Top 10 Senior iOS Engineer Interview Questions & Answers in 2024

1. How do you implement efficient data persistence in an iOS app, and what are the advantages and disadvantages of using Core Data versus Realm?

Core Data is an object graph and persistence framework that provides a powerful and flexible way to manage data in your app. It supports various data models, relationships, and query capabilities. On the other hand, Realm is a mobile database that is faster than Core Data, particularly for read and write operations. Core Data is integrated with the Apple ecosystem, but Realm offers better performance and a simpler API.

2. Explain the concept of Key-Value Observing (KVO) in iOS and provide a scenario where you might use it.

Key-Value Observing is a mechanism in Cocoa and Cocoa Touch that allows objects to be notified of changes to specific properties of another object. To use KVO, a class must adopt NSObject and use the observeValue(forKeyPath:of:change:context:) method. A scenario for using KVO could be monitoring changes in a model object's properties and updating the UI accordingly.

3. What are App Extensions, and can you provide examples of different types of iOS App Extensions?

App Extensions allow an app to extend functionality beyond its main purpose. Examples of iOS App Extensions include:

• Today Extension (Widget): Provides information in the Today view of the Notification Center.
• Share Extension: Enables content sharing with other apps.
• Action Extension: Allows performing tasks on selected content within other apps.

4. Describe the purpose of Auto Layout in iOS development and how it helps in creating responsive user interfaces.

Auto Layout is a constraint-based layout system that allows you to create dynamic and adaptive user interfaces. It helps in creating responsive UIs by defining relationships between UI elements, ensuring they adapt to various screen sizes and orientations. Auto Layout manages the arrangement and sizing of UI elements, providing a flexible and scalable design.

5. Explain the differences between synchronous and asynchronous tasks in iOS, and when would you choose one over the other?

Synchronous tasks block the execution of code until the task is complete, while asynchronous tasks allow code execution to continue without waiting for the task to finish. Use synchronous tasks for simple and quick operations where blocking the thread is acceptable. Asynchronous tasks are suitable for time-consuming operations, such as network requests, to prevent blocking the main thread and maintain a responsive user interface.

6. What is the Codable protocol in Swift, and how can it be used to serialize and deserialize data?

The Codable protocol is used for encoding and decoding data in Swift. It combines the functionality of the Encodable and Decodable protocols. You can use Codable to serialize Swift objects into JSON or other formats and deserialize data from external representations back into Swift objects. It simplifies the process of converting between Swift objects and external data representations.

7. Discuss the benefits and limitations of using SwiftUI for building user interfaces compared to UIKit.

SwiftUI is a modern declarative framework for building user interfaces, while UIKit is the traditional imperative framework. Benefits of SwiftUI include a concise and readable syntax, real-time previews, and cross-platform compatibility with macOS. However, limitations include a lack of complete feature parity with UIKit, and as of now, it may not be suitable for all complex UI scenarios.

8. Explain the purpose of the AppDelegate and SceneDelegate in an iOS app, and when are they invoked in the app lifecycle?

The AppDelegate manages the app's overall life cycle and is responsible for handling system events, such as launching and terminating the app. The SceneDelegate is responsible for managing the app's UI and is introduced with multi-window support on iPad. They are invoked at various stages of the app lifecycle, with AppDelegate handling overall app events, and SceneDelegate managing UI-related events, especially in a multi-scene environment.

9. Discuss the advantages of using Core ML in iOS applications and provide an example of how it can be integrated for machine learning tasks.

Core ML allows integration of machine learning models into iOS apps, providing on-device processing for tasks like image recognition and natural language processing. Advantages include improved privacy and reduced reliance on network connectivity. To integrate Core ML, you can convert machine learning models into the Core ML format using tools like Core ML Tools and then use the Core ML framework to incorporate them into your app.

10. What are the best practices for handling memory management in Swift, and how does Automatic Reference Counting (ARC) contribute to it?

Swift uses Automatic Reference Counting (ARC) to manage memory. Best practices for memory management include:

• Use optionals wisely to avoid strong reference cycles.
• Utilize weak and unowned references carefully to prevent retain cycles.
• Leverage value types (structs and enums) when appropriate to minimize reference counting.
• Use instruments like the Xcode Memory Graph Debugger to identify and fix memory issues.
• Be mindful of strong reference cycles, especially when working with closures and delegate patterns.