kmp-compose-state-container

Use remember for ephemeral UI state like dropdown toggles, rememberSaveable for form input that must survive rotation, and ViewModel for business data or async operations. The decision depends on what must survive recomposition, config changes, and process death.

Write a custom Saver that maps your type to Bundle-safe primitives, then pass it via rememberSaveable(stateSaver = yourSaver). The Saver defines save and restore lambdas converting between your type and a Map of primitives.

Config-change survival behavior of rememberSaveable and ViewModel applies only on Android. On Desktop and iOS, composable lifetime is tied to the window or view lifecycle, so plan state survival accordingly for cross-platform needs.

Bundles have a size limit around 1 MB, and storing large collections triggers TransactionTooLargeException on Android. Store only IDs in rememberSaveable or SavedStateHandle and reload the actual data from a repository or cache.

Scope the ViewModel to a nav graph by obtaining the graph's back-stack entry with navController.getBackStackEntry and passing it as the viewModelStoreOwner to koinViewModel. The ViewModel then survives navigation between screens within that graph.

A LaunchedEffect(Unit) captures the lambda value at launch time, so recompositions with a new lambda are ignored. Wrap the lambda with rememberUpdatedState and call the current reference inside the effect to always use the latest value.