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Top 50 Most Asked Android App Development Interview Questions

The questions that appear most often across company-wise sets — master these first.

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We count how often each question appears across the 20 company-wise Android App Development practice sets on this site and show the 50 most common. They are the safest questions to master first.

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01

You need to cache API responses so the home screen opens instantly. What approach do you take?

Room, DataStore and WorkManagerIn 10 company setsMedium
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Store the response in Room, or a file for a single blob, and have the screen observe the cached data immediately while a refresh runs in the background, known as stale-while-revalidate. Store a timestamp to decide when cache is too old. HTTP caching with OkHttp Cache can also help for GET requests with proper cache headers. Show cached content first, then update smoothly when fresh data arrives.
02

How do you share data between two screens in a checkout flow?

App Architecture, MVVM and HiltIn 9 company setsMedium
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Options in order of preference: pass small IDs as navigation arguments and load the rest from a repository; store flow data in a repository scoped to the session; or use a ViewModel scoped to a nested navigation graph so all checkout screens share it and it is cleared when the flow ends. Avoid activity-scoped ViewModels holding everything, and avoid passing large objects through arguments.
03

How do you handle one-time navigation after a successful login in MVVM?

App Architecture, MVVM and HiltIn 9 company setsMedium
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Recommended practice is to reflect the result in state, such as isLoggedIn = true in UiState, and have the UI react with LaunchedEffect(state.isLoggedIn) to navigate, then the ViewModel marks it consumed if needed. An alternative is a Channel exposed as Flow and collected with lifecycle awareness. Avoid calling navigation directly from the ViewModel, because it should not reference NavController or views.
04

A crash report shows a NullPointerException in Kotlin code. How can that happen if Kotlin is null safe?

Kotlin FundamentalsIn 8 company setsMedium
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Common causes are the !! operator, platform types from Java code without nullability annotations, accessing a lateinit property before assignment, calling a function from a constructor before properties are initialised, and reflection-based libraries like Gson setting non-null fields to null. Fix it by removing !!, adding annotations or explicit nullable types at the Java boundary, and using a Kotlin-aware serializer such as kotlinx.serialization or Moshi with Kotlin codegen.
05

Write code to fetch two API results in parallel inside a ViewModel.

Coroutines and FlowIn 8 company setsMedium
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fun loadDashboard() { viewModelScope.launch { _state.value = UiState.Loading try { val (profile, orders) = coroutineScope { val p = async { repo.getProfile() } val o = async { repo.getOrders() } p.await() to o.await() } _state.value = UiState.Success(profile, orders) } catch (e: IOException) { _state.value = UiState.Error("Network error") } } }
06

How should a Fragment or Activity collect a Flow safely?

Coroutines and FlowIn 8 company setsMedium
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Use lifecycleScope.launch with repeatOnLifecycle(Lifecycle.State.STARTED) so collection starts when the UI is visible and stops in the background, avoiding wasted work and crashes from updating views that are not ready. In a Fragment, use viewLifecycleOwner.lifecycleScope because the fragment view can be destroyed while the fragment lives. In Compose, use collectAsStateWithLifecycle(), which does the same lifecycle-aware collection.
07

Write a manifest entry for a deep link that opens a product screen.

Android Components and LifecycleIn 8 company setsMedium
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<activity android:name=".MainActivity" android:exported="true"> <intent-filter android:autoVerify="true"> <action android:name="android.intent.action.VIEW" /> <category android:name="android.intent.category.DEFAULT" /> <category android:name="android.intent.category.BROWSABLE" /> <data android:scheme="https" android:host="shop.example.com" android:pathPrefix="/product" /> </intent-filter> </activity> <!-- autoVerify plus assetlinks.json on the domain makes it an App Link -->
08

A ViewModel has grown to 1500 lines handling many responsibilities. How would you refactor it?

App Architecture, MVVM and HiltIn 8 company setsMedium
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First add tests around current behaviour so refactoring is safe. Then extract business logic into use cases or domain classes, move data mapping into repositories or mappers, and split UI state into smaller, focused data classes. If the screen truly has separate areas, consider separate state holders or child ViewModels per section. Refactor in small pull requests so reviewers can follow and regressions are easy to locate.
09

How do you write tests for a Room DAO?

Room, DataStore and WorkManagerIn 8 company setsMedium
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Create an in-memory database with Room.inMemoryDatabaseBuilder in an instrumented test or with Robolectric, get the DAO, insert test data and assert query results. For Flow queries, collect the first value with first() or use Turbine. Close the database in @After. Test edge cases like conflict strategies and ordering. In-memory databases are fast and isolated, so each test starts clean.
10

How do you migrate from SharedPreferences to DataStore without losing user data?

Room, DataStore and WorkManagerIn 8 company setsMedium
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Use SharedPreferencesMigration when creating the DataStore: preferencesDataStore(name = "settings", produceMigrations = { ctx -> listOf(SharedPreferencesMigration(ctx, "old_prefs")) }). On first access, DataStore copies the values and deletes the old file. Update all reads and writes to go through the new repository at once, because mixing both stores leads to inconsistent values. Test the migration with existing preference files.
11

Write a Room database class with a migration that adds a column.

Room, DataStore and WorkManagerIn 8 company setsMedium
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@Database(entities = [NoteEntity::class], version = 2, exportSchema = true) abstract class AppDatabase : RoomDatabase() { abstract fun noteDao(): NoteDao } val MIGRATION_1_2 = object : Migration(1, 2) { override fun migrate(db: SupportSQLiteDatabase) { db.execSQL("ALTER TABLE notes ADD COLUMN pinned INTEGER NOT NULL DEFAULT 0") } } val db = Room.databaseBuilder(context, AppDatabase::class.java, "app.db") .addMigrations(MIGRATION_1_2) .build()
12

Images in a feed load slowly and the app runs out of memory. What do you change?

Networking and APIsIn 8 company setsMedium
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Use an image library like Coil, which handles memory and disk caching, request downsampling to the view size, and cancellation when items scroll away. Ask the backend or CDN for resized, compressed images such as WebP instead of full-size originals. Use placeholders and crossfade, avoid holding Bitmaps in ViewModels, and set memory cache limits. Profile with Memory Profiler to confirm the large allocations are gone.
13

QA says a bug happens only on one manufacturer's phones. How do you debug it?

Testing, Performance and Play StoreIn 8 company setsMedium
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Get exact device model, OS and skin versions, and steps. Use a remote device lab or Firebase Test Lab to reproduce if you lack the device. Collect logcat and bug reports, and compare behaviour around known differences like battery optimisation, autostart restrictions, custom permission dialogs or WebView versions. Add targeted logging or a non-fatal Crashlytics event, then apply a fix guarded by checks only if necessary.
14

Your banking app must pass a security audit. What would you check on the Android side?

Testing, Performance and Play StoreIn 8 company setsHard
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Check secure storage with Keystore and no secrets in code, TLS only with pinning where justified, no sensitive data in logs, FLAG_SECURE on sensitive screens, root and tamper checks using Play Integrity, exported components reviewed, WebView with JavaScript bridges restricted, R8 obfuscation, session timeout, and biometric authentication with BiometricPrompt and CryptoObject. Use the OWASP MASVS as the checklist and fix findings by severity.
15

Write a Flow that combines user settings and product list into one UI state.

Coroutines and FlowIn 7 company setsMedium
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val uiState: StateFlow<HomeState> = combine( settingsRepo.settings, productRepo.products ) { settings, products -> HomeState( currency = settings.currency, items = products.sortedBy { it.price } ) }.stateIn( scope = viewModelScope, started = SharingStarted.WhileSubscribed(5000), initialValue = HomeState() )
16

How do you build a single-activity app with the Navigation component?

Android Components and LifecycleIn 7 company setsMedium
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Keep one Activity hosting a NavHost, and represent each screen as a Compose destination or Fragment. Define routes in a navigation graph, preferably with type-safe routes using Kotlin serialization in Navigation 2.8 and later. Use nested graphs for flows like login or checkout, pop the back stack with popUpTo when finishing a flow, and handle deep links on destinations. This simplifies shared transitions and state handling.
17

A WorkManager job is not running on some phones from certain manufacturers. How do you investigate?

Room, DataStore and WorkManagerIn 7 company setsHard
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Some manufacturers apply aggressive battery optimisations that delay or kill background work. Check the job state with WorkManager's getWorkInfosForUniqueWorkFlow and the background task inspector in Android Studio. Verify constraints are not too strict. Guide users to allow unrestricted battery for the app only where the feature truly needs it, use expedited work for urgent tasks, and use FCM to trigger sync when timely delivery matters.
18

Your app shows duplicate orders when users tap Pay twice on a slow network. How do you fix it?

Networking and APIsIn 7 company setsHard
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Disable the button and show progress once tapped, but do not rely only on the UI. Generate an idempotency key on the client for each checkout attempt and send it with the request so the server returns the same result for retries. Ensure the payment call is not retried automatically by OkHttp for non-idempotent POSTs, and let the user check order status if the response is lost.
19

Write a unit test for a ViewModel using a fake repository and runTest.

Testing, Performance and Play StoreIn 7 company setsMedium
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class ProductViewModelTest { @get:Rule val mainRule = MainDispatcherRule() @Test fun loadsProductsIntoState() = runTest { val fake = FakeProductRepository(listOf(Product("1", "Pen", 10.0))) val vm = ProductViewModel(fake) advanceUntilIdle() val state = vm.state.value assertFalse(state.loading) assertEquals(1, state.items.size) assertNull(state.error) } }
20

How do you find and fix memory leaks in an Android app?

Testing, Performance and Play StoreIn 7 company setsMedium
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Add LeakCanary to debug builds; it detects retained Activities, Fragments and ViewModels and shows the reference chain. Common leaks are static or singleton references to Context or Views, listeners not unregistered, inner classes holding Activity references, and Fragment view bindings not cleared in onDestroyView. Fix by using application context, lifecycle-aware components and weak references only where needed. Confirm with Memory Profiler heap dumps.
21

The crash-free rate dropped after a release only on Android 15 devices. How do you respond?

Testing, Performance and Play StoreIn 7 company setsMedium
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Halt the staged rollout immediately. Filter Crashlytics or Play vitals by OS version to find the top crash, then check Android 15 behaviour changes such as edge-to-edge enforcement, foreground service rules or new restrictions affecting your target SDK. Reproduce on an Android 15 emulator, fix, add a test, and resume rollout with the hotfix. Afterward, add Android 15 devices to the regular test matrix.
22

Your team is migrating a Java Android app to Kotlin. How would you plan it?

Kotlin FundamentalsIn 6 company setsMedium
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Kotlin and Java interoperate, so migrate gradually rather than all at once. Start with new features in Kotlin, then convert leaf classes like models and utilities, writing tests before converting. Add nullability annotations to Java code so Kotlin sees correct types. Review auto-converted code because it often overuses !!. Track progress per module and agree on style rules with ktlint or detekt so the codebase stays consistent.
23

The app shows an ANR when the user taps Save. The save function is suspend. What could be wrong?

Coroutines and FlowIn 6 company setsMedium
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A suspend function does not automatically run off the main thread. If it calls blocking code, like a synchronous file write, a SharedPreferences commit, a blocking SDK or heavy JSON parsing, it still blocks the main thread. Check with a profiler or StrictMode. Fix by wrapping the blocking part in withContext(Dispatchers.IO) or Default, or by using main-safe APIs such as Room suspend DAOs or DataStore.
24

A screen shows a snackbar again every time the device rotates. How do you fix it?

Coroutines and FlowIn 6 company setsMedium
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The event is probably stored as state in a StateFlow or LiveData, so it is re-delivered when the new Activity collects again. Options: model it as part of UI state and have the UI call a function like onMessageShown() to clear it after display, which is the approach the official guidance recommends; or send it through a Channel exposed with receiveAsFlow so each event is consumed once. Collect with lifecycle awareness to avoid losing events.
25

What is a BroadcastReceiver and what limits apply since Android 8?

Android Components and LifecycleIn 6 company setsMedium
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A BroadcastReceiver responds to broadcast intents. Since Android 8, most implicit broadcasts cannot be received by receivers declared in the manifest; you register them at runtime with registerReceiver while the app is running. A few exemptions exist, like BOOT_COMPLETED and locale change. Since Android 14, runtime receivers must specify RECEIVER_EXPORTED or RECEIVER_NOT_EXPORTED. onReceive runs on the main thread, so keep it short or use goAsync.
26

Your team wants to migrate a large XML app to Compose. How would you plan it?

Jetpack ComposeIn 6 company setsMedium
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Start by setting up a shared Compose theme matching the existing design system, then build new screens in Compose. Migrate leaf components and simple screens next, using ComposeView inside fragments, and leave complex custom views wrapped in AndroidView for later. Measure performance with Macrobenchmark and add Baseline Profiles. Add Compose UI and screenshot tests, train the team, and set a rule that new UI is Compose-only.
27

How do you build an adaptive layout for phones, foldables and tablets in Compose?

Jetpack ComposeIn 6 company setsHard
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Use WindowSizeClass from the Material 3 adaptive library to choose layouts by width class, not device type. On compact width show a bottom navigation bar; on medium use a navigation rail; on expanded use a list-detail layout with ListDetailPaneScaffold or NavigationSuiteScaffold. Avoid locking orientation, since Android 16 ignores orientation restrictions on large screens. Test with resizable emulators and foldable postures.
28

Write a Hilt module that provides Retrofit and a repository binding.

App Architecture, MVVM and HiltIn 6 company setsMedium
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@Module @InstallIn(SingletonComponent::class) object NetworkModule { @Provides @Singleton fun provideRetrofit(): Retrofit = Retrofit.Builder() .baseUrl("https://api.example.com/") .addConverterFactory(Json.asConverterFactory("application/json".toMediaType())) .build() @Provides @Singleton fun provideApi(retrofit: Retrofit): ShopApi = retrofit.create(ShopApi::class.java) } @Module @InstallIn(SingletonComponent::class) abstract class RepoModule { @Binds abstract fun bindRepo(impl: ProductRepositoryImpl): ProductRepository }
29

Users who reinstall the app lose all their settings. How can you restore them?

Room, DataStore and WorkManagerIn 6 company setsMedium
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Android Auto Backup automatically backs up app data to the user's cloud backup account for apps targeting API 23 and above, unless disabled. Configure dataExtractionRules for Android 12 and above to include settings files and exclude tokens or caches. For important data like notes, sync to your own server tied to the user's account, since backup is not guaranteed. Test with adb shell bmgr commands.
30

Users on slow 2G and 3G networks in small towns report the app keeps failing. How do you improve it?

Networking and APIsIn 6 company setsMedium
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Set reasonable connect and read timeouts, retry idempotent requests with exponential backoff, and cache responses so screens show something offline. Reduce payload size with gzip, pagination and fields filtering, and load images in smaller sizes with placeholders. Show clear offline and retry states instead of generic errors. Test with the emulator network throttling and real devices on poor connections, and track failure rates by network type.
31

A payment SDK integration fails only in release builds. What would you check?

Networking and APIsIn 6 company setsMedium
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First check R8 or ProGuard: release builds shrink and obfuscate code, and the SDK may need keep rules for classes used by reflection or JSON parsing. Check the SDK documentation for required rules and add them to proguard-rules.pro. Also verify the release signing key SHA is registered with the provider, the correct production keys and base URLs are used, and network security config allows the domains.
32

Tell me about a time you worked closely with a backend team to solve a problem.

Networking and APIsIn 6 company setsMedium
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Situation: our feed took four seconds to load because the app made six API calls. Task: reduce load time. Action: I measured each call with network profiling, shared a timeline with the backend team, and we agreed on one aggregated endpoint with only the fields the screen used, plus pagination. I updated the client and added caching. Result: load time dropped to under one second and both teams reused the approach.
33

The app's cold start takes 4 seconds. How do you improve it?

Testing, Performance and Play StoreIn 6 company setsHard
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Measure first with Macrobenchmark StartupTimingMetric on a release build. Then reduce work in Application.onCreate by deferring SDK initialisation, using App Startup or lazy injection, and moving disk I/O off the main thread. Simplify the first screen, avoid blocking on network before showing UI, use the SplashScreen API properly, and add a Baseline Profile, which often improves startup by about 20 to 30 percent.
34

The Play Store rejected your update for a policy violation about permissions. What do you do?

Testing, Performance and Play StoreIn 6 company setsMedium
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Read the rejection email and policy centre message carefully to see which permission or declaration failed, often SMS, call log, background location, all-files access or exact alarms. Remove the permission if a less sensitive alternative exists, such as the SMS Retriever API or photo picker. Otherwise update the permission declaration form with a clear use case and video. Check the merged manifest for permissions added by libraries.
35

The APK size grew to 120 MB and installs from small towns are dropping. How do you reduce it?

Testing, Performance and Play StoreIn 6 company setsMedium
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Analyse the build with APK Analyzer. Publish as an App Bundle so users get only their density, language and ABI. Enable R8 and resource shrinking, convert images to WebP or vectors, remove unused libraries and duplicate dependencies, and move large optional features or assets to Play Feature Delivery or Play Asset Delivery. Avoid bundling all native libraries for every ABI. Track size in CI.
36

Write a delegated property that logs whenever a value changes.

Kotlin FundamentalsIn 5 company setsMedium
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import kotlin.properties.Delegates class Settings { var theme: String by Delegates.observable("light") { prop, old, new -> println("${prop.name} changed from $old to $new") } } // Use Delegates.vetoable if you need to reject a change // by returning false from the lambda.
37

What does the suspend keyword mean?

Coroutines and FlowIn 5 company setsEasy
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suspend marks a function that can pause and resume later without blocking the thread. It can only be called from another suspend function or a coroutine. The compiler transforms it using continuation-passing style into a state machine. suspend alone does not move work to a background thread; the function must use withContext(Dispatchers.IO) or a main-safe library like Retrofit or Room to avoid blocking the main thread.
38

Explain StateFlow versus SharedFlow.

Coroutines and FlowIn 5 company setsMedium
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StateFlow is a hot flow that always has a current value, replays only the latest value to new collectors and skips emissions equal to the current value. It is ideal for UI state. SharedFlow is a configurable hot flow with no required initial value, optional replay and buffer, and it emits every value including duplicates. It suits one-off events like navigation or snackbars, though many teams prefer a Channel or state-based events for those.
39

Write a suspend function that wraps a callback-based API.

Coroutines and FlowIn 5 company setsHard
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suspend fun FusedLocationProviderClient.awaitLastLocation(): Location? = suspendCancellableCoroutine { cont -> lastLocation .addOnSuccessListener { cont.resume(it) } .addOnFailureListener { cont.resumeWithException(it) } cont.invokeOnCancellation { /* cancel request if supported */ } } // For streams of callbacks, use callbackFlow { } with awaitClose { }.
40

You need to sync 500 images to a server without overloading the network. How would you design it with coroutines?

Coroutines and FlowIn 5 company setsHard
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Limit concurrency. Use a Semaphore with withPermit around each upload, or flatMapMerge(concurrency = 4) over a flow of files, or Dispatchers.IO.limitedParallelism(4). Use supervisorScope so one failed upload does not cancel the rest, collect failures for retry with backoff, and report progress through a StateFlow. If the sync must survive app exit, run it inside a CoroutineWorker with WorkManager constraints such as network connected.
41

Users report the app loses form data when they switch to another app and come back after a while. Why?

Android Components and LifecycleIn 5 company setsMedium
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The system killed the process to reclaim memory while the app was in the background. When the user returns, Android recreates the Activity but ViewModel data is gone because the process died. Fix it by storing small UI state in SavedStateHandle or rememberSaveable, which survive process death, and persisting drafts to Room or DataStore. Test with Don't keep activities or adb shell am kill.
42

Tell me about a time you handled a production crash under pressure.

Android Components and LifecycleIn 5 company setsMedium
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Situation: after a release, crash-free users dropped from 99.6 to 97 percent. Task: stop the impact fast. Action: I checked Crashlytics, found a crash on Android 14 caused by a missing foreground service type, paused the staged rollout in Play Console, shipped a hotfix with a test on an emulator for that API level, and wrote a short postmortem. Result: crash rate recovered within a day and we added API-level checks to our release checklist.
43

Explain LaunchedEffect, DisposableEffect and SideEffect.

Jetpack ComposeIn 5 company setsMedium
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LaunchedEffect(key) launches a coroutine when it enters composition and restarts when the key changes, used for one-time loads or showing a snackbar. DisposableEffect(key) runs setup and requires an onDispose block for cleanup, used for registering listeners or lifecycle observers. SideEffect runs after every successful recomposition to publish Compose state to non-Compose code, such as analytics. Choose keys carefully so effects do not restart unexpectedly.
44

Write a Compose UI test that checks an error appears when login is clicked with an empty email.

Jetpack ComposeIn 5 company setsMedium
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@get:Rule val rule = createComposeRule() @Test fun showsErrorForEmptyEmail() { rule.setContent { var state by remember { mutableStateOf(LoginState()) } LoginScreen( state = state, onLogin = { state = state.copy(error = "Email required") } ) } rule.onNodeWithText("Login").performClick() rule.onNodeWithText("Email required").assertIsDisplayed() }
45

Write a HiltViewModel that exposes a single UiState using StateFlow.

App Architecture, MVVM and HiltIn 5 company setsMedium
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data class ProductUiState( val loading: Boolean = true, val items: List<Product> = emptyList(), val error: String? = null ) @HiltViewModel class ProductViewModel @Inject constructor( private val repo: ProductRepository ) : ViewModel() { private val _state = MutableStateFlow(ProductUiState()) val state: StateFlow<ProductUiState> = _state.asStateFlow() init { refresh() } fun refresh() = viewModelScope.launch { _state.update { it.copy(loading = true, error = null) } runCatching { repo.fetchProducts() } .onSuccess { list -> _state.update { it.copy(loading = false, items = list) } } .onFailure { _state.update { it.copy(loading = false, error = "Try again") } } } }
46

What is the difference between @Provides and @Binds in Hilt?

App Architecture, MVVM and HiltIn 5 company setsMedium
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@Provides is used in a module function that constructs and returns an object, needed for third-party classes like Retrofit or Room that you cannot annotate with @Inject. @Binds is used on an abstract function in an abstract module to tell Hilt which implementation to use for an interface, when the implementation already has an @Inject constructor. @Binds generates less code and is slightly more efficient.
47

Two screens show different values for the same cart count. How do you fix the architecture?

App Architecture, MVVM and HiltIn 5 company setsMedium
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Each screen probably fetches and caches its own copy. Create a single CartRepository, scoped as a singleton, that owns cart data in Room or an in-memory StateFlow, and have both ViewModels observe its Flow instead of keeping private copies. Mutations go through the repository so every observer updates automatically. This enforces the single source of truth and removes the need for manual refresh calls between screens.
48

How do you store sensitive data such as tokens securely on Android?

Room, DataStore and WorkManagerIn 5 company setsHard
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Never store secrets in plain SharedPreferences or hardcode them in code. Use the Android Keystore to generate a key that never leaves secure hardware, and encrypt the data before storing it in DataStore or a file. The security-crypto EncryptedSharedPreferences library is deprecated, so many teams use Tink with Keystore. Keep tokens short-lived with refresh tokens, and clear them on logout. Exclude them from backups.
49

After an app update, users report that the app crashes on launch. Logs show a Room migration error. What do you do?

Room, DataStore and WorkManagerIn 5 company setsMedium
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Immediately halt the staged rollout in Play Console. Reproduce by installing the previous version, adding data, and upgrading. The schema version was probably increased without a matching migration, or a migration SQL does not match the new entity. Write the correct Migration, test it with MigrationTestHelper from every supported old version, and release a hotfix. Avoid destructive fallback because it deletes user data.
50

What conflict strategies does Room offer for inserts?

Room, DataStore and WorkManagerIn 5 company setsMedium
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@Insert(onConflict = ...) supports REPLACE, which deletes the old row and inserts the new one; IGNORE, which skips the insert; ABORT, the default, which rolls back the transaction; and others. REPLACE can trigger cascading deletes on foreign keys because it deletes first. @Upsert, added in Room 2.5, inserts or updates without deleting, making it safer for syncing server data into local tables.

Frequently asked questions

How is this list made?

We count how often each question appears across the 20 company-wise Android App Development practice sets on this site and show the 50 most common. They are the safest questions to master first.

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