Recipe: Keep UI state across rotation and the back stack

Problem: scroll position, a half-typed field, an expanded/collapsed toggle — you want it to survive rotation and back-stack navigation, and sometimes process death too.

Pick the API based on how durable the value must be:

API	Survives rotation + back stack	Survives process death	Needs Parcelable/Saver
remember	❌	❌	–
rememberRetained	✅*	❌	no
rememberSaveable	✅*	✅	yes
rememberRetainedSaveable	✅*	✅	yes

* Back stack survival requires NavigableCircuitContent, which gives each record its own state registry. CircuitContent alone does not offer a back stack to survive.

@Composable
override fun present(): EditorState {
  // Transient — fine to lose on rotation.
  var focusedField by remember { mutableStateOf<Field?>(null) }

  // Survives rotation + back stack, no serialization. Good default for most UI state.
  var expanded by rememberRetained { mutableStateOf(false) }

  // Also survives process death; needs a Saveable type (String is fine).
  var draft by rememberRetainedSaveable { mutableStateOf("") }

  // …
}

How to choose:

• remember — cheap, transient state you don’t mind recomputing (focus, a transient highlight).
• rememberRetained — survives rotation and back-stack navigation by keeping the value in memory; no Parcelable needed. Use for selections, expanded states, and computed values you don’t want to recompute.
• rememberSaveable — survives process death by serializing to instance state. Needs a Parcelable or custom Saver.
• rememberRetainedSaveable — keeps the value in memory like rememberRetained, and also saves it so the value can be restored after process death.

For primitives, use the boxing-free holders: rememberRetained { mutableIntStateOf(0) }, mutableLongStateOf, etc.

Warning

Retain values, not lifecycle-beholden objects like Flow, Navigator, or Context; those can keep too much or leak across the back stack. To get data from a Flow into retained state safely, see observing a Flow.

See also: Retention reference · Observe a Flow