Intermediate interview questions in Android & Kotlin, page 5
How do you upload a file with text data in Retrofit?
Tests multipart uploads versus JSON bodies. Strong answer: @Multipart, @POST, @Part; file as MultipartBody.Part and text as RequestBody; avoid @Field. Red flag: suggesting @Body with a data class.
Explain Hilt scoping: @Singleton vs @ActivityRetainedScoped
Tests Hilt component lifecycles. Answer: @Singleton lives for the app process; @ActivityRetainedScoped survives config changes via ActivityRetainedComponent but dies when the activity finishes.
How do you inject two different OkHttpClient instances with Hilt?
Tests Hilt qualifiers for same-type bindings. Answer: define a custom @Qualifier (or @Named), annotate two @Provides methods and the injection site. Red flag: manual client creation or subclassing OkHttpClient instead of qualifying the binding.
Functional difference between @Binds and @Provides in Hilt
Tests if you understand Hilt code generation tradeoffs. @Binds wires an existing injectable implementation to an interface with less overhead; @Provides constructs instances manually.
How would you access a Hilt dependency in a non-injectable ContentProvider?
Tests Hilt's escape hatch for framework classes. Strong answer: define an EntryPoint in SingletonComponent, expose the dependency, and retrieve it with EntryPointAccessors.fromApplication. Red flag: field injection or manual static singletons.
Explain Structured Concurrency in Kotlin Coroutines
Structured concurrency binds coroutines to a scope; parent cancellation propagates to all children, preventing leaks.
Unit test a ViewModel exposing StateFlow in a local JVM test
Tests coroutine hygiene and flow collection strategy. A strong answer covers injecting a TestDispatcher, using runTest, collecting emissions in a background scope, and asserting states.
Explain integration tests and isolate Room DAO tests
Tests integration vs unit testing and Room isolation. Outline: verify real DAO-to-DB interaction with Room.inMemoryDatabaseBuilder; reset state by closing and recreating the DB in @After. Red flag: mocking the DAO or using an on-disk database.
Mock vs Fake test doubles: when to use a Fake Repository?
Tests if you know a Fake is a working lightweight implementation while a Mock verifies interactions. Good answers define Fake as in-memory with real logic, Mock as expectation-based, and choose a Repository Fake when many tests need reusable state.
How do you test a Compose click and verify state change?
This tests Compose semantics and interaction-to-assertion flow. Mention ComposeTestRule, onNodeWithTag, performClick, and assert on the changed node with assertIsDisplayed or assertTextEquals.
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.
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.
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.
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.
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.
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.
What are RecyclerView.Adapter and ViewHolder, and why do they improve scrolling?
This tests RecyclerView's data-to-view separation. A strong answer says Adapter binds data while ViewHolder caches findViewById results, avoiding hierarchy scans on scroll. A red flag is calling ViewHolder a memory saver instead of a lookup cache.
How do include, merge, and ViewStub optimize deep layout nesting?
This tests Android view inflation and hierarchy flattening. A strong answer covers include for reuse, merge to strip redundant parents during inflation, and ViewStub for lazy-loading heavy views. A red flag is conflating them or citing XML brevity alone.
Explain touch event dispatch in a ViewGroup with a clickable child
It tests touch routing through the three key methods. A strong answer traces ACTION_DOWN from root to target, notes intercepting halts child delivery, and onTouchEvent true consumes while false bubbles up.
How do you diagnose and optimize a slow Room query?
Tests SQLite profiling and Room optimization. Isolate the query with Database Inspector, run EXPLAIN QUERY PLAN to spot scans, then add covering indexes, rewrite joins, or use Paging3. Red flag: blindly adding indexes or switching to NoSQL without measuring.
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