Interview questions in Mobile Dev, page 20
Build a custom circular progress bar in UIKit
Draw an arc with UIBezierPath, assign it to a CAShapeLayer path, set lineWidth and no fill, animate strokeEnd 0 to 1.
Explain Dio interceptors and automatic token refresh
Define interceptors as hooks; queue concurrent 401s during refresh; retry with Bearer header via token manager.
Preferences vs Proto DataStore: when is Proto significantly better?
This tests type safety and schema trade-offs. A strong answer contrasts Preferences key-value pairs with Proto typed protobuf schemas, then names nested settings or migration needs as the Proto win. A red flag is recommending Proto for a single boolean.
Persisting key-value preferences across launches
AsyncStorage for simple non-sensitive key-value, MMKV for speed, SecureStore or Keychain for secrets.
Allow simultaneous pan and pinch gestures
Attach pan and pinch recognizers, set yourself as delegate, return true from shouldRecognizeSimultaneouslyWith, apply translation to center and scale to transform.
Implement an API caching layer with offline support and storage trade-offs
Use in-memory for hot data and disk for offline, pick Hive or SQLite by shape, and use TTL with a sync queue.
Room DAO: Flow<List<User>> vs suspend fun getUsers(): List<User>
This tests reactivity versus one-shot queries in Room and coroutines. Flow emits on every table change on Room's dispatcher, while suspend returns a single snapshot requiring manual refresh.
Requesting runtime permissions on iOS and Android
Declare permissions in Info.plist and AndroidManifest, then check status and request at runtime just before use, handling granted, denied, and blocked.
Diagnose dropped frames during animation
Use Core Animation and color-debug options to spot off-screen passes, blending, and overdraw; cache, flatten, and set shadowPath.
Why are stale search requests problematic and how do you cancel them?
This tests race conditions and resource waste in async UI. Strong answers note stale requests waste bandwidth and overwrite newer results; cancel the previous call with a CancelToken before issuing the next.
How would you implement a robust offline-first repository?
Tests single-source-of-truth discipline and network-local sync. Outline a Room repository with Flow, background refresh, disk persistence, immediate local emission, and conflict resolution with retry.
Getting a one-time GPS location
Ensure permission, then call a getCurrentPosition wrapped in a promise (or Expo Location.getCurrentPositionAsync) with await inside try/catch, reading coords.latitude and longitude.
Build an interruptible custom VC transition
A delegate vends an animator (UIViewControllerAnimatedTransitioning) for the visuals and an interactive controller (UIViewControllerInteractiveTransitioning) driven by a pan to scrub progress and…
How would you use Retrofit to GET /posts/{id} and key components?
This checks your understanding of Retrofit's three-layer setup. You need a data class for JSON parsing, an interface with @GET and @Path, and a Retrofit.Builder with baseUrl and a converter.
When to use SQLite over key-value storage?
Tests structured-vs-flat storage judgment. Good answers cite relational data, complex queries, or multi-table schemas, then list adding the dependency, getting a path, opening with onCreate, and keeping a singleton.
Push notification data flow with APNs and FCM
Device registers and gets a token, server sends to FCM, FCM routes to APNs for iOS and directly for Android, the OS delivers to the app.
Animate a SwiftUI Shape morphing point count
Expose a continuous sides value as animatableData so SwiftUI interpolates it, then compute the path from that fractional value each frame.
Why is Flutter local storage async and how do you use shared_preferences?
Tests why disk I/O must avoid blocking Dart's UI thread. A strong answer shows async/await with getInstance and setters, notes legacy getters are sync-after-cache, and warns writes may not persist instantly.
How do you configure Moshi or Kotlinx.serialization for JSON key mismatches?
This tests library-specific field-mapping annotations. For Kotlinx.serialization use @SerialName with the JSON key; for Moshi use @Json with the name parameter. A red flag is confusing the two or using manual mapping instead of the built-in decorator.
Background GPS tracking challenges and approaches
Request always-allow permission, declare background modes, use a native background task or geofencing API rather than JS timers, manage battery and OS throttling.
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