Question 1
Difficulty: medium
Can you walk me through how you would design a new feature in an iOS app from requirements to release?
Sample answer
I usually start by clarifying the user problem, success metrics, and any technical constraints. Before writing code, I like to map out the user flow, identify the screens involved, and define what data needs to move through the app. If the feature affects multiple layers, I’ll break it into UI, business logic, networking, and persistence so the implementation stays manageable. I also look for edge cases early, like offline behavior, loading states, and permissions. From there, I build a small technical plan, estimate the work, and confirm it with product and design. During implementation, I prefer to keep the code modular and testable, and I’ll add unit tests around the important logic. Before release, I verify analytics events, performance, and accessibility, then test on multiple device sizes and iOS versions. I’ve found that this process reduces surprises and makes handoff to QA much smoother.
Question 2
Difficulty: medium
How do you decide when to use SwiftUI versus UIKit in an iOS project?
Sample answer
I decide based on the project’s current codebase, team experience, and the complexity of the UI requirements. If I’m building a new screen in an app that is already mostly SwiftUI, I’ll usually stay consistent with that approach. SwiftUI is great for fast iteration, cleaner state-driven UI, and simpler layouts. But if the app depends on advanced collection views, very custom transitions, or a large existing UIKit architecture, UIKit can still be the better choice. I also consider long-term maintenance. If the team is comfortable with SwiftUI and the feature benefits from its declarative style, I’d lean that way. If not, forcing SwiftUI into the wrong context can create unnecessary complexity. In mixed-codebase environments, I’m comfortable bridging the two when needed. My goal is always to choose the tool that gives the best balance of performance, maintainability, and development speed for that specific feature.
Question 3
Difficulty: hard
Describe a time you had to debug a difficult crash in an iOS app. How did you approach it?
Sample answer
When I run into a crash, I try to avoid guessing and work from evidence. In one project, we had an intermittent crash that only appeared in production on a small percentage of devices. I started by reviewing the crash logs and symbolicated stack traces to identify the most likely area of failure. Then I looked at recent changes, especially anything involving threading or optional handling, since those are common sources of hard-to-reproduce issues. I added extra logging around the suspected path in a staging build and tried to reproduce the issue using similar device conditions and data. It turned out to be a race condition caused by updating UI state from a background thread after an async network response. Once I confirmed that, I fixed the threading issue, added a regression test, and reviewed other similar code paths. I’ve learned that the most effective debugging combines logs, code review, and disciplined narrowing of the problem.
Question 4
Difficulty: medium
How do you ensure your iOS code is maintainable when working on a large app with multiple developers?
Sample answer
For larger apps, I focus on structure and consistency because they have a bigger impact than clever code. I prefer separating responsibilities clearly, so views don’t accumulate business logic and networking stays outside the UI layer. I’m a fan of using patterns that fit the team, such as MVVM or a clean architecture approach, as long as they make the code easier to understand rather than more abstract. I also try to keep modules small and reusable, with naming and file organization that make ownership obvious. Code reviews are important too; I look for readability, duplication, and whether a change introduces hidden coupling. On the team side, I like agreeing on standards for error handling, dependency injection, testing, and async patterns so everyone builds in a consistent way. That usually pays off later when multiple people need to work in the same area without stepping on each other’s changes.
Question 5
Difficulty: medium
What steps do you take to optimize performance in an iOS app?
Sample answer
I start by identifying where the slowdown actually is, because performance issues can come from rendering, networking, memory use, or expensive work on the main thread. I’ll use Instruments, Time Profiler, and the main thread checker to find bottlenecks rather than assuming the problem. If scrolling feels slow, I look at image loading, cell reuse, view hierarchy depth, and any repeated calculations. For networking-heavy features, I check caching, request batching, and whether we can defer unnecessary refreshes. Memory issues are another area I watch closely, especially retain cycles, large images, and objects that stick around longer than expected. I also try to be careful with animations and layout updates, since those can hurt responsiveness if overused. In practice, I’ve found small improvements add up quickly. My rule is to measure before and after each change so I know whether the optimization actually helped the user experience.
Question 6
Difficulty: medium
How would you handle a situation where product wants a feature delivered quickly, but you believe the implementation needs additional technical work?
Sample answer
I’d be transparent and focused on tradeoffs. If the requested timeline is aggressive, I’d explain what makes the feature risky and what could happen if we rush it, such as bugs, poor performance, or difficult maintenance later. At the same time, I’d try to offer options instead of just saying no. For example, I might suggest a smaller first release, a temporary technical solution, or splitting the work into a user-facing version now and a more robust version later. I find it helps to frame the conversation around impact: what gives the user value fastest while protecting quality. If the risk is acceptable, I’m comfortable shipping a simpler implementation with clear follow-up work. If it could cause serious issues, I’d push harder for the extra time. In my experience, product teams respond well when you bring alternatives and explain the engineering cost in practical terms rather than just technical jargon.
Question 7
Difficulty: hard
Tell me about your experience with asynchronous programming in Swift. How do you use it safely?
Sample answer
I use async programming a lot, especially for networking and any work that shouldn’t block the main thread. In Swift, I’m comfortable with async/await, Task, TaskGroup, and also Combine when it fits the architecture. My main priority is keeping UI updates on the main thread and making sure the logic stays easy to follow. With async/await, I like how readable the code becomes compared to deeply nested callbacks, but I still pay attention to cancellation, error propagation, and task lifecycles. If a user navigates away from a screen, I want to make sure background work can stop cleanly. I also avoid shared mutable state whenever possible, since concurrency bugs can be subtle. When needed, I’ll use actors or other synchronization techniques to protect state. Safe async code, in my view, is not just about using the newest API; it’s about designing flows that are predictable, cancelable, and easy to reason about during maintenance.
Question 8
Difficulty: medium
How do you test iOS features, and what do you usually automate?
Sample answer
I try to cover the most important behavior at the right level. For business logic, I like unit tests because they’re fast and good at catching regressions early. That includes things like validation, formatting, state transitions, and view model behavior. For integration points such as networking or persistence, I’ll add tests where they provide real value, often by mocking dependencies or using test doubles. I also think UI tests are useful, but I’m selective with them because they can be slower and more brittle. I usually automate the critical user paths, such as sign-in, checkout, or any flow that would be expensive to break in production. Beyond automated tests, I still do manual checks for accessibility, device compatibility, and edge cases like poor connectivity. I’ve found that a balanced testing strategy works better than trying to automate everything. The goal is confidence, not just a big test count.
Question 9
Difficulty: medium
How do you approach accessibility in iOS development?
Sample answer
I treat accessibility as part of building a good product, not as an extra step at the end. At the UI level, I make sure interactive elements have proper labels, hints, and traits so VoiceOver users can understand them easily. I also check that text scales correctly with Dynamic Type and that layouts remain usable at larger font sizes. Color contrast matters too, especially for users with low vision or when the device is in different appearance modes. If a screen relies heavily on color or animation, I look for other ways to communicate status or hierarchy. I try to test with VoiceOver and other accessibility settings while developing, because issues are much easier to fix early. In code review, I also watch for custom controls that might need extra accessibility configuration. For me, accessibility is not only about compliance. It improves the product for everyone, especially users in situations where clarity and simplicity matter.
Question 10
Difficulty: medium
What would you do if you joined a new iOS team and found a codebase with little documentation and inconsistent patterns?
Sample answer
I’d start by learning how the app actually works before trying to change it. My first goal would be to identify the key modules, the app’s architecture, and the most important user flows. I’d read through the code, run the app, and trace a few features end to end to understand the dependencies. If the patterns are inconsistent, I wouldn’t try to rewrite everything right away. Instead, I’d look for one area where I could make a meaningful improvement, such as adding tests, cleaning up a confusing module, or documenting a repeated pattern the team can reuse. I’d also ask teammates where the pain points are, because they usually know which parts of the codebase cause the most friction. Over time, I’d aim to introduce consistency through incremental changes and code review rather than big disruptive refactors. That approach helps me add value quickly without creating risk for the team.
