📱 Mobile Dev

When would you implement a CustomPainter and how does shouldRepaint work?

Use CustomPainter for charts; check fields in shouldRepaint to skip frames; pass Listenable to bypass build layout.

What is a Dart Isolate and how does it differ from threads?

Tests Dart's shared-nothing concurrency model. Define an isolate as an independent heap plus event loop, contrast it with shared-memory threads, and explain UI isolate communication via async message ports.

Explain 'constraints go down, sizes go up, parent sets position.'

Tests Flutter layout protocol and unbounded width errors. Strong answers trace how a child gets infinite width from a scrolling parent and fix it with a bounded wrapper. Red flag: blaming the child without tracing parent constraints.

Which DevTools view diagnoses janky Flutter animations?

Open Performance view; compare UI and Raster bars; flag bars over 16ms; blame UI bloat on builds and Raster jank on shaders or saveLayer.

Walk me through Flutter's rendering pipeline and its phases.

Tests your understanding of the three-tree separation and how changes become pixels. Outline: setState marks objects dirty; Build updates elements, Layout computes sizes bottom-up via constraints, and Paint records commands top-down into layers.

Flutter's Widget, Element, and RenderObject trees: roles and relationships

Tests your mental model of Flutter's rendering layers. Strong answer: Widget is immutable configuration; Element is the mutable lifecycle manager owning the RenderObject; RenderObject is the concrete layout and paint entity.

Why use const for Flutter widgets and how does it improve performance?

Tests widget canonicalization and rebuild short-circuiting. Strong answer: const enables instance reuse and skips subtree rebuilds on parent updates, reducing allocations.

Debug iOS code signing failure in CI that works locally

This tests Xcode code signing and CI keychain isolation. A strong answer checks exportOptions.plist, keychain profile presence, runner OS and Xcode versions, and entitlements mismatches. Red flag: manual local fixes or ignoring keychain access gaps.

How do you handle platform-specific configurations per flavor on Android and iOS?

Tests if you know flavors delegate icons and titles to native tooling. On Android, use productFlavors in build.gradle with source sets or placeholders; on iOS, use Xcode build configurations with Info.plist values or asset catalogs.

intermediate3 min read

Walk me through a Flutter CI/CD pipeline for Play Store and TestFlight

Tests your ability to orchestrate multi-platform Flutter builds, manage signing secrets, and automate deployments to Google Play Internal Testing and Apple TestFlight.

What does flutter build appbundle --release do to minimize size?

Dart AOT compiles and tree-shakes dead code; R8 shrinks Android Java/Kotlin; app bundles split by ABI.

How would you manage different backend environments in a Flutter project?

Tests Flutter build flavors and compile-time config injection. A strong answer uses dart-define or flavor-specific entry points plus an EnvironmentConfig abstraction. A red flag is manually swapping hard-coded base URLs before each build.

Flutter command for an Android release build and APK vs AAB difference.

Flutter CLI release commands and Android distribution formats. Name flutter build apk and flutter build appbundle; note AAB lets Google Play generate optimized APKs per device while APK is a single direct-install file.

How do you diagnose and fix flaky Flutter widget tests?

Audit unawaited futures, swap pumpAndSettle for explicit pumps or mock timers, and reproduce with logs.

Unit test a BLoC handling an AddItem event and emitting state

Use blocTest with build, act, expect; mention seed, skip, and mocktail for dependencies.

How do you widget-test states without real network calls?

This tests UI isolation from I/O. Mock the repository with Mockito, stub methods to yield loading, success, and error, and inject it via constructor or provider. Avoid real HTTP calls or unmocked clients in widget tests.

How do you verify a Text widget with 'Hello' is present?

Find.text('Hello') locates the widget; expect(finder, findsOneWidget) asserts exactly one exists.

Unit, widget, and integration test differences in Flutter

Tests your grasp of Flutter's test pyramid and isolation levels. Unit tests check pure Dart logic; widget tests verify UI in a headless environment; integration tests exercise the full app on a device. Red flag: saying widget tests require an emulator.

What is Pigeon and how does it improve platform channels?

This tests type-safe platform channels versus manual MethodChannel boilerplate. Answer: Pigeon is a dev-time code generator that creates typed host stubs from a Dart contract, removing string keys and encoding. Red flag: calling it a runtime library.