Intermediate everything in Mobile Dev, page 19
When and why to use a Foreground Service?
Tests your grasp of Android's background execution limits. A great answer explains they're for user-visible tasks like music playback, requires startForegroundService(), and must show a notification within 5 seconds.
Describe the back stack for A -> B -> C with singleTask
Tests understanding of the singleTask launch mode. A great answer explains that launching C destroys B, as singleTask clears all activities above it in the task. The final back stack becomes [A, C]. A red flag is confusing this with singleTop.
How does a ViewModel survive configuration changes?
Tests understanding of lifecycle-aware components. ViewModels are retained by a ViewModelStore owned by the Activity/Fragment, which survives configuration changes. The ViewModel is cleared only when its scope is permanently finished.
What is ADB and what are two common commands you use?
Tests your hands-on familiarity with the core Android toolchain. Define ADB's client-server architecture, then explain adb install for APKs and adb logcat for logs. A red flag is being unable to name specific commands or only knowing IDE buttons.
Which tool inspects the view hierarchy to debug layouts?
This tests your knowledge of core Android Studio debugging tools. A great answer names the Layout Inspector, describes its 3D component tree and attributes pane, and notes its live update capability on API 29+. A red flag is only mentioning XML files.
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.
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.
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.
What is a CoroutineDispatcher and when do you use each type?
Tests your grasp of coroutine threading. A dispatcher manages which threads a coroutine runs on. Explain Main for UI, Default for CPU-intensive work, and IO for blocking operations. A red flag is mixing up IO and Default or using Unconfined.
Hot vs. Cold Streams: `StateFlow` vs. `Flow`
Tests your grasp of stream lifecycles. A great answer defines cold Flow (lazy, per-collector) vs. hot StateFlow (shared, active), then uses a ViewModel UI state scenario to show why StateFlow is correct for surviving configuration changes.
Structured Concurrency in Kotlin Coroutines
Tests your understanding of coroutine lifecycles and error handling. A good answer defines the parent-child relationship, then explains how cancellation and exceptions propagate through the scope. A red flag is simply calling it a way to 'group' coroutines.
Explain and implement a higher-order function in Kotlin
Tests your grasp of functions as first-class citizens. Define a higher-order function, explain it takes/returns functions, then implement filterAndTransform using the specified lambdas.
lateinit var vs. val by lazy in Android
Tests your grasp of Kotlin's non-nullable property initialization. Define lateinit (mutable, framework-init) vs. lazy (immutable, deferred-init). Use lateinit for Views in onCreate and lazy for expensive objects. Red flag: confusing their mutability.
What are the advantages of a Kotlin data class?
Tests knowledge of Kotlin's boilerplate reduction for data holders. A good answer defines the advantage (conciseness), names generated functions like equals, hashCode, and copy, and explains copy for immutable state updates.
What is a Kotlin extension function? Write one for String.
Tests your grasp of adding functionality to existing classes without inheritance. A great answer defines it as syntactic sugar over static methods, explains its use for third-party code, then implements the requested String.hasWhitespace function.
Why is `LiveData<Boolean>` bad for one-time ViewModel events?
This tests your grasp of state vs. events. A LiveData<Boolean> is state; it re-triggers on rotation. Instead, expose events via a StateFlow and have the UI call an eventConsumed() function on the ViewModel to maintain unidirectional data flow.
Implement an efficient list in Jetpack Compose
Tests your grasp of UI virtualization in Compose. Answer: Use LazyColumn as it only composes visible items. Contrast this with Column, which composes all items at once, causing poor performance. Mention the items DSL.
Which side-effect handler for a one-time coroutine action in Compose?
This tests your understanding of Compose lifecycles and side-effect handlers. A good answer names LaunchedEffect(Unit), explaining the constant key ensures the effect runs only once. A red flag is suggesting launching coroutines on every recomposition.
Describe state hoisting in Jetpack Compose.
Tests your grasp of unidirectional data flow. Explain state hoisting is moving state up to make composables stateless. This improves reusability, testability, and creates a single source of truth. A red flag is defining it without explaining the benefits.
Explain Recomposition in Jetpack Compose
Tests your grasp of Compose's declarative model. A good answer defines recomposition, explains state-read triggers, and details how stability and positional memoization enable skipping. A red flag is assuming any state change redraws the entire UI.
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