74 Mobile Essentials interview questions with answers

All Mobile Essentials interview questions

• What is a `Future` in Dart and how is it different from a `Stream`?

• What is the difference between `StatelessWidget` and `StatefulWidget`?

• What is `BuildContext` and why is it important?

• Explain the widget tree, element tree, and render tree in Flutter.

• What is the purpose of widget `Key`s and when should you use them?

• What is `const` constructor and why is it important for Flutter performance?

• What is `setState()` and why does calling it trigger a rebuild?

• Explain the BLoC pattern and why interviewers ask about it.

• Compare Provider, Riverpod, and BLoC: when would you use each?

• What is the difference between the old `Navigator` (v1) and modern routing approaches?

• What is clean architecture and why is it important for large apps?

• What are isolates in Dart and when do you use them?

• What are platform channels and when do you use them?

• How do you test Flutter apps? What's the difference between unit, widget, and integration tests?

• What are suspend functions in Kotlin?

• Explain the Android Activity lifecycle and each method's purpose.

• What are Intents in Android and what are the two types?

• What is a Service in Android and when should you use it?

• What are the different Android permission types and how do you handle runtime permissions?

• Explain state management in Jetpack Compose using `mutableStateOf` and `remember`.

• What is MVVM architecture and how is it structured?

• Explain the difference between LiveData and StateFlow.

• What is a ViewModel and why should you use it?

• What is Room database and why use it instead of SQLite directly?

• What are Interceptors in Retrofit/OkHttp and how do you use them?

• What is certificate pinning and how do you implement it?

• What is Hermes and how is it different from JSC?

• Fundamental differences — RN vs Flutter vs native (Swift/Kotlin) for new 2026 projects?

• How does Flexbox in RN differ from CSS on the web?

• react-navigation v7 — when to use Stack vs Tab vs Drawer?

• How does FlatList stay smooth with 10k items? How to tune `windowSize`/`maxToRenderPerBatch`/`getItemLayout`?

• `useCallback` / `useMemo` in RN — when do you really need them?

• What is the New Architecture, what does it include, and from which RN version is it default?

• What is JSI, and how is its native call mechanism different from the old Bridge?

• TurboModules vs old NativeModules — concrete differences?

• Animated API vs Reanimated — which one should you use?

• App size optimization — ProGuard/R8, Hermes, ABI splits, asset compression?

• Push notifications — FCM + APNs, Expo Notifications, how to set up?

• What is the difference between hot reload and hot restart?

• How does Flutter store data locally and when do you use which option?

• What is a Fragment and how does its lifecycle differ from an Activity?

• What is recomposition in Jetpack Compose?

• What problem does the Jetpack Navigation Component solve?

• How are hooks used in React Native and how do useState and useEffect differ?

• Why do React Native apps jank, and how do the JS thread and UI thread differ?

• What is the mobile app lifecycle (foreground/background) and how does React Native track it?

• How should you handle API integration and caching in a mobile app?

• What is deep linking, and how do custom schemes, App Links and Universal Links differ?

• What is code signing when releasing an app, and why is it needed?

• How do responsive and adaptive UI differ in mobile?

• What matters when optimizing memory and battery for a mobile app?

• What is offline-first architecture and how do you handle sync and conflicts?

• What are the essentials of storing sensitive data and basic mobile security?

• What is the difference between `lateinit` and `by lazy` in Kotlin?

• How do native, hybrid and cross-platform apps differ?

• What is the difference between `versionCode` and `versionName` when releasing an app?

• What are flavors in Flutter and what are they used for?

• A countdown timer (OTP, payment hold) drifts when the app goes to the background — how do you handle it?

• How does background work (sync, uploads) differ between iOS and Android, and how should a cross-platform app handle it?

• How do you protect a mobile app against reverse engineering and tampering?

• How do you track crashes of an app in production?

• The OS kills the app while it is in the background and the user comes back to find their input gone — how do you handle it?

• What are the steps to publish an app to Google Play and the App Store?

• The access token expires while many requests run in parallel — how do you refresh it without firing multiple refresh calls?

• The app works in debug but crashes or shows a white screen in release — how do you debug it?

• How do you integrate biometric login (fingerprint, Face ID) securely?

• When should an app use a WebView, and how do web and native communicate safely?

• A list with many images makes memory keep climbing and the app stutter — how do you fix it?

• How do you design uploading large photos/videos over an unstable network?

• What is `Context` in Android? Contrast Application context vs Activity context (memory-leak angle).

• What is an ANR (Application Not Responding) and how do you prevent it?

• What is `RecyclerView` and how does its view-recycling mechanism work?

• Distinguish cold / warm / hot start and how to optimize app startup time.

• What is `InheritedWidget` and how does it pass state down the widget tree? (the foundation of Provider)