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Mobile App Development Technical Round Questions & Answers

40 questions for the technical round stage — 8 easy, 28 medium, 4 hard.

About the technical round round

The technical round is the core of a Mobile App Development interview: concept questions with follow-ups, a live hands-on task and a deep dive into one of your projects. Interviewers check depth, not just definitions.

Tips for the technical round round

  • Say your approach out loud before you start writing.
  • After a correct answer, expect 'why?' and 'what if?' follow-ups; go one level deeper than the question.
  • Pick one project you can explain end to end, including what you would do differently.
  • If you get stuck, explain what you would try next instead of going silent.
Solved — technical roundStart practicing
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01

What local storage options exist for Flutter and React Native apps?

Mobile Backend, APIs and FirebaseEasy
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For simple key-value settings, Flutter uses shared_preferences and React Native uses AsyncStorage or MMKV. For sensitive data, flutter_secure_storage or expo-secure-store use Keychain and Keystore. For structured data and queries, use SQLite via sqflite or drift in Flutter and expo-sqlite or WatermelonDB in React Native. Object stores like Isar, Hive or Realm also exist, but check maintenance status before choosing.
02

Write a Redux Toolkit slice for a cart.

React Native Navigation, State and Native ModulesMedium
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const cartSlice = createSlice({ name: 'cart', initialState: { items: [] }, reducers: { addItem(state, action) { const existing = state.items.find((i) => i.id === action.payload.id); if (existing) existing.qty += 1; else state.items.push({ ...action.payload, qty: 1 }); }, removeItem(state, action) { state.items = state.items.filter((i) => i.id !== action.payload); }, }, }); export const { addItem, removeItem } = cartSlice.actions; export const selectTotal = (s) => s.cart.items.reduce((t, i) => t + i.price * i.qty, 0);
03

How do push notifications work end to end?

Mobile Backend, APIs and FirebaseMedium
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The app registers with the platform push service, FCM on Android and APNs on iOS, often both through FCM, and receives a device token. The app sends this token to your backend, linked to the user. When an event happens, the backend sends a message to FCM or APNs with the token, which delivers it to the device. The app requests notification permission, handles taps to open the right screen, and refreshes tokens when they change.
04

What are optimistic updates and how do you implement them?

React Native Navigation, State and Native ModulesMedium
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An optimistic update changes the UI immediately as if the server request succeeded, such as liking a post, then rolls back if the request fails. It makes apps feel fast on slow networks. With TanStack Query, use onMutate to update the cache and save the previous value, onError to restore it, and onSettled to refetch. Use it for low-risk actions, not payments.
05

Write a React Navigation setup with a stack containing a tab navigator and a details screen.

React Native Navigation, State and Native ModulesMedium
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const Tab = createBottomTabNavigator(); const Stack = createNativeStackNavigator(); function HomeTabs() { return ( <Tab.Navigator> <Tab.Screen name="Feed" component={FeedScreen} /> <Tab.Screen name="Profile" component={ProfileScreen} /> </Tab.Navigator> ); } export default function App() { return ( <NavigationContainer> <Stack.Navigator> <Stack.Screen name="Home" component={HomeTabs} options={{ headerShown: false }} /> <Stack.Screen name="Details" component={DetailsScreen} /> </Stack.Navigator> </NavigationContainer> ); }
06

How do you detect and fix memory leaks in cross-platform apps?

Testing, Performance and CI/CDMedium
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Leaks usually come from subscriptions, timers, controllers and listeners that are never disposed, or global caches that grow without limits. In Flutter, dispose controllers and cancel stream subscriptions in dispose, and check the DevTools memory view for growing instances. In React Native, return cleanup functions from useEffect and remove event listeners. Repeatedly open and close a screen while profiling to confirm memory returns to baseline.
07

An animation stutters whenever the screen fetches data. How do you fix it?

React Native Navigation, State and Native ModulesHard
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The animation likely runs on the JS thread, and data parsing or re-renders block it. Move the animation to the UI thread with Reanimated or Animated with useNativeDriver, reduce the work done when data arrives by memoising components and normalising state updates, and delay heavy processing with InteractionManager or requestIdleCallback-style scheduling until the animation finishes. Profile with React Native DevTools to confirm.
08

Why do Flutter apps need a state management solution beyond setState?

Flutter State Management and ArchitectureEasy
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setState works for local UI state inside one widget, but shared state like the logged-in user, cart or settings must be read and changed by many screens. Passing it through constructors becomes messy, and rebuilding large trees hurts performance. State management libraries separate business logic from UI, make state testable, rebuild only widgets that depend on changed data, and give a clear, predictable flow of updates.
09

What are over-the-air updates and what are their limits?

App Store and Play Store PublishingMedium
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Over-the-air updates push new JavaScript bundles and assets to React Native apps without a store release, using services like EAS Update. They fix bugs quickly but can only change JavaScript and assets, not native code, permissions or SDK versions, which need a new build. Store policies allow them only if the app's core purpose does not change. Use runtime versions to ensure updates match compatible native builds, and roll out gradually.
10

You are designing a large Flutter app for a bank with 30 developers. How do you structure it?

Flutter State Management and ArchitectureHard
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Split the app into feature packages in a monorepo managed with Melos or pub workspaces, plus core packages for networking, design system, analytics and security. Pick one state management approach, such as Bloc for strict traceability, with clear layer boundaries. Use code generation consistently, enforce lints and architecture tests in CI, and assign feature ownership. Add integration tests for critical journeys and strict security reviews for storage and network code.
11

How do you implement a form with validation in Flutter?

Dart and Flutter BasicsMedium
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Wrap fields in a Form with a GlobalKey<FormState>, use TextFormField with a validator function that returns an error string or null, and call formKey.currentState!.validate() on submit. Use TextEditingController for values and dispose it, set keyboardType and textInputAction for each field, and autovalidateMode onUserInteraction to show errors as the user types. Keep validation rules in testable functions outside widgets.
12

How would you structure the folder layout of a medium-sized cross-platform app?

Mobile Development FundamentalsMedium
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Organise by feature rather than by type: features/auth, features/cart, features/profile, each containing UI, state logic and data code. Keep shared pieces in core folders such as core/network, core/storage, core/theme and core/widgets or components. Put configuration for environments separately. This keeps related code together, makes ownership clear and lets features be moved into packages later. Enforce the structure with lint rules and code review.
13

What is the difference between a BaaS and a custom backend for a mobile startup?

Mobile Backend, APIs and FirebaseEasy
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A Backend-as-a-Service gives ready authentication, database, storage and functions, so a small team launches faster without managing servers, and costs stay low at small scale. A custom backend gives full control over business logic, data model, integrations and cost at large scale, but needs more engineering effort. Many startups begin with BaaS for the MVP and gradually move complex or expensive parts to custom services.
14

What are useMemo, useCallback and React.memo used for?

React Native CoreMedium
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React.memo skips re-rendering a component when its props are shallowly equal. useCallback keeps the same function reference between renders, and useMemo caches a computed value, both only changing when dependencies change. They help when passing callbacks to memoised list items or computing expensive values. Overusing them adds complexity with little gain; the React Compiler can now apply such memoisation automatically in supported projects.
15

How do you handle app-wide theming and dark mode in Flutter?

Flutter State Management and ArchitectureEasy
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Define ThemeData for light and dark modes in MaterialApp, using ColorScheme.fromSeed to generate consistent Material 3 colours, and set themeMode from a settings state, saved in shared preferences. Widgets read Theme.of(context).colorScheme and textTheme instead of hardcoded colours. Add ThemeExtension classes for brand-specific tokens. This keeps the design consistent and makes switching themes a single state change.
16

Compare Provider, Riverpod and Bloc.

Flutter State Management and ArchitectureMedium
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Provider is simple and built on InheritedWidget but depends on BuildContext and can throw provider-not-found errors at runtime. Riverpod, from the same author, is compile-safe, independent of the widget tree, supports async providers and easy overrides for testing. Bloc uses events and states with streams, enforcing strict separation and traceability, popular in large teams and enterprises. Choose based on team familiarity and app complexity.
17

How would you set quality gates before a mobile release?

Testing, Performance and CI/CDHard
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Define clear criteria: all automated tests pass, no open critical or high bugs, crash-free rate in beta above an agreed threshold like 99.5 percent, performance budgets for startup time and app size met, accessibility checks on new screens, and security review for sensitive changes. Run smoke tests on the release build on real devices. Release with a staged rollout and monitor metrics before expanding.
18

How do you handle gestures such as swipe to delete in React Native?

React Native Navigation, State and Native ModulesMedium
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Use react-native-gesture-handler, which processes gestures on the native side, often with Reanimated for smooth animations. For swipe to delete, the Swipeable or ReanimatedSwipeable component renders action buttons behind a row. Define gestures with the Gesture API, such as Gesture.Pan, and compose them when needed. Wrap the app root in GestureHandlerRootView. Provide an accessible alternative like a long-press menu for screen reader users.
19

What are the steps to publish an app on the Play Store?

App Store and Play Store PublishingEasy
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Create a Play Console developer account, create the app and fill in store listing details, screenshots, privacy policy, content rating, data safety and target audience forms. Build a signed release App Bundle with a unique application ID and increasing versionCode, and use Play App Signing. Upload to internal or closed testing first, then promote to production with a staged rollout. New personal accounts must complete a closed test with testers before production access.
20

A React Native list of 2000 items scrolls slowly and shows blank areas. How do you fix it?

React Native CoreMedium
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Use FlatList or FlashList rather than ScrollView with map. Provide a stable keyExtractor, memoise row components with React.memo, avoid inline functions and heavy computation in renderItem, and use getItemLayout or fixed item sizes where possible. Tune windowSize and maxToRenderPerBatch, compress and cache images with a library like expo-image, and test a release build, since dev mode is much slower.
21

How do you measure performance in a Flutter app?

Testing, Performance and CI/CDMedium
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Run the app in profile mode on a real device, not debug or emulator. Use Flutter DevTools: the performance view shows frame build and raster times, the CPU profiler finds expensive functions, and the memory view tracks allocations and leaks. Target under about 16 milliseconds per frame for 60 fps. The performance overlay shows UI and raster thread graphs, and rebuild tracking highlights widgets rebuilding too often.
22

What is app signing and why must you protect the keys?

App Store and Play Store PublishingMedium
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Signing proves the app comes from you and that updates are from the same developer. On Android, you sign uploads with an upload key and Play App Signing re-signs with the app signing key held by the store; a lost upload key can be reset, but losing a self-managed app key meant you could never update the app. On iOS, signing uses certificates and provisioning profiles. Store keys in a secure vault and CI secrets, never in the repository.
23

How do you build a release version of a Flutter app for both stores?

App Store and Play Store PublishingMedium
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flutter build appbundle --release --obfuscate --split-debug-info=build/symbols # Output: build/app/outputs/bundle/release/app-release.aab flutter build ipa --release --obfuscate --split-debug-info=build/symbols # Output: build/ios/ipa/*.ipa, upload with Transporter or xcrun altool # Version comes from pubspec.yaml, for example: # version: 2.3.1+45 (name 2.3.1, build number 45)
24

Explain the core React Native components.

React Native CoreEasy
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View is the basic container, like a div, supporting flexbox layout and styles. Text displays text, and all strings must be inside Text. Image shows images from network or local sources. TextInput handles keyboard input. Pressable handles touches with press states. ScrollView scrolls a small amount of content, while FlatList and SectionList render long lists virtually. SafeAreaView or the safe area context library keeps content away from notches.
25

How do you integrate a payment gateway in a mobile app safely?

Mobile Backend, APIs and FirebaseHard
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Create the order on your backend with the amount, get an order ID, and open the gateway's SDK checkout in the app with that ID. After payment, the SDK returns a payment ID and signature, which the app sends to the backend to verify with the secret key before marking the order paid. Rely on server-side webhooks as the final truth. Never keep secret keys in the app or trust client-side success alone.
26

The cart total shows stale values on the checkout screen after items are removed on the cart screen. How do you fix it?

Flutter State Management and ArchitectureMedium
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Each screen probably holds its own copy of cart data. Move cart state into a single shared state object, such as a Riverpod notifier or a Cubit provided above both screens, and have both screens watch it. All mutations go through that object, which emits a new immutable state. Derived values like total should be computed from the state, not stored separately, so they can never become inconsistent.
27

A global Redux store causes the whole app to re-render on every small change. How do you fix it?

React Native Navigation, State and Native ModulesMedium
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Components are probably selecting large parts of state or creating new objects in selectors. Select only the fields each component needs with useSelector, memoise derived data with createSelector, and keep state normalised. Move server data to RTK Query or TanStack Query and local UI state back into components. Verify improvements with the React profiler, checking which components render after each action.
28

How would you test a Bloc or Riverpod notifier?

Flutter State Management and ArchitectureMedium
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Test business logic without widgets. For Bloc, the bloc_test package's blocTest builds the bloc with a fake repository, acts by adding events, and expects a list of emitted states. For Riverpod, create a ProviderContainer with overrides for repository providers, read the notifier, call methods and assert the state. Use mocktail for mocks and keep tests fast, deterministic and independent of the network.
29

Compare Redux Toolkit, Zustand and React Context for state in React Native.

React Native Navigation, State and Native ModulesMedium
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Context is built in and fine for rarely changing values like theme or auth, but every consumer re-renders on change. Redux Toolkit gives a predictable global store with slices, middleware and excellent DevTools, suited to large teams, and RTK Query handles API caching. Zustand is small and simple, with selector-based subscriptions that limit re-renders. Server data is often better handled by TanStack Query than by any global store.
30

How would you migrate a large React Native app from JavaScript to TypeScript?

React Native Navigation, State and Native ModulesMedium
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Enable TypeScript with allowJs so both coexist, start with a relaxed tsconfig, and convert shared code first: API types, models, utilities and navigation param lists. Then convert screens feature by feature, tightening strict options gradually. Add type checks to CI so new files must be TypeScript. Avoid using any to silence errors; use unknown and narrow. Track progress and celebrate milestones to keep momentum.
31

How do you pass parameters between screens and type them safely?

React Native Navigation, State and Native ModulesEasy
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Pass small, serialisable params like IDs with navigation.navigate('Details', { id }), and read them with route.params. Define a param list type, such as type RootStackParamList = { Details: { id: string } }, and use it with the navigator and hooks for type checking. Avoid passing functions or large objects, which break state persistence and deep linking; fetch full data on the destination screen.
32

What is Maestro and why do mobile teams use it?

Testing, Performance and CI/CDMedium
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Maestro is an open-source mobile UI testing framework where flows are written in simple YAML, such as launchApp, tapOn "Login" and assertVisible "Welcome". It works with native, Flutter and React Native apps on Android and iOS, handles waiting automatically, and reduces flakiness compared to many older tools. Teams use it for smoke tests of critical journeys in CI because tests are quick to write and readable by QA.
33

What is Supabase and how does it compare to Firebase?

Mobile Backend, APIs and FirebaseMedium
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Supabase is an open-source backend platform built on PostgreSQL, offering authentication, a relational database with auto-generated APIs, row level security, storage, edge functions and real-time subscriptions. Firebase uses NoSQL databases like Firestore. Supabase suits apps with relational data and SQL needs, and can be self-hosted, while Firebase has a richer mobile ecosystem including Crashlytics, Remote Config and FCM. Many apps combine them.
34

Integration tests pass locally but fail randomly in CI. How do you make them reliable?

Testing, Performance and CI/CDMedium
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Flaky tests usually come from timing assumptions, shared state, network dependence or slow emulators. Replace fixed delays with waiting for specific conditions, mock or stub network calls with predictable responses, reset app data between tests, and use stable selectors like keys or test IDs instead of text that changes. Give CI emulators enough resources, retry only as a temporary measure, and track flaky tests separately to fix them.
35

How do you set up CI/CD for a cross-platform mobile app?

Testing, Performance and CI/CDMedium
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On every pull request, run lint, formatting checks, unit and widget or component tests. On merge, build signed Android and iOS release artifacts using CI services such as GitHub Actions, Codemagic, Bitrise or EAS Build, with signing keys stored as secrets. Use fastlane or EAS Submit to upload to internal testing tracks and TestFlight. Automate version numbers, generate release notes and run smoke tests with Maestro.
36

Write a GitHub Actions workflow that runs Flutter tests on every pull request.

Testing, Performance and CI/CDMedium
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name: flutter-ci on: pull_request: branches: [main] jobs: test: runs-on: ubuntu-latest steps: - uses: actions/checkout@v4 - uses: subosito/flutter-action@v2 with: channel: stable cache: true - run: flutter pub get - run: dart format --set-exit-if-changed . - run: flutter analyze - run: flutter test --coverage
37

What is the role of a mobile developer in an Agile team?

Mobile Development FundamentalsEasy
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A mobile developer turns user stories and designs into working app features, estimates tasks in sprint planning, raises technical risks early, and collaborates with backend, design and QA. They join standups, demos and retrospectives, review peers' code and keep builds releasable. They also give input on platform constraints like store review times and OS limits, which affect release planning more than in web development.
38

How do you handle account deletion requirements in mobile apps?

App Store and Play Store PublishingMedium
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Both major stores require apps that let users create accounts to also let them delete their account from within the app, and the Play Store also requires a web link for deletion requests. Implement a clear settings option, confirm the action, call a backend endpoint that deletes or anonymises user data according to retention rules, revoke tokens, clear local data and sign the user out. Document what is retained for legal reasons.
39

Your team has no automated tests and frequent regressions. How would you introduce testing?

Testing, Performance and CI/CDMedium
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Start where bugs hurt most: write unit tests for business logic like pricing, validation and state transitions, and a few end-to-end smoke tests for login, checkout and payment flows with Maestro or integration tests. Run them in CI on every pull request so failures block merges. Require tests for bug fixes going forward. Show reduced regressions after a few sprints to build team support.
40

How do you handle error boundaries in a React Native app?

React Native Navigation, State and Native ModulesMedium
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An error boundary is a class component, or a library like react-error-boundary, that catches rendering errors in its child tree and shows a fallback UI instead of crashing the whole app. Place one at the app root and around risky screens. They do not catch errors in event handlers or async code, so use try-catch there. Report caught errors to a crash reporting tool with context for debugging.

Frequently asked questions

What happens in the Mobile App Development technical round round?

The technical round is the core of a Mobile App Development interview: concept questions with follow-ups, a live hands-on task and a deep dive into one of your projects. Interviewers check depth, not just definitions.

How do I clear the technical round round?

Say your approach out loud before you start writing. After a correct answer, expect 'why?' and 'what if?' follow-ups; go one level deeper than the question. Pick one project you can explain end to end, including what you would do differently.

Which round comes next?

A typical order is online assessment, telephonic screening, one or two technical rounds, a managerial round and HR. Use the other round pages to practise each stage.

Practise every interview round

Online Assessment questionsTelephonic Interview questionsManagerial Round questionsRapid-Fire questionsHR & behavioural questionsFull mock interview

More ways to practise

Company-wise Mobile App Development questionsExperience-wise Mobile App Development questionsRole-wise Mobile App Development questionsCity-wise Mobile App Development questionsMost asked Mobile App Development questionsScenario-based questionsPractical / hands-on questionsHR & behavioural questionsMobile App Development mock interviewOnline assessment questionsTechnical round questionsManagerial round questionsMobile App Development topic sheets