Intermediate interview questions in Mobile Dev, page 3
Explain Kotlin's declaration-site variance with in and out
Out T means covariant producer (read), in T means contravariant consumer (write), removing wildcard noise.
Explain Kotlin's declaration-site variance with `in` and `out`
This tests your grasp of type systems and API design. Explain how out (covariance/producer) and in (contravariance/consumer) provide type safety at the declaration site, simplifying usage. A red flag is confusing variance with immutability.
Explain Kotlin's declaration-site variance with in and out
This tests your grasp of generic type safety and API design. Explain that out marks covariant producers (e.g., List<out E>) and in marks contravariant consumers, then contrast this cleaner declaration-site model with Java's repetitive use-site wildcards.
keyboardShouldPersistTaps in ScrollView
KeyboardShouldPersistTaps controls whether taps dismiss the keyboard or reach children; values never, always, and handled.
Explain symbolic breakpoints and debug Auto Layout with one
Tests debugging closed-source frameworks without source lines. A strong answer says a symbolic breakpoint stops on UIViewAlertForUnsatisfiableConstraints, then checks the backtrace or log to find the bad view.
Which Instrument diagnoses scroll stuttering and dropped frames?
Tests whether you connect UI jank to Instruments data. A strong answer names the Core Animation or Time Profiler instrument, cites frame duration and hitch ratio, and correlates spikes with main-thread work.
Describe the Dart event loop and queue execution order
Tests your grasp of Dart's single-threaded event loop priority. Great answers state: microtasks drain fully before the next event processes, cycling forever. Red flag: saying Future and scheduleMicrotask interleave in call order.
Explain single-subscription vs broadcast Streams in Dart
Tests dart:async stream lifecycle. Outline: single-subscription allows one listener and emits on listen; broadcast supports many but drops events for late arrivals. Red flag: saying single-subscription allows multiple listeners or buffers events.
Structuring an auth flow in React Navigation
Conditionally render an auth stack versus app stack from state, not navigate calls; store token; let state drive screens.
Fetch user profiles concurrently and handle individual failures
Tests Future.wait concurrency and per-future error isolation. Answer: map IDs to fetchProfile, pass to Future.wait. For partial failures, attach catchError per future to return null, then filter. Red flag: try-catch around Future.wait or sequential awaits.
Refetching data when a screen gains focus
Use useFocusEffect with a useCallback callback; refetch on focus; clean up to abort stale requests.
Accessing navigation outside a screen component
Use the useNavigation hook inside any component under NavigationContainer; for navigating outside React, use a navigationRef.
Setting screen options statically versus dynamically
Options prop on Screen (can read route) versus navigation.setOptions inside the screen for state-driven changes.
App crash: debug with Logcat and breakpoints in Android Studio
This tests systematic debugging and Android Studio fluency. A strong answer reproduces the crash, filters Logcat for the fatal exception, sets a breakpoint on the offending frame, and inspects variables.
How would you debug an app crash in Android Studio?
This tests your systematic debugging process. A good answer starts with Logcat to find the stack trace, then uses breakpoints to inspect program state *before* the crash occurs. A red flag is randomly adding print statements instead of using the debugger.
How do you debug an app crash in Android Studio?
Tests your systematic problem-solving process. A great answer outlines reproducing the crash, analyzing the Logcat stack trace for the FATAL EXCEPTION, and then using strategic breakpoints and the variable inspector to find the root cause of the bad state.
How do UITableView and UICollectionView reuse cells?
This tests your understanding of UIKit's flyweight pattern and scroll performance. A strong answer covers the reuse pool, dequeueReusableCell mapping identifiers to new index paths, and registration.
Relationship between Widget, Element, and RenderObject trees and their benefits
Widget configures, Element owns state, RenderObject paints; Element.update reuses the RenderObject, so rebuilds stay cheap.
Explain what a Gradle product flavor is and give a free vs pro example
Tests understanding of build-variant dimensions beyond build types. A strong answer defines flavorDimensions, sets free and pro applicationIdSuffix values, and explains variant generation. Red flag: conflating flavors with build types or manual APK renaming.
What is a Gradle product flavor?
This tests your understanding of build variants beyond debug/release. Define flavors for user-facing versions (free/pro), contrast with build types, and configure with applicationIdSuffix and buildConfigField.
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