Intermediate interview questions in Mobile Dev, page 9
Difference between frame, bounds, and center
Frame and center are in the superview's space; bounds is the view's own space, usually origin zero. A non-identity transform makes frame undefined to read.
How would you manage network request state in a Flutter widget?
This tests whether you separate ephemeral widget state from business logic. A good answer defines a state class, uses setState in initState, then shows how a library moves logic out for testing and reuse. Red flag: fetch inside build or using boolean flags.
Model a Room one-to-many Playlist-to-Song relationship
Tests Room relational modeling. Strong answer: Song foreign key, @Embedded Playlist with @Relation to List<Song>, DAO wrapped in @Transaction. Red flag: embedding songs in Playlist or skipping @Transaction, which causes N+1 queries.
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.
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.
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.
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.
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.
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.
Explain Retrofit Interceptors and write a static API key interceptor
Tests OkHttp interception and application versus network scope. Strong answers build a new request adding X-Api-Key via newBuilder and chain.proceed; contrast addInterceptor once versus addNetworkInterceptor per hop.
Key difference between shared_preferences and flutter_secure_storage for tokens
Tests at-rest encryption: shared_preferences stores plain text XML/plist, while secure storage uses iOS Keychain and Keystore with RSA OAEP plus AES-GCM. Answers cite backup risks and hardware keys. Red flag: calling prefs safe or relying on obfuscation.
Managing camera lifecycle in Vision Camera
Bind the isActive prop to screen focus via useIsFocused and to app state, so the camera stops when blurred or backgrounded.
What is an sqflite transaction? Provide a practical example.
Tests atomicity in SQLite and isolate safety. A strong answer defines all-or-nothing execution, gives a fund-transfer example updating both, and warns sqflite transactions are not cross-isolate safe. Red flag: omitting rollback or multi-isolate writes.
How do you differentiate network and server errors in suspend functions?
Catch IOException for connectivity and HttpException for HTTP errors; wrap in a sealed Result.
Track location continuously in the background
Set desiredAccuracy, distanceFilter, activityType; enable the Location background mode and allowsBackgroundLocationUpdates; request Always authorization.
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.
Run a Core ML image model with Vision
Add the .mlmodel so Xcode generates a class, wrap it in a VNCoreMLModel, run a VNCoreMLRequest via a VNImageRequestHandler, read results off the main queue.
Display thousands of map annotations efficiently
Enable clustering via clusteringIdentifier, reuse views with dequeueReusableAnnotationView, render clusters with MKClusterAnnotation in viewFor.
Compare AnimatedBuilder and Transition widgets for explicit animations
Tests whether you know how explicit animations rebuild the widget tree and where to isolate animation effects. AnimatedBuilder rebuilds only its builder subtree, while Transition widgets rebuild their child when the animation ticks.
How does Tween work and how do you use ColorTween with Curves?
This tests value interpolation versus time remapping. A strong answer: Tween maps 0-1 to typed values; ColorTween lerps 2 colors; Curves.easeInOut warps input time before interpolation. Red flag: claiming the curve alters the color output instead of timing.
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