Interview questions in Mobile Dev, page 22
Apply a CIFilter to a live camera feed
Use AVCaptureSession with AVCaptureVideoDataOutput, receive CMSampleBuffers in captureOutput via the sample buffer delegate on a serial queue, filter with CIImage, drop late frames.
How do AnimationController and TickerProvider work together to drive animations?
Tests your grasp of Flutter's imperative animation engine. AnimationController stores value and direction; TickerProvider (via vsync) schedules frame callbacks; paired they emit 60–120 ticks per second.
What is Dependency Injection and Hilt's benefit over manual instantiation?
Tests your grasp of inversion of control and why frameworks matter. A good answer defines DI as supplying dependencies from outside, states Hilt automates object graph creation and scoping, and notes manual instantiation scatters construction logic.
FlatList and list virtualization
Use FlatList (or SectionList) which virtualizes, rendering only items near the viewport and recycling as you scroll, unlike ScrollView which mounts everything.
React to location authorization changed in Settings
Implement locationManagerDidChangeAuthorization, which fires on launch and whenever status changes, read authorizationStatus, and start updates when authorized.
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 do you inject UserRepository into a ViewModel with Hilt?
Tests Hilt constructor injection for classes you own. Annotate UserRepository's constructor with @Inject so Hilt auto-provides it to consumers like a @HiltViewModel. Red flag: using a @Provides module for a class you control.
Cost of console.log and production-safe debugging
Each console.log serializes data and, when devtools are attached, crosses the bridge synchronously, blocking the JS thread; strip logs in release and use Flipper, dev tools, or remote crash and analytics tools.
Recognize objects in ARKit with a Core ML model
Pull the frame's capturedImage, run Vision/Core ML off the main thread, raycast the 2D detection point into the scene, add an ARAnchor.
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.
Explain Hilt scoping: @Singleton vs @ActivityRetainedScoped
Tests Hilt component lifecycles. Answer: @Singleton lives for the app process; @ActivityRetainedScoped survives config changes via ActivityRetainedComponent but dies when the activity finishes.
useMemo and useCallback for stable references
UseMemo caches a computed value, useCallback caches a function identity across renders; both prevent recompute and unnecessary re-renders of memoized children.
Unit test versus UI test in Xcode
Unit tests (XCTest) exercise code logic in-process and fast; UI tests (XCUITest) drive the app through the accessibility layer, slower and end-to-end.
In a CustomPainter, what is the purpose of the shouldRepaint method?
This tests Flutter repaint optimization. Answer: shouldRepaint compares old and new delegates, returning true only when visual properties differ so the framework skips paint calls. A red flag is returning true unconditionally, forcing useless repaints.
How do you inject two different OkHttpClient instances with Hilt?
Tests Hilt qualifiers for same-type bindings. Answer: define a custom @Qualifier (or @Named), annotate two @Provides methods and the injection site. Red flag: manual client creation or subclassing OkHttpClient instead of qualifying the binding.
What is Hermes and its advantages over JSC?
Hermes is an open-source engine optimized for RN, with faster startup via precompiled bytecode and lower memory use.
Unit test a ViewModel with a mocked NetworkService
Inject the protocol, supply a mock returning canned data, assert published state transitions.
Functional difference between @Binds and @Provides in Hilt
Tests if you understand Hilt code generation tradeoffs. @Binds wires an existing injectable implementation to an interface with less overhead; @Provides constructs instances manually.
How would you draw a line graph using Canvas and Path?
Use moveTo for the first point, lineTo for the rest, then Canvas.drawPath with a stroke Paint.
Which two Flipper plugins diagnose an unresponsive UI?
Use the React DevTools profiler to find expensive renders and the Performance/Hermes plugin to spot a blocked JS thread or low FPS.
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