Intermediate interview questions in Mobile Dev, page 12
Diagnose Android UI jank using Android Studio's Profiler
Start with CPU Profiler for traces over 16ms and main thread blocking; check Memory Profiler for GC.
Android App Bundles versus Universal APKs
An AAB is an upload format; Play generates per-device APKs via dynamic delivery, shrinking download size.
Struct versus class performance and memory tradeoffs
Structs are value types, often stack-allocated with no ARC; classes are heap-allocated reference types with retain counts.
Walk me through a Flutter CI/CD pipeline for Play Store and TestFlight
Tests your ability to orchestrate multi-platform Flutter builds, manage signing secrets, and automate deployments to Google Play Internal Testing and Apple TestFlight.
Explain cold, warm, and hot app startups and three cold-start optimizations
Cold means no process; warm means process lives but activity recreates; hot means activity resumes. Three fixes: lazy-load deps, trim Application.onCreate, defer blocking I/O.
Over-the-Air Updates for JavaScript-Only Fixes
Ship a new JS bundle the app downloads at runtime and applies on next launch, with no store review.
Exposing Swift classes to Objective-C
Subclass NSObject or mark members @objc, import the generated ModuleName-Swift.h, and accept that Swift-only types like enums with associated values cannot cross.
How do you handle platform-specific configurations per flavor on Android and iOS?
Tests if you know flavors delegate icons and titles to native tooling. On Android, use productFlavors in build.gradle with source sets or placeholders; on iOS, use Xcode build configurations with Info.plist values or asset catalogs.
What is certificate pinning and what are its trade-offs?
Pinning hardcodes a server key to block rogue CA MITM; trade-offs are breakage on cert rotation and forced updates.
CI/CD Pipeline for React Native to TestFlight and Play
A triggered workflow installs deps, builds signed artifacts on macOS and Linux runners, uploads via Fastlane to TestFlight and the Play internal track.
What an autoreleasepool is and when to add one manually
An autorelease pool holds objects until it drains; wrap tight loops creating many temporary ObjC objects in autoreleasepool to cap peak memory.
dispatch_async versus Task.detached for offloading work
Dispatch_async submits a closure to a queue; Task.detached starts an unstructured async task off the current actor without inheriting context.
Walk me through Flutter's rendering pipeline and its phases.
Tests your understanding of the three-tree separation and how changes become pixels. Outline: setState marks objects dirty; Build updates elements, Layout computes sizes bottom-up via constraints, and Paint records commands top-down into layers.
StyleSheet.create and Inline Style Tradeoffs
Styles are JS objects of subset-CSS properties; StyleSheet.create validates them and yields stable references, while inline objects allocate each render.
Isolating and reducing excessive widget rebuilds
Push state down, use const subtrees, rebuild only listeners with ValueListenableBuilder, isolate repaints with RepaintBoundary.
JSI, Fabric, and TurboModules in the New Architecture
JSI gives JS direct synchronous access to native via C++, Fabric is the new renderer, TurboModules lazy-load native modules.
map versus compactMap versus flatMap
Map transforms each element one-to-one; compactMap transforms then drops nils; flatMap transforms to sequences then concatenates.
Which DevTools view diagnoses janky Flutter animations?
Open Performance view; compare UI and Raster bars; flag bars over 16ms; blame UI bloat on builds and Raster jank on shaders or saveLayer.
Release build ClassNotFoundException not in debug: cause and file?
Tests R8 shrinking awareness: release-only obfuscation removes classes loaded by reflection. Check proguard-rules.pro first and add a -keep rule. Red flag: blaming multidex or disabling minification rather than writing a targeted keep rule.
Responsive Layouts with Core React Native APIs
Lean on flexbox, percentage sizing, useWindowDimensions, SafeAreaView, and Platform; recompute on dimension change.
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