Uncommon and Unique iOS Interview Questions for Intermediate Candidates

When hiring for intermediate iOS positions, it's crucial to evaluate more than just technical proficiency alone. Uncommon and unique interview questions can help gauge deeper insights into a candidate's technical knowledge, problem-solving skills, and ability to work collaboratively. Below, we explore a range of questions that go beyond the usual and provide valuable insights into the candidate's experience and capabilities.

Technical Questions

1. Memory Management

Question: Explain how ARC (Automatic Reference Counting) works in Swift. What are some common pitfalls developers might encounter with ARC?

Answer: ARC in Swift automatically manages the memory by keeping track of the retain count of an object and freeing memory when it is no longer needed. Developers can still encounter issues such as memory leaks due to circular references or over-retaining objects. It's important to avoid strong references within optional properties or closures where possible to prevent these issues.

2. Concurrency

Question: How would you manage a situation where multiple threads need to read and write to a shared resource? Discuss the pros and cons of using GCD vs. NSOperation.

Answer: For managing threads, GCD is generally more efficient and flexible, especially for simple tasks. However, NSOperation is more suitable for complex operations and can manage dependencies between them more easily. GCD, on the other hand, is simpler to use for quick tasks and doesn't require subclassing.

3. Design Patterns

Question: Can you describe a situation where you applied the MVVM (Model-View-ViewModel) pattern in your iOS projects? What were the challenges and how did you overcome them?

Answer: In MVVM, the Model represents the data, the View represents the UI, and the ViewModel acts as a mediator between the two. A common challenge is keeping the UI up-to-date with the model. To address this, I used KVO (Key-Value Observing) or delegates to notify the ViewModel of changes, ensuring that the UI is always in sync with the model. Another challenge is maintaining a clean separation, which I achieved through thorough design and systematic architecture planning.

4. Swift Features

Question: What are property wrappers in Swift? Can you provide an example of how you would use one in a project?

Answer: Property wrappers allow you to encapsulate logic around properties, such as logging or validation. An example might involve creating a `@Logged` wrapper to log the value of a property whenever it is set. This can be particularly useful in debugging by adding transparency to property assignments. For instance, if you have a `@Logged` wrapper around a `userId` property, every time it is updated, the system logs the change, aiding in tracing data flow and verifying values.

5. Performance Optimization

Question: How would you identify and address performance issues in an iOS app? Share specific tools or techniques you would utilize.

Answer: Identifying performance issues involves profiling the app to understand bottlenecks. Instruments in Xcode provides vital tools like Time Profiler, Allocations, and Core Animation Tracer. Techniques can include optimizing algorithms, reducing memory usage, minimizing UI updates, and leveraging caching strategies. Depending on the issue, I may also employ lazy loading or asynchronous loading to improve performance and user experience.

6. Networking

Question: Describe how you would implement a robust API client in Swift. What strategies would you use for error handling and data caching?

Answer: To implement a robust API client, I use frameworks like Alamofire or URLSession. For error handling, I employ a combination of custom error types and try-catch blocks to catch and handle network errors, decoding errors, and any other exceptions. Caching strategies include local storage using Core Data or Realm, or using in-memory caching with a solution like AlamofirePersist. This ensures that frequent API calls are cached locally, reducing the need for subsequent network requests.

Behavioral Questions

Problem-Solving

Question: Tell me about a time you faced a challenging bug in your iOS app. How did you diagnose and resolve it?

Answer: I faced a bug where a complex view controller was causing drastic performance drops. By using debugger tools in Xcode, I isolated a specific line of code causing an unnecessary redraw of the view. Refactoring the view by separating it into smaller, more manageable parts significantly improved performance. This experience taught me the importance of modular code and the value of systematic debugging.

Collaboration

Question: Describe a situation where you had to work with designers or product managers to implement a feature. How did you ensure that the technical implementation met the design specifications?

Answer: When working with a designer to implement a new feature, I ensured alignment by creating wireframes and mockups. This collaboration helped in understanding not only the visual aspects but also the technical requirements. I used version control systems to manage changes, regularly updated the team on progress, and provided clear documentation to ensure all stakeholders were on the same page. This approach ensured that the technical implementation met the design specifications without unnecessary delays.

Learning and Growth

Question: What new iOS technology or framework have you recently learned about? How did you go about learning it, and how do you plan to utilize it in your work?

Answer: One new technology I learned is SwiftUI, which simplifies UI development. I learned it through Apple's official documentation and online tutorials. To apply this, I started by building smaller projects, such as simple UI components, before integrating SwiftUI into existing apps to improve the overall user interface. This not only helped in learning new skills but also enhanced my app's performance and user experience.

System Design Questions

1. App Architecture

Question: Design an architecture for a simple social media app. What components would you include and how would they interact?

Answer: For a social media app, I would include components such as a backend service, a caching layer, a database, and a front-end client. The backend service handles user authentication and API requests, the caching layer stores frequently accessed data to reduce load on the database, and the database stores user data and posts. The front-end client (iOS app) interacts with the backend via APIs, serving the UI to the user. This architecture ensures a scalable and efficient system by offloading common data and reducing server load.

2. Feature Development

Question: If you were tasked with implementing a chat feature in an existing app, what considerations would you take into account regarding scalability and user experience?

Answer: Implementing a chat feature involves several considerations. For scalability, I would ensure the backend supports real-time communication using protocols like WebSockets or MQTT. To improve user experience, I would focus on optimizing message delivery, implementing message threading, and ensuring quick response times. Additionally, I would consider user privacy and security by implementing end-to-end encryption and secure data storage.

3. Scenario-Based Questions

1. Debugging

Question: Imagine your app crashes on launch. What steps would you take to debug this issue?

Answer: To debug a crash on launch, I would first check for errors in the console and use Xcode’s debugger to step through the code. I would then look for any missing symbols or frameworks, inspect the app’s launch settings, and ensure all dependencies are correctly included. Additionally, I would review any recent changes made to the codebase, such as restructured classes or new libraries, to identify potential issues. If the problem persists, I might seek help from team members or online forums, providing them with detailed information, such as system logs and error messages.

2. Code Review

Question: If you were reviewing a colleague’s code, what specific aspects would you focus on to ensure code quality and maintainability?

Answer: During a code review, I would focus on several key aspects: code readability and structure, adherence to coding standards, error handling and logging, and overall maintainability. I would also check for potential bugs, resource leaks, and performance issues. Additionally, I would review the use of design patterns and ensure that the code is modular and extensible, making future updates and maintenance easier.

3. Handling Legacy Code

Question: How would you approach working with legacy code in an iOS project? What strategies would you employ to refactor or improve it?

Answer: When working with legacy code, I would start by documenting the existing codebase to understand its structure and functionality. I would then refactor the code in small incremental steps, focusing on readability and modularity. I would use best practices for modern iOS development, such as iOS 13 and Swift 5, to gradually improve the codebase. Tools like Xcode’s Refactor feature and third-party tools like SourceKit can be particularly helpful during the refactoring process.