Interview guide
Mobile Developer Interview Questions & Answers Guide (2026)
A hiring-manager’s interview kit for mobile developers — with specific “what to look for” notes on every answer, red flags to watch, and a practical test.
Key facts
- Role
- Mobile Developer
- Technical questions
- 14
- Behavioral
- 7
- Role-fit
- 5
- Red flags
- 8
- Practical test
- Included
How to use this guide
Pick 4-6 technical questions across difficulties, 2-3 behavioral, and 1-2 role-fit for a 45-minute interview. For senior roles, weight harder technical and role-fit higher. Always close with the practical test so you are hiring on evidence, not impressions. The “what to look for” notes are a scoring rubric: strong answers touch most points, weak answers miss them or replace them with platitudes.
Technical questions — Medium
1. Walk me through the iOS app lifecycle from cold launch to backgrounded. Where would you register for push notifications, and why not in application(_:didFinishLaunchingWithOptions:)?
MediumWhat to look for: Clear explanation of willFinishLaunching, didFinishLaunching, sceneDidBecomeActive, sceneWillResignActive, background transitions. Should argue push registration should follow a contextual onboarding prompt, not blast on launch, to protect grant rates.
2. On Android, what is the difference between a cold start, a warm start, and a hot start, and what is your budget for each on a Pixel 6a?
MediumWhat to look for: Cold = process and Application created; warm = process alive, Activity recreated; hot = Activity resumed. Budgets around 2s/1s/<500ms. Should mention baseline profiles, Startup Initializer, and Android Vitals.
3. App Store rejected your build for Guideline 4.3 (spam) — what do you do?
MediumWhat to look for: Real playbook: read the exact rejection message, respond in Resolution Center with differentiation evidence, often request a call with App Review, fix superficial similarity issues, resubmit. Should have actual war story.
4. How do you implement deep linking so that tapping a push notification opens a specific screen deep in the nav stack, even on cold start?
MediumWhat to look for: URL scheme vs universal links/App Links, parsing payload in didReceive, pending deep-link queue if auth not ready on cold start, deferred navigation until root is mounted. Android: intent filters and onNewIntent.
5. How do you securely store a refresh token on iOS and Android?
MediumWhat to look for: Keychain on iOS (kSecAttrAccessibleAfterFirstUnlockThisDeviceOnly), Android Keystore + EncryptedSharedPreferences. Should NOT say UserDefaults or SharedPreferences plain. Mention biometric-gated retrieval for sensitive actions.
6. Your crash-free session rate dropped from 99.7% to 98.2% after a release. Walk me through triage.
MediumWhat to look for: Crashlytics/Sentry release comparison, top crashes by affected users, symbolication check (dSYM/ProGuard mapping uploaded?), phased release halt, hotfix vs rollback decision, expedited review request.
7. What is the difference between a foreground service, a background service, and WorkManager on Android? When do you use each?
MediumWhat to look for: Foreground for user-visible ongoing work (notification required), background services deprecated post-O, WorkManager for deferrable guaranteed execution with constraints (network, charging). Should cite Doze and App Standby impact.
8. How would you reduce your app binary size if it crossed the 200 MB cellular download cap?
MediumWhat to look for: App thinning, on-demand resources, asset catalog optimization, dead code stripping, strip debug symbols, evaluate bitcode/unused architectures, WebP over PNG, Android App Bundle with dynamic delivery.
Technical questions — Hard
1. Your app leaks memory — Instruments shows retained closures. Walk me through diagnosis and fix in Swift.
HardWhat to look for: Instruments Leaks + Allocations, identify strong reference cycles, [weak self] or [unowned self] in closures, breaking cycles in Combine subscriptions, proper cancellable storage. Should mention Memory Graph Debugger.
2. Design an offline-first note-taking feature. User writes on subway, syncs when WiFi returns, another device edited the same note. Walk me through data model, conflict resolution, and sync.
HardWhat to look for: Local persistence (Core Data/Room/SQLite), lastModified timestamps or vector clocks, server-side conflict resolution (LWW, CRDTs, manual merge UI), optimistic UI, retry queue, idempotent mutation endpoints.
3. Walk me through a StoreKit 2 subscription purchase flow end to end, including server-side receipt validation and restoring purchases.
HardWhat to look for: Product.products(for:), purchase(), verification result with JWS, App Store server notifications v2 webhook, RevenueCat or custom receipt store, Transaction.currentEntitlements on launch, restorePurchases for family sharing/new device.
4. Implement biometric authentication with Face ID. What happens if the user disables Face ID in Settings after enrolling with your app?
HardWhat to look for: LAContext canEvaluatePolicy, handling LAError codes (biometryNotAvailable, biometryLockout, userFallback), keychain access control flags, fallback to passcode, invalidation of biometric-gated keys when enrollment changes.
5. In React Native, how do you keep JS thread performance from blocking animations at 60fps?
HardWhat to look for: Reanimated 3 worklets on UI thread, useNativeDriver for Animated, avoiding heavy work on bridge, FlatList with getItemLayout + removeClippedSubviews, Hermes, profiling with Flipper/React DevTools.
6. Tell me about the worst App Store rejection you fought through. What was the fix?
HardWhat to look for: Specific: guideline cited, what the reviewer wrote, what they changed, how long it took. Good answers show diplomatic Resolution Center communication and willingness to escalate via App Review Board when correct.
Behavioral questions
1. Describe a release where you caught a critical bug in TestFlight/beta and held the release. How did you make that call?
What to look for: Clear severity judgment, communicated trade-off to stakeholders, data-driven (crash rate, affected users), did not cave to schedule pressure on a real P0.
2. Tell me about a time you disagreed with product about a platform convention (e.g., they wanted iOS to behave like Android).
What to look for: Advocated for HIG/Material guidelines with user impact reasoning, proposed compromise, respected the final call. Shows platform craft.
3. Walk me through a memory or performance bug that took you more than a day to find.
What to look for: Specific tooling (Instruments, Profiler), hypotheses formed and eliminated, root cause explained causally. Not a vibes-based fix.
4. How do you handle flaky device-specific bugs that only reproduce on one OEM?
What to look for: Firebase Test Lab, BrowserStack App Live, remote debug sessions, willingness to buy/borrow the device. Does not dismiss OEM quirks as not-my-problem.
5. Describe a time you had to learn a second mobile platform quickly. How did you ramp up?
What to look for: Structured learning, pairing with a senior on that platform, shipping small PRs first, humility about ramp time estimate.
6. How do you keep your code review comments useful without being pedantic?
What to look for: Separates blockers from nits, explains the why, asks rather than decrees, praises good choices.
7. Tell me about a production incident you owned end to end — detection, fix, postmortem.
What to look for: Ownership, detection timeline, rollback decision, blameless postmortem, guardrails added after. No blame-shifting.
Role-fit questions
1. Native vs React Native vs Flutter — what do you actually reach for on a new project and why?
What to look for: Pragmatic answer based on team size, feature requirements, hardware access needs. No religious wars. Has an opinion but not a dogma.
2. We ship iOS-first and Android 2 weeks behind. How does that change how you write code?
What to look for: Shared backend contracts, feature flags for platform parity tracking, avoiding iOS-only terminology in shared specs, willing to QA both.
3. How do you feel about carrying a release pager for store rejections that come in overnight your time?
What to look for: Realistic: willing to own but defines scope. Proposes runbooks so others can cover rotation. Not a martyr.
4. What does your first 30 days look like to feel productive on our codebase?
What to look for: Clone, build locally on both platforms, provisioning walkthrough, ship a small PR in week 1, own a feature by week 3. Red flag: expects weeks of onboarding with no output.
5. Our QA team is offshore too — how do you partner with them on a release?
What to look for: Early TestFlight builds, written test plan review, triage calls during overlap, writes repro-friendly logs, treats QA as peer.
Red flags
Any one of these alone is usually reason to pass, especially combined with weak answers elsewhere.
- • Has never shipped an app to the App Store or Google Play under their own name or a client name they can reference.
- • Cannot describe a single App Store rejection and how they recovered.
- • Stores auth tokens in UserDefaults or SharedPreferences plain text.
- • Does not know what dSYM or ProGuard mapping upload does and why symbolication matters.
- • Claims "I always use force unwrap, it is fine" in Swift or ignores nullability in Kotlin.
- • Has never used Instruments, Android Profiler, or equivalent — debugs performance by vibes.
- • Copies SDK integration code from docs without reading background mode, permissions, or lifecycle implications.
- • Dismisses accessibility (VoiceOver, TalkBack, Dynamic Type) as a nice-to-have.
Practical test
6-hour take-home: build a small image-browser app (iOS or Android native, or React Native/Flutter) that fetches a paginated image feed, caches locally for offline browsing, supports pull-to-refresh, and shows image detail on tap with a deep-link URL that survives cold start. Requirements: handles network failures gracefully, includes at least 3 unit tests, passes VoiceOver/TalkBack on list and detail screens, and ships a signed TestFlight or Play Internal build. Graded on: architecture (30%), offline/caching correctness (25%), accessibility (15%), tests (15%), and the README explaining trade-offs (15%).
Scoring rubric
Score each answer 1-4: (1) Misses most of the rubric or gives platitudes; (2) Hits some points but cannot go deep when pressed; (3) Covers the rubric and can defend the answer under follow-ups; (4) Adds unprompted nuance, trade-offs, or real examples beyond the rubric. Hire at an average of 3.0+ across technical, behavioral, and role-fit, with zero red flags, and a pass on the practical test.
Related
Written by Syed Ali
Founder, Remoteria
Syed Ali founded Remoteria after a decade building distributed teams across 4 continents. He has helped 500+ companies source, vet, onboard, and scale pre-vetted offshore talent in engineering, design, marketing, and operations.
- • 10+ years building distributed remote teams
- • 500+ successful offshore placements across US, UK, EU, and APAC
- • Specialist in offshore vetting and cross-timezone team integration
Last updated: April 12, 2026