and update a view when the property value changes.

Que 25. How do you secure sensitive data in iOS apps?

Answer: Sensitive data is secured using Keychain services, encryption, and secure APIs like Secure Enclave. Developers should also follow App Transport Security (ATS) guidelines.

You can also Download the PDF from here: iOS Interview Questions PDF

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