Interview Questions for a Mobile App Developer

Walk me through how you would design an offline-first data layer for an app that must work without connectivity and reconcile changes when the user comes back online.

What to look for: A clear approach to local storage (SQLite, AsyncStorage, Hive), a sync queue, conflict resolution strategy (last-write-wins vs merge), and handling partial failures and retries.

An app screen drops below 60fps while scrolling a long list. How do you diagnose and fix it?

What to look for: Use of render profiling tools, list virtualization (FlatList/RecyclerView), avoiding unnecessary re-renders, image decode/caching, and measuring before and after rather than guessing.

How do you decide between cross-platform (React Native or Flutter) and native development for a new project?

What to look for: Trade-offs around team skills, performance-critical features, platform-specific APIs, time-to-market, and maintenance cost — not a dogmatic answer either way.

Describe how you integrate push notifications across FCM and APNs, including handling token lifecycle and a notification arriving while the app is backgrounded or killed.

What to look for: Token registration and refresh, server-side targeting, foreground vs background handling, deep-linking from a tap, and dealing with permission denial.

How do you shape requests with backend engineers so payloads stay mobile-friendly, and how do you cache GraphQL or REST responses?

What to look for: Pagination, trimming over-fetching, payload size awareness, cache invalidation strategy, and collaboration on API shapes rather than accepting whatever the backend returns.

What is your approach to reducing cold app startup time?

What to look for: Deferring non-critical init, lazy-loading modules, measuring with traces, reducing main-thread work, and optimizing the first-frame render path on lower-end devices.

Tell me about an app you shipped end to end. What was your role in the release cycle, from code signing to store submission?

What to look for: Ownership of build configurations, signing for both iOS and Android, navigating review, and handling a rejection or expedited release.

Describe a serious production crash or ANR you investigated. How did you find the root cause and what did you change?

What to look for: Use of Sentry/Firebase Crashlytics, reproducing the issue, reading stack traces, and a concrete fix plus prevention (tests, monitoring) afterward.

Tell me about a time you had to support a wide range of devices or OS versions. How did you handle the fragmentation?

What to look for: Concrete device-tier testing, graceful degradation, feature flags, and prioritizing fixes by real user impact from analytics.

Give an example of a performance or memory problem you solved that meaningfully improved the user experience.

What to look for: A measured baseline, a specific intervention (image handling, leaks, background work), and a quantified improvement the team could see.

Crash-free sessions suddenly drop after a release. How do you respond in the first hour?

What to look for: Checking crash dashboards by version and device, deciding whether to halt rollout or hotfix, communicating to stakeholders, and a staged rollback plan.

A third-party SDK for payments adds significant app size and a startup delay. How do you decide whether to keep it?

What to look for: Weighing bundle/startup impact against feature value, lazy initialization, evaluating alternatives, and measuring rather than assuming.

Users on older Android devices report the app feels sluggish, but it's fine on your test phone. How do you proceed?

What to look for: Acquiring or emulating lower-end hardware, profiling on it, examining memory and frame timing, and targeting fixes to the affected segment.

Apple rejects your build during review for a policy reason close to launch. What do you do?

What to look for: Reading the rejection carefully, addressing the specific guideline, communicating the timeline, and using expedited review or a compliant workaround.

How do you work with designers to keep an implementation faithful to the design while respecting platform conventions like HIG and Material Design?

What to look for: Balancing pixel fidelity with native patterns, flagging conflicts early, and using a shared component library or design tokens.

How do you decide what to cover with unit and widget tests versus manual testing on a mobile project?

What to look for: Testing critical logic and UI components, recognizing the cost of brittle UI tests, and a pragmatic risk-based split.

Tell me how you keep backend engineers aligned on mobile constraints during planning.

What to look for: Proactively raising payload size, offline needs, and battery/data impact early, and negotiating API shapes rather than absorbing problems later.

How do you keep mobile analytics and crash reporting useful for the whole team rather than noise only you read?

What to look for: Meaningful event taxonomy, alerting on crash-free rate and ANRs, sharing release health, and turning Firebase, Sentry, or Amplitude data into decisions others can act on.