iOS Interview Questions to Ask Before You Hire

13 iOS interview questions — with what to listen for

1. 1

   Explain ARC and how retain cycles happen. Where have you actually leaked memory, and how did you find it?

   What a strong answer covers

   Reference counting with strong references keeping objects alive; cycles via closures capturing self and delegate patterns without weak references. Detection through Instruments' leaks and allocations tools or the memory graph debugger. The lived example matters — closure capture in a network callback is the classic confession.

2. 2

   When do you use weak versus unowned, and what happens when each assumption breaks?

   What a strong answer covers

   weak for optional relationships that can outlive each other, becoming nil safely; unowned when the reference is guaranteed to exist, crashing if wrong. A senior answer defaults to weak in closures and treats unowned as a documented performance decision, not a habit.

3. 3

   Walk me through Swift structured concurrency — async/await, tasks, and actors. What real problems did it solve in your code?

   What a strong answer covers

   async/await replacing completion-handler pyramids, Task and task groups for parallelism, actors serializing access to mutable state, MainActor for UI. Real-problem stories usually involve race conditions or callback hell eliminated. Sendable-checking pain and data-race safety migration show current experience.

4. 4

   SwiftUI or UIKit for a new feature in an existing UIKit app — how do you decide, and how do the two interoperate?

   What a strong answer covers

   SwiftUI as the default for new surfaces with UIHostingController embedding, UIViewRepresentable in the other direction, and honest limits: complex collection behaviors, fine-grained control, or minimum-OS constraints keeping UIKit in play. Incremental adoption over rewrites is the judgment being tested.

5. 5

   How does SwiftUI's state system work — State, Binding, ObservableObject or Observable, Environment — and what goes wrong when it is misused?

   What a strong answer covers

   State for local ownership, Binding for shared mutation, observable models for reference-type state, Environment for tree-wide dependencies. Misuse symptoms: view bodies recomputing excessively, state resetting from identity changes, or business logic bleeding into views. The Observable macro reference indicates currency.

6. 6

   A screen in your app janks while scrolling. Describe your investigation on-device.

   What a strong answer covers

   Instruments (Time Profiler, Core Animation), checking main-thread work — image decoding, layout thrash, synchronous fetches — cell reuse in lists, offscreen rendering from shadows and corner radii, and hangs detection. Measuring before fixing and on real hardware, not simulator, is the method being graded.

7. 7

   How do you persist data on iOS, and how do you choose between the options?

   What a strong answer covers

   UserDefaults for small preferences, Keychain for secrets, files for blobs, Core Data or SwiftData for structured object graphs, SQLite/GRDB when SQL control matters. Migration handling and background-context threading rules for Core Data are the depth markers.

8. 8

   Describe your networking layer — how do you structure API calls, auth, retries, and error surfaces?

   What a strong answer covers

   URLSession with async/await, typed endpoint definitions, decodable models with tolerant parsing, token refresh handled once centrally, retry with backoff for idempotent calls, and errors mapped into user-meaningful states. A testable protocol-bound design rather than singletons everywhere is the senior shape.

9. 9

   What is your approach to app architecture — MVVM, TCA, MVC, or something else — and how do you keep view controllers or views from bloating?

   What a strong answer covers

   A coherent, consistently applied pattern with dependency injection and separation of presentation from business logic; pragmatism about matching architecture to team size. Massive-view-controller war stories with the refactor described are more convincing than acronym citations.

10. 10

    How do background execution and app lifecycle really work on iOS, and where have they bitten you?

    What a strong answer covers

    Scene and app lifecycle states, limited background time, BGTaskScheduler for deferred work, background URLSession for transfers, and push-triggered wakes. Bites usually involve tasks killed mid-write or timers that never fire — recovery via checkpointing and idempotent operations is the mature answer.

11. 11

    Take me through your release process: signing, TestFlight, phased release, and what you watch after shipping.

    What a strong answer covers

    Automated builds and signing (fastlane or Xcode Cloud), internal then external TestFlight rings, App Review guideline awareness with a rejection story and resolution, phased rollout, and crash-rate plus key-metric monitoring with a halt-and-hotfix plan. Store operations knowledge is expensive to learn live — this question prices it.

12. 12

    How do you test iOS code — what is unit-testable, what needs UI tests, and how do you make view models testable?

    What a strong answer covers

    XCTest with injected dependencies making view models and services testable without UI, snapshot tests for visual components, and a thin XCUITest layer for critical journeys given its speed and flakiness costs. Testing async code with expectations or async test support is the practical detail.

13. 13

    The app must support the last three iOS versions. How does that constraint shape your technical choices?

    What a strong answer covers

    API availability checks, feature-flagging newer capabilities, dependency minimums, and the real decision cost: SwiftUI and concurrency features gated by OS floor. Candidates who ask about your user base's OS distribution before answering are showing the right instinct.

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