kotlin-flow-state-event-modeling

For a single consumer handling exactly-once events, use a Channel(Channel.BUFFERED) exposed via receiveAsFlow() instead of a default MutableSharedFlow. Default SharedFlow has no replay buffer, so events emitted with no active collector are lost.

Use StateFlow when state always has a value and is read both by collectors and synchronous .value code. Use SharedFlow for hot streams with multiple subscribers where synchronous reads are not required, and configure replay explicitly.

SharingStarted.WhileSubscribed disconnects the upstream when no collectors are active, so .value returns the last cached or initial value. If .value must stay fresh without collectors, use SharingStarted.Eagerly or explicit initialization.

Use MutableStateFlow.update { current -> ... } instead of reading .value and writing it back. The update function applies the transform atomically against the latest state, preventing lost updates from concurrent modifications.

Each call to stateIn() launches a new sharing coroutine on the given scope that never completes, so repeated calls leak coroutines and duplicate work. Assign the result to a val property so the shared instance is computed once.

Model absence explicitly with a nullable type, a sealed interface UI state, or Result, or use phase initialization where the StateFlow is only exposed after the real value loads. Sentinels force consumers to treat fake data as real domain values.