Interview questions in Mobile Dev, page 28
The dynamic keyword and message dispatch
Dynamic forces Objective-C message dispatch via objc_msgSend, enabling KVO and swizzling, at the cost of skipping inlining and devirtualization.
Flutter's Widget, Element, and RenderObject trees: roles and relationships
Tests your mental model of Flutter's rendering layers. Strong answer: Widget is immutable configuration; Element is the mutable lifecycle manager owning the RenderObject; RenderObject is the concrete layout and paint entity.
How would you use Perfetto and Trace.beginSection to find a non-obvious bottleneck?
Tests correlation beyond CPU sampling. Covers coarse Trace.beginSection to limit 1-10us overhead, recording app ATrace with CPU/scheduling tracks, and correlating slices against scheduler latency. Red flag: omitting overhead or ignoring Perfetto SQL queries.
Limits of OTA Updates and Runtime Versions
OTA ships only JS and assets; native changes need a store build; runtime versions gate compatibility.
Verifying and avoiding copy-on-write overhead
Confirm extra copies via isKnownUniquelyReferenced or instruments and the retain trace; ensure unique references, mutate inout/in place, reserveCapacity, avoid aliasing.
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.
Purpose of Android app signing and keystore contents
Signing proves authorship and integrity, enables same-key updates, and binds app identity; a keystore holds private keys and certificates.
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.
Debugging a closure capture leak in a third-party library
Use the Memory Graph Debugger to inspect retain paths, the Leaks and Allocations instruments, and malloc stack logging; trace the cycle before patching.
Isolating and reducing excessive widget rebuilds
Push state down, use const subtrees, rebuild only listeners with ValueListenableBuilder, isolate repaints with RepaintBoundary.
What is an Android App Bundle and its advantages over APK?
Tests knowledge of modern Play distribution. AAB is the publishing format with all code and resources; Play generates device-specific APKs for smaller downloads and supports dynamic features. Red flag: calling it a compressed APK or ignoring dynamic delivery.
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.
Copy-on-write and implementing it for a custom struct
CoW shares a buffer until mutation, deep-copying only when the buffer is non-unique; Array, Dictionary, Set, String use it; implement with a class storage box and isKnownUniquelyReferenced.
Explain 'constraints go down, sizes go up, parent sets position.'
Tests Flutter layout protocol and unbounded width errors. Strong answers trace how a child gets infinite width from a scrolling parent and fix it with a bounded wrapper. Red flag: blaming the child without tracing parent constraints.
Google Play App Signing: upload key versus app signing key
Tests Android signing infrastructure and key escrow knowledge. A strong answer states Google holds the app signing key while you retain an upload key, protecting critical signing material. Red flag: claiming both keys sign the final install artifact.
Debouncing a Search TextInput with Hooks
Keep input in state, in an effect set a timer that fires the search after a delay, clear the timer on each change so only the final pause triggers the call.
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