Performance & Best Practices

A checklist for keeping an advanced Compose app fast and correct.

Compose performance

Minimize recomposition scope. Read state as low in the tree as possible so only small composables recompose.
Use stable types. Prefer immutable data classes and List (not MutableList) as composable parameters; unstable types force recomposition.
Key your lists. Provide key = { it.id } in LazyColumn items.
Hoist remember correctly. Expensive computations go in remember(key) { ... }, not in the composable body.
Avoid backwards writes. Do not write to state you have already read in the same composition.
derivedStateOf for state computed from other state, to avoid extra recompositions.

Threading

Never block the main thread. Wrap blocking I/O in withContext(Dispatchers.IO).
Use viewModelScope / lifecycleScope so work is cancelled with its owner.
Collect flows with collectAsStateWithLifecycle() so collection stops when the UI is not visible.

Memory and leaks

Do not hold Context/Activity/View references in a ViewModel.
Cancel coroutines and unregister listeners (DisposableEffect) when scopes end.
Prefer applicationContext for long-lived needs.

App size and startup

Enable R8/minification and resource shrinking for release builds.
Defer heavy initialization off the startup path.

A pre-release checklist

No blocking work on the main thread
Lists use stable keys and items are stable
State is hoisted; recomposition scopes are small
ViewModels hold no View/Context
Coroutines use lifecycle-aware scopes
Release build minified and tested
Unit + Compose tests green in CI

The worked example

examples/android/ brings the architecture together: a ViewModel exposing an immutable StateFlow UI state, a repository behind an interface, navigation, and JVM unit tests — all building in CI. The Room, Hilt, Retrofit, and WorkManager chapters above provide drop-in code to extend it.

Exercises

Audit a screen for unnecessary recompositions (use the Layout Inspector / recomposition counts).
Move a blocking call into withContext(Dispatchers.IO) and confirm the UI stays responsive.

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