Interview questions in Mobile Dev, page 21
Request the user's location one time
Add a usage description to Info.plist, set a CLLocationManager delegate, request when-in-use authorization, call requestLocation, handle didUpdateLocations and didFailWithError.
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.
Play a remote video with AVFoundation
Wrap the URL in AVPlayerItem, feed it to AVPlayer, render with AVPlayerLayer added to the view's layer (or AVPlayerViewController for controls).
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.
Building a custom native module
Write native classes in Kotlin/Java and Swift/Objective-C, expose methods via the module macros, register the module, and import via NativeModules with promises or events.
Track location continuously in the background
Set desiredAccuracy, distanceFilter, activityType; enable the Location background mode and allowsBackgroundLocationUpdates; request Always authorization.
How do you safely add a non-nullable column in sqflite?
Tests onCreate for fresh installs vs onUpgrade for existing data. Outline: bump version; in onUpgrade use ALTER TABLE ADD COLUMN NOT NULL DEFAULT for existing rows; keep onCreate as latest schema. Red flag: only changing onCreate so old users crash.
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.
Handling push notifications across app states
Foreground onMessage, background and quit setBackgroundMessageHandler and getInitialNotification, plus data-only messages and native background tasks like Background Fetch or Notification Service…
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.
Implicit vs explicit animations: AnimatedContainer or AnimationController?
Knowledge of Flutter's implicit versus explicit animation paradigms. Implicit widgets auto-animate property changes on rebuild; explicit controllers manage playback manually. Red flag: saying explicit is always superior or that implicit animations cannot stop.
Parse polymorphic media JSON with Kotlin sealed classes and custom serializers
Sealed Media with Image and Video; use Moshi Factory or kotlinx.serialization keyed on the type field.
Streaming accelerometer data without bridge overload
The bottleneck is flooding the async bridge and re-rendering at sensor rate; fix by throttling, processing in worklets or native, and animating via shared values not setState.
Display thousands of map annotations efficiently
Enable clustering via clusteringIdentifier, reuse views with dequeueReusableAnnotationView, render clusters with MKClusterAnnotation in viewFor.
Describe CustomPaint and CustomPainter and implement a circle
This tests Flutter's render delegation. Separate CustomPaint, the canvas widget, from CustomPainter, the drawing logic; cover canvas.drawCircle and shouldRepaint returning false. Red flags: calling setState in paint or ignoring shouldRepaint.
Configure OkHttp Cache for Retrofit and force network requests
This tests HTTP caching semantics in mobile networking. A strong answer covers Cache setup with a 50 MiB directory, server Cache-Control driving expiration, and CacheControl.FORCE_NETWORK to bypass.
The JS thread and why it bottlenecks performance
A single thread runs your JS, React reconciliation, and event handling; blocking it delays updates and gestures, and it is separate from the UI thread.
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