Interview questions in Mobile Dev, page 19
How task cancellation works with async/await
Cancellation is a flag, not a kill; check Task.isCancelled or call checkCancellation, URLSession throws CancellationError automatically.
Explain FutureBuilder and how it manages async UI states
This tests declarative async UI state management. Obtain the Future before build, pass it to FutureBuilder, and branch on snapshot.connectionState and hasError to render loading, data, or error states.
What are Room's three main components and their functions?
Tests whether you know Room's architectural layers. Name the three: Database holds config and is the access point; Entity represents a table schema; DAO defines SQL operations. Red flag: confusing DAOs with Repositories or claiming Room is a full ORM.
Animated API versus Reanimated architecture
Animated declares animations that the native driver runs, but logic and gestures cross the bridge; Reanimated runs worklets directly on the UI thread.
What is an actor and how does it prevent data races
Actors serialize access to mutable state, reachable only via await; compiler blocks unsafe access. Token-refresh actor coalesces concurrent refreshes.
Purpose of factory fromJson constructor in Dart models
Factory fromJson centralizes deserialization, preprocesses Map values before instantiation, and keeps the primary constructor clean.
Why choose DataStore over SharedPreferences for a toggle?
This tests your grasp of modern Android storage safety beyond syntax. A strong answer names DataStore's async coroutines API, type safety, transactions, and migration support. A red flag is claiming SharedPreferences is simpler while ignoring ANR risk.
Shared values and useAnimatedStyle in Reanimated
UseSharedValue holds a mutable .value readable on both threads, useAnimatedStyle derives styles as a worklet, mutate .value with withTiming or withSpring.
Implicit .animation() vs explicit withAnimation
.animation(value:) animates a view when a tracked value changes; withAnimation wraps the state mutation so all dependent views animate.
Describe a robust error handling strategy for network requests
Tests whether you classify failures by layer rather than catching everything generically. Inspect DioExceptionType for connectivity, check HTTP status before parsing, and isolate JSON decode errors. Never show the same message for timeouts and 500s.
How do you define a Room table for a Kotlin data class?
Tests your grasp of the minimum Room entity contract. A strong answer cites Entity and PrimaryKey, notes Kotlin defaults work out of the box, and mentions ColumnInfo for renaming.
Animated.event for scroll-driven parallax
Animated.event maps an event path to an Animated.Value, wire it to onScroll with useNativeDriver, then interpolate the value for header transform.
Add shadow and rounded corners to a UIView
CornerRadius needs masksToBounds true, but that clips the shadow; set shadowPath to keep both and stay performant.
Compare manual JSON serialization versus json_serializable
It tests build automation versus manual control in Dart serialization. Manual methods avoid build steps but risk drift; code generation cuts boilerplate but adds compile latency. Claiming code gen slows runtime or that manual is always simpler.
How do you add a non-null column with a default in Room?
Bump version; run ALTER TABLE ADD COLUMN with NOT NULL DEFAULT in a Migration; register via addMigrations.
What is a worklet in Reanimated
A worklet is a JS function marked to run on the UI thread runtime with a captured snapshot of its scope, enabling synchronous per-frame work.
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.
Shared element transitions with Reanimated
Wrap both views in Animated.View with the same sharedTransitionTag, use a native-stack navigator so Reanimated interpolates between source and target.
We are hiring for this. Every open role lists the topics its interview covers, so you can prepare for the real thing rather than guessing.
See open roles