Free Jetpack Compose Interview Questions

Recomposition, state, side effects, and Compose performance.

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What actually triggers a recomposition in Jetpack Compose?
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Why does hoisting state make a composable more reusable, and what is the standard hoisting shape?
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What is the difference between remember and rememberSaveable, and when does each survive?
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What are the three phases of a Compose frame, and why does the distinction matter?
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What makes a composable function skippable versus restartable?
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Why can an unstable parameter type prevent a composable from being skipped?
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What is the difference between the Stable and Immutable annotations, and what contract do you promise?
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Why does passing a lambda to a composable sometimes break skipping, and how do you fix it?
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When does derivedStateOf actually help, and when is it pointless?
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In a LazyColumn, what does providing a stable key per item change, and what breaks without it?
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What is the purpose of the key composable, and how is it different from a LazyColumn item key?
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Why is capturing a changing value inside LaunchedEffect(Unit) a bug, and what are the two correct fixes?
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What exactly do the keys of a LaunchedEffect control?
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How does rememberUpdatedState differ from just passing a value as a LaunchedEffect key?
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What is DisposableEffect for, and what is the consequence of forgetting onDispose?
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When should you use SideEffect versus LaunchedEffect?
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What does produceState do that a LaunchedEffect plus a MutableState does not?
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What problem does snapshotFlow solve, and what is a common misuse?
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What is the difference between mutableStateOf holding a List and using mutableStateListOf?
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Does Modifier order matter, and can you give a case where reordering changes behavior?
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Why prefer passing a lambda to Modifier.offset or graphicsLayer instead of the value-taking overload?
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What is the difference between a static and a dynamic CompositionLocal, and what is the cost of each?
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When is CompositionLocal the right tool versus just drilling a parameter?
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What is the difference between Modifier.composed and the Modifier.Node API, and why is the newer one preferred?
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In a custom Layout, what are the rules around measuring children and calling place?
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Why is SubcomposeLayout more expensive than Layout, and when is it justified?
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How far does a recomposition propagate when a single state changes?
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Why can reading a state high in the tree cause the whole subtree to recompose, and how do you narrow the scope?
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What goes wrong when you use an unstable key with remember?
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How should a ViewModel expose state to Compose, and what is the tradeoff between StateFlow and Compose State?
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Why should you not create or remember a ViewModel with remember instead of the viewModel or hiltViewModel functions?
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In Navigation Compose, where should screen state live, and what is hoisted versus retained?
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How are arguments passed and typed in Navigation Compose, and why avoid passing complex objects?
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How do you read recomposition counts to find performance problems, and what does a high count mean?
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What do the Compose compiler metrics tell you, and how do you act on them?
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In Compose UI tests, why do you often need waitForIdle or to control mainClock, and what does autoAdvance do?
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How do finders like onNodeWithText work, and why is the semantics tree, not the visual tree, what tests query?
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What is the risk of doing heavy work directly in the body of a composable, and where should it go instead?
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Why must composable functions be free of side effects and safe to run in any order or skip entirely?
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What is the difference between collectAsState and collectAsStateWithLifecycle, and when does it matter?
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How does interop work when embedding a Compose UI in a View hierarchy and vice versa, and what lifecycle concern arises?
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Why can AndroidView's update block over-run, and how do you keep it efficient?
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What does it mean that Compose animations are state-driven, and how does this affect recomposition cost?
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Why might a Composable that reads a MutableState still not recompose when you expect it to?
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What is the difference between structural and referential equality policies for mutableStateOf, and when would you change it?
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How does a custom Saver enable rememberSaveable for a non-trivial type, and what are the two directions it defines?
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Why can a lambda captured in a remember block become stale, and how does that differ from rememberUpdatedState?
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What is donut-hole skipping, and how does passing content lambdas enable it?
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Why does deferring a state read into a lambda passed to a child sometimes eliminate recomposition of the parent entirely?
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How do the snapshot system's isolation and atomicity let Compose run composition off the main thread safely?
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