📱 Mobile Dev

What happens to a bound service during config changes and multiple clients?

Tests bound service reference counting. Config change destroys the Activity binding; if no other clients exist, the service stops. Multiple clients keep it alive until the last unbind. Red flag: assuming the service survives config changes without a rebind.

Your app is killed for memory; what runs when the user returns?

Tests process death versus config change. Answer: no callback on kill; return runs onCreate with savedInstanceState, onStart, and onResume. ViewModels die in process death; use SavedStateHandle. Red flag: claiming onDestroy fires or ViewModels survive it.

Static vs dynamic BroadcastReceiver registration and modern Android implications

Tests background limits, lifecycle coupling. Static manifest receivers survive app death but API 26 blocks most implicit broadcasts; dynamic receivers run with the context and must be unregistered. Red flag: static registration handles all implicit broadcasts.

When and why use a Foreground Service on API 26+?

Tests background execution limits. Good answer: use for noticeable long-running work; declare FOREGROUND_SERVICE, show a notification, and respect API 26 background start limits. Red flag: calling it invisible work or omitting the notification.

Describe the back stack for A to B to C with singleTask

Tests singleTask plus taskAffinity, not rote memorization. With default affinity, C sits atop B in the same task; if C already existed, the system clears B and delivers onNewIntent. Red flag: claiming singleTask always spawns a new task.

Activity rotation: what happens to EditText text?

Rotation destroys and recreates the Activity; EditText auto-saves text if it has an ID, else onSaveInstanceState or SavedStateHandle.

Describe the Android Activity lifecycle and callback order

Away calls onPause then onStop; back calls onRestart, onStart, onResume; onCreate only runs after destruction.

How do you manage API keys across Gradle build variants securely?

Gitignore a properties file, load it in build.gradle, map secrets to BuildConfig or manifest placeholders by flavor, and commit safe defaults.

Which Android Studio Profiler tool diagnoses high memory usage and leaks?

Heap dump, check retained size for leaked Activities, trace reference chains to root retainer.

What is ADB? Describe two common commands and what they accomplish.

This tests command-line debugging fluency. Define ADB as a client-server bridge, then give two commands such as adb install for APK deployment and adb logcat for streaming device logs. Red flag: calling it the Android Studio debugger or omitting the daemon.

Which Android Studio tool inspects view hierarchy and what does it show?

Tests practical knowledge of runtime UI debugging tools. A strong answer names Layout Inspector, cites live view hierarchy with bounds and attributes, and distinguishes it from the static Layout Editor. Red flag: citing Logcat or the preview pane instead.

Explain what a Gradle product flavor is and give a free vs pro example

Tests understanding of build-variant dimensions beyond build types. A strong answer defines flavorDimensions, sets free and pro applicationIdSuffix values, and explains variant generation. Red flag: conflating flavors with build types or manual APK renaming.

App crash: debug with Logcat and breakpoints in Android Studio

This tests systematic debugging and Android Studio fluency. A strong answer reproduces the crash, filters Logcat for the fatal exception, sets a breakpoint on the offending frame, and inspects variables.

What is the res directory and how do you use orientation qualifiers?

Res/ holds non-code assets; create layout-port/ and layout-land/ with identical XML filenames for automatic framework selection.

What is the difference between project-level and module-level build.gradle?

Project level sets plugin repos and shared versions; module level sets dependencies, build types, and flavors.

What is AndroidManifest.xml and what key elements does it declare?

This tests your grasp of the system-app contract. Good answers cover component registration, permissions, and build metadata like package name and target SDK. A red flag is omitting install-time system discovery.

How would you implement a type-safe Kotlin DSL for a UI Form?

Tests Kotlin DSL scoping with lambda receivers and extensions. Strong answers sketch a Form builder using initTag, explain T.() -> Unit implicit this for child elements, and add DslMarker to block scope leaks. Red flag: describing it as simple method chaining.

What is a reified type parameter in Kotlin?

Tests JVM type erasure and inline function mechanics. Strong answer: reified preserves generic types at runtime via inline expansion, enabling is T checks without Class<T> passing. Red flag: claiming reified works without inline or outside functions.

Describe coroutine cancellation mechanics and cooperative suspend functions

Tests cooperative cancellation mechanics. cancel() sets a Job to cancelling; suspend functions check this at suspension points and throw CancellationException, yet a tight non-suspending loop never checks and keeps running.