📱 Mobile Dev

Testing async code and completion handlers in XCTest

Create an expectation, fulfill it inside the completion handler, call wait with a timeout, or use async test methods.

advanced2 min read

Implement staggered animations using a single AnimationController and Interval

This tests multiplexing one ticker into sequential animations. Use one AnimationController, map each Tween to an Interval on distinct 0-to-1 sub-ranges, and rebuild with AnimatedBuilder. Red flag: multiple controllers or manual forward chaining.

intermediate2 min read

How would you access a Hilt dependency in a non-injectable ContentProvider?

Tests Hilt's escape hatch for framework classes. Strong answer: define an EntryPoint in SingletonComponent, expose the dependency, and retrieve it with EntryPointAccessors.fromApplication. Red flag: field injection or manual static singletons.

What is bridge traffic and what causes dropped frames?

The bridge passes batched, serialized JSON messages between JS and native asynchronously; high-frequency events flood it.

Locating XCUITest elements without accessibility identifiers

Query by type, label, predicate, or index; chain queries to narrow scope.

Diagnosing and fixing CustomPainter jank

Avoid work in paint, gate repaints with shouldRepaint, isolate with RepaintBoundary, cache static layers.

advanced2 min read

Replace a production NetworkService with a fake in Hilt instrumented tests

Tests whether you know Hilt test overrides beyond basic DI. A strong answer covers @BindValue for field-level fakes and @TestInstallIn or @UninstallModules for module swaps.

How do Fabric, TurboModules, and JSI fix bridge limits?

JSI lets JS hold C++ host objects and call native synchronously without JSON serialization; Fabric renders concurrently and TurboModules lazy-load.

Code coverage and its pitfalls

It measures executed lines, surfaces untested paths, and guides where to add tests.

Building a custom implicitly animated widget

Extend ImplicitlyAnimatedWidget, use AnimatedWidgetBaseState, define tweens in forEachTween, read values in build.

advanced2 min read

Describe Hilt's component hierarchy and scope injection rules

Tests whether you understand Hilt's generated component tree and scoping rules. A strong answer lists the hierarchy, explains parent-outlives-child semantics, and states that ActivityScoped-into-Singleton injection fails at compile time.

How do you move a 500ms blocking task off the JS thread?

Offload to a native module or C++ TurboModule, a worklet/worker thread, or chunk the work and yield; never block JS.

Diagnosing and stabilizing flaky XCUITests

Identify timing races, animations, network variance, and shared state; fix with expectations, controlled launch state, and isolation.

What native iOS and Android config does the Flutter camera plugin need?

Tests native platform knowledge beyond Dart. iOS requires NSCameraUsageDescription and NSMicrophoneUsageDescription in Info.plist. Android needs minSdk 24 and choosing between CameraX or Camera2 implementations.

How do you make a network request in an Activity using coroutines?

This tests main thread safety and coroutine dispatchers. A strong answer cites NetworkOnMainThreadException, uses lifecycleScope, and switches to Dispatchers.IO. Red flag: suggesting Dispatchers.Main for the network call or omitting the exception entirely.

How do you debug a memory leak with Hermes heap snapshots?

Take a baseline snapshot, exercise the suspect flow repeatedly, snapshot again, and compare retained sizes and object counts that grow monotonically.

Driving app state via launch arguments in XCUITest

Pass launchArguments and launchEnvironment, read them at startup to seed auth and flags, bypassing slow UI steps.

Explain the purpose of MethodChannel and how it enables Dart-to-native calls

MethodChannel lets Dart encode a method call; the platform host decodes it on the main thread, runs native code, and returns an async result.