Mobile App Development Interview Questions for Freshers
40 questions with answers for candidates with Freshers — 26 easy, 14 medium.
What interviewers expect: freshers
Fresher interviews cover programming basics, Dart or JavaScript fundamentals, simple widgets or components, state with setState or useState, and calling an API. Expect a short live coding task like building a list screen and detailed questions on your projects. Interviewers want to see that you built and ideally published an app yourself and can explain each part of it.
This set is weighted towards Dart and Flutter Basics (8), React Native Core (7), React Native Navigation, State and Native Modules (7), Mobile Development Fundamentals (7).
Dart or JavaScript fundamentals Basic widgets or components API calls and JSON parsing One published portfolio app
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01
What is Firebase and which services do mobile apps commonly use?
Firebase is a mobile and web development platform. Commonly used services are Authentication for email, phone OTP and social logins; Cloud Firestore and Realtime Database for synced data; Cloud Storage for files; Cloud Functions for server code; Cloud Messaging for push notifications; Crashlytics for crash reports; Analytics; Remote Config for feature flags; and App Distribution for testers. FlutterFire and React Native Firebase provide SDKs.
02
What is the difference between StatelessWidget and StatefulWidget?
A StatelessWidget has no mutable state; its build output depends only on constructor parameters and inherited data. A StatefulWidget creates a State object that persists across rebuilds and holds mutable data; calling setState marks it dirty so build runs again. Use stateful widgets for local UI state like animations, text controllers or toggles, and lift shared or business state into a state management solution.
03
Explain Row, Column, Expanded and Flexible in Flutter layouts.
Row lays out children horizontally and Column vertically, with mainAxisAlignment and crossAxisAlignment controlling placement. Expanded forces a child to fill remaining space along the main axis, and Flexible lets a child take up to its share but be smaller. Using flex values divides space proportionally. A common error is an unbounded width or height, such as a ListView inside a Column without Expanded, which throws a layout exception.
A Future represents a value that will be available later, like an HTTP response. Marking a function async lets it use await, which pauses that function until the Future completes without blocking the event loop. Errors are handled with try-catch. Dart runs on a single-threaded event loop per isolate, so awaiting network calls keeps the UI responsive. Use Future.wait to run independent futures concurrently.
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.
React Native lets you build mobile apps with React and JavaScript or TypeScript. You write components like View, Text and Image, and React Native renders them as real native views on Android and iOS. JavaScript runs on the Hermes engine, and with the New Architecture it communicates with native code directly through JSI rather than an asynchronous JSON bridge. Business logic and most UI code are shared between platforms.
Use Jest as the test runner with React Native Testing Library, which renders components and queries them the way users do, by text, role or label. Fire events like fireEvent.press or userEvent, then assert on output. Mock native modules and network calls with jest mocks or MSW. For end-to-end tests on real builds, use Detox or Maestro, which drive the app on emulators and simulators.
Since Dart 3, all code is null safe. Types are non-nullable by default, so String cannot hold null while String? can. The compiler forces you to handle nulls with checks, the ?. and ?? operators, or the ! operator which throws if null. The late keyword declares a non-null variable initialised later. Sound means the compiler can trust non-null types completely, enabling optimisations and preventing many runtime null errors.
09
Why do Flutter apps need a state management solution beyond setState?
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.
10
What is the difference between final and const in Dart?
final means a variable is assigned once at runtime and cannot be reassigned. const means the value is a compile-time constant and deeply immutable. In Flutter, const constructors like const Text("Hello") let the framework reuse the same widget instance across rebuilds, skipping unnecessary work. Use const wherever possible for widgets with fixed values; the linter rule prefer_const_constructors helps enforce it.
11
What are the steps to publish an iOS app on the App Store?
Enrol in the developer program, create an App ID and the app record in App Store Connect, and set up signing with certificates and provisioning profiles, often managed automatically by Xcode or EAS. Archive the release build with an incremented build number, upload it, and test through TestFlight. Complete metadata, screenshots, privacy nutrition labels and age rating, then submit for review. After approval, release manually, automatically or in phased release.
12
Parsing a 10 MB JSON file freezes the Flutter UI for two seconds. How do you fix it?
JSON decoding is CPU-bound and runs on the main isolate, blocking frames. Move it to a background isolate with Isolate.run(() => parseProducts(jsonString)) or compute. Also consider whether the API can paginate or return less data, and parse lazily. Test in profile mode with DevTools performance view to confirm the frame time improvement, since debug mode exaggerates slowness.
13
How does navigation work in React Native with React Navigation?
React Navigation provides navigators: native stack for push and pop screens using platform transitions, bottom tabs, drawer and material top tabs. You nest navigators, for example tabs inside a root stack with modal screens. Screens receive navigation and route props or use hooks like useNavigation and useRoute. Version 7 adds a static configuration API for better TypeScript inference and automatic deep link setup.
14
Write a React Native Testing Library test for a login button showing a validation error.
I test the happy path and edge cases myself on both Android and iOS, including no network, slow network, empty states, large text sizes and rotation. I write unit tests for logic and run the existing test suite. I review my own diff before raising the pull request and add clear testing notes for QA explaining what changed and what to check, which saves time for both of us.
16
How do you monitor crashes and performance in production?
Integrate a crash reporting tool like Firebase Crashlytics or Sentry, upload debug symbols, dSYMs and source maps so stack traces are readable, and record non-fatal errors with context. Track crash-free users, ANR rate, app start time, slow frames and network latency per release. Set alerts on spikes and review store vitals. Tag events with app version, device and OS so problems can be isolated quickly.
17
How do you pass parameters between screens and type them safely?
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.
18
What are runtime permissions and how do they differ between platforms?
Both platforms require runtime approval for sensitive features like camera, location, contacts and notifications. Android requires declarations in AndroidManifest.xml and runtime requests for dangerous permissions; iOS requires usage description strings in Info.plist, and the app crashes if a description is missing when requesting. iOS allows asking only once; later the user must change settings. Plugins like permission_handler or react-native-permissions unify the API.
19
Write a Flutter widget test that taps a button and checks the counter text.
Conditionally render screen groups based on auth state: if the user is signed out, the navigator shows login and signup; when signed in, it shows the app screens. Changing state automatically switches stacks and prevents going back to login with the back button. Restore tokens from secure storage on startup while showing a splash screen. Expo Router offers protected routes for the same pattern.
21
Describe a time you had to deliver a feature with incomplete requirements.
Situation: product asked for a referral feature with only a one-line description. Task: deliver in a sprint. Action: I listed open questions, met the product manager for 20 minutes to agree on core rules, built the agreed version with configurable reward values from the backend, and documented assumptions in the ticket. Result: we shipped on time, and later changes needed only config updates instead of a new release.
22
Your app works on Android but crashes immediately on iOS when the user taps the camera button. What is the likely cause?
The most common cause is a missing NSCameraUsageDescription key in Info.plist. iOS terminates the app when it requests a protected resource without a usage description string. Add descriptions for camera, photo library, microphone and location as required by the plugin, written clearly for the user. Also verify the plugin's iOS setup steps, run pod install, and test on a real device since simulators lack cameras.
Expo Router is a file-based router built on React Navigation. Files in the app directory become routes, so app/product/[id].tsx maps to /product/42. Layout files define stacks and tabs, and every screen is deep-linkable automatically on mobile and web. It supports typed routes, protected routes for auth, and API routes. It reduces navigation boilerplate and makes URL-based linking consistent across platforms.
24
What is the difference between ListView and ListView.builder?
The default ListView constructor builds all children at once, which is fine for a few items. ListView.builder builds items lazily as they scroll into view, using itemBuilder and itemCount, so it handles long or infinite lists efficiently. For mixed scrolling content like headers, grids and lists together, use CustomScrollView with slivers. For large lists, also set item extent or use prototypeItem to improve scroll performance.
25
What is hot reload and how is it different from hot restart?
Hot reload injects changed code into the running app and rebuilds the UI while keeping the current state, so you see changes in about a second. Hot restart reloads the whole app code and resets state, needed when changing initialisation logic, global variables or app startup. React Native offers Fast Refresh, similar to hot reload. Native code changes, such as new plugins or platform files, require a full rebuild.
26
When would you choose a cross-platform framework over native development?
Choose cross-platform when you need both Android and iOS quickly with a small team, the app is mostly forms, lists, content and API-driven screens, and design consistency across platforms is desired. Choose native when the app needs heavy graphics, deep hardware integration, advanced background processing, newest platform features on day one, or very tight performance. Many companies mix both, using native modules inside a cross-platform app.
27
How do you handle error boundaries in a React Native app?
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.
28
What are the steps to publish an app on the Play Store?
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.
29
What is the difference between ScrollView and FlatList?
ScrollView renders all its children at once, which is fine for short content but uses lots of memory and slows rendering for long lists. FlatList virtualises, rendering only items near the viewport and recycling as you scroll, with props like keyExtractor, initialNumToRender and windowSize. For very large or complex lists, FlashList offers better recycling and performance. Never nest a FlatList inside a ScrollView of the same direction.
30
Write a custom hook that fetches data with loading and error states.
Use React Native DevTools, the default debugger since 0.76, for console logs, breakpoints, React component inspection and profiling. Inspect network requests with the network panel or a proxy. For native crashes, check Logcat in Android Studio and the Xcode console. Use the performance monitor overlay for frame rates, and add a crash reporting tool like Sentry or Crashlytics for production errors with source maps uploaded.
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.
33
Write a React Native component that requests location permission and shows the coordinates using Expo.
Answer with genuine motivation and proof. For example: I enjoy building things people use every day in their pocket, and mobile gives fast feedback from real users. I started by building an attendance app for my college, published it for classmates, and improved it from their reviews. That experience of seeing ratings and usage grow made me choose mobile development as my career.
35
How do you stay productive when working with both Android and iOS platforms?
I test every feature on one Android device and one iPhone or simulator before raising a pull request, keep a checklist of common platform differences like permissions, keyboard and safe areas, and use CI builds for both platforms on each merge. I learn basic Kotlin and Swift so I can read native errors and logs. This avoids late surprises when QA tests the second platform.
36
How does token-based authentication work in mobile apps?
The user signs in and the server returns a short-lived access token, often a JWT, and a longer-lived refresh token. The app stores them securely in Keychain or Keystore-backed storage and sends the access token in the Authorization header. When it expires, the app uses the refresh token to get a new one, retrying the failed request. On logout, tokens are deleted and ideally revoked on the server.
37
Explain the mobile app lifecycle states on Android and iOS.
Both platforms move apps between foreground active, inactive, background and terminated states. On iOS, an app goes inactive during interruptions like calls, then background, where it gets limited time before suspension. On Android, activities move through resumed, paused and stopped, and the process can be killed in background. Cross-platform apps observe these through AppLifecycleListener in Flutter or AppState in React Native to pause work and save data.
38
How do you persist state in React Native between app launches?
For small key-value data use AsyncStorage or MMKV, which is much faster and synchronous. Persist Redux with redux-persist or Zustand with its persist middleware, choosing only the slices that need it. Store tokens in secure storage like expo-secure-store or Keychain and Keystore wrappers, never in plain storage. For larger structured data use SQLite through expo-sqlite or an ORM like WatermelonDB.
39
What are the main differences between Android and iOS that a cross-platform developer must know?
Navigation patterns differ: Android has a system back gesture while iOS relies on swipe-back and navigation bars. Permissions, notification setup, background execution limits, file systems and store review rules differ. iOS builds require a Mac and Xcode, with signing through certificates and provisioning profiles. Design guidelines differ between Material Design and Human Interface Guidelines, so good cross-platform apps adapt some UI per platform.
40
Write a Dart model class with fromJson and toJson.
class Product {
const Product({required this.id, required this.name, required this.price});
final String id;
final String name;
final double price;
factory Product.fromJson(Map<String, dynamic> json) => Product(
id: json['id'] as String,
name: json['name'] as String,
price: (json['price'] as num).toDouble(),
);
Map<String, dynamic> toJson() => {'id': id, 'name': name, 'price': price};
}
// For larger apps use json_serializable or freezed to generate this.
Frequently asked questions
What is asked in Mobile App Development interviews for Freshers?
Fresher interviews cover programming basics, Dart or JavaScript fundamentals, simple widgets or components, state with setState or useState, and calling an API. Expect a short live coding task like building a list screen and detailed questions on your projects. Interviewers want to see that you built and ideally published an app yourself and can explain each part of it.
How many questions should I practise before a Mobile App Development interview?
Work through all 40 questions here, then the company-wise sets for the employers you are targeting. Quality matters more than count: be able to explain why each answer is right.
Which topics matter most for Freshers?
Focus first on Dart or JavaScript fundamentals, Basic widgets or components, API calls and JSON parsing, One published portfolio app.