More in Mobile Dev — page 26
Tree Shaking Removes Unused Flutter Code
Tree shaking is the compiler deleting code your app never calls, so importing a massive package only costs the pieces you use. It runs automatically in release builds. Relying on dynamic dispatch or dart:mirrors silently disables it and brings back the bloat.
Legacy Integration Testing with flutter_driver
flutter_driver remotely pilots your app from a host via Dart VM service, common in legacy codebases with host-side scripts. Do not treat it as an in-process widget test because it runs outside the app; you cannot inspect state or use flutter_test matchers.
Repository Pattern: Hide Your Data Sources
A repository is a contract that hides where your data lives. Your Flutter app should not care if a user profile comes from Firebase, SQLite, or a mock. Engineers often leak HTTP clients or database models into UI instead of returning domain models.
Flutter Network Errors: Fail Gracefully
Treat every network call as a promise that might break. In Flutter, catch exceptions at the HTTP boundary and map them to UI states like retry widgets. The footgun is letting Dio or http exceptions bubble up, crashing the app instead of degrading gracefully.
Full-Text Search in Local Flutter Databases
SQLite FTS5 is an inverted index in your app: words map to row IDs, skipping brute-force scans. Use it when local tables exceed thousands of rows and LIKE lags. The footgun is that FTS virtual tables never auto-sync, so stale indexes return wrong rows.
Passing Arguments to Flutter Named Routes
Flutter named routes pass data through an arguments field instead of global variables. Use this when navigating to a route that needs an ID or configuration object. Arguments are untyped by default, so unsafe casts crash at runtime.
Explain R8's shrinking, obfuscation, and optimization phases and how to influence optimization
WHAT IT TESTS: Whether you understand R8 beyond a black box. ANSWER OUTLINE: Separate dead code removal, renaming, and bytecode transformation; cite ProGuard keep rules and selective passes. RED FLAG: Thinking optimization is only the minifyEnabled toggle.
Describe staged rollout on Google Play Console, benefits, and metrics to monitor
Tests release engineering and risk mitigation. Covers: set percentage and countries, manually ramp, halt on bad signals; benefits are blast-radius reduction and real-world validation. Flag: auto-ramping claims or ignoring halted users keep the bad build.
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.
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.
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.
Purpose of Android app signing and keystore contents
WHAT IT TESTS: App identity on Android. ANSWER OUTLINE: Signing proves authorship and integrity, enables same-key updates, and binds app identity; a keystore holds private keys and certificates.
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.
Explain generational GC in ART and why onDraw must avoid allocations
WHAT IT TESTS: ART generational GC and onDraw allocation hazards. ANSWER OUTLINE: Covers young-gen nursery, mark-sweep fallback, and why a 5-10ms GC pause misses 16ms frame deadline. RED FLAG: Blaming GC without linking allocation to frame timing.
Use Android Keystore to secure a database encryption key
Tests Android Keystore key generation and hardware trust boundaries. Strong answers: KeyGenParameterSpec with AES/GCM, TEE vs StrongBox isolation, setIsStrongBoxBacked on API 28+ with fallback, wrapping the database key. Red flag: claims Keystore encrypts DBs.
What is certificate pinning and what are its trade-offs?
WHAT IT TESTS: Understanding TLS trust chain attacks beyond HTTPS. ANSWER OUTLINE: Pinning hardcodes a server key to block rogue CA MITM; trade-offs are breakage on cert rotation and forced updates.
Explain cold, warm, and hot app startups and three cold-start optimizations
WHAT IT TESTS: App startup modes and tuning tactics. ANSWER OUTLINE: 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.
Diagnose Android UI jank using Android Studio's Profiler
WHAT IT TESTS: Isolating frame drops to main thread work or GC via Android Studio Profiler. ANSWER OUTLINE: Start with CPU Profiler for traces over 16ms and main thread blocking; check Memory Profiler for GC. RED FLAG: Using Logcat alone or blaming hardware.
Why avoid plain SharedPreferences for secrets and what to use?
Tests data-at-rest security awareness. A strong answer notes plain SharedPreferences writes unencrypted XML that rooted users or backups expose, then names EncryptedSharedPreferences with Android Keystore.
What is overdraw in Android UI and how do you reduce it?
This tests GPU fill awareness. A strong answer defines overdraw as redrawing pixels repeatedly, names Debug GPU Overdraw's color overlay, and offers fixes: remove unnecessary backgrounds and flatten hierarchies. Red flag: confusing this with CPU layout issues.