rememberUpdatedState

Functions summary

State<T>
@Composable
<T : Any?> rememberUpdatedState(newValue: T)

remember a mutableStateOf and update its value to newValue on each recomposition of the rememberUpdatedState call.
Cmn

Functions

rememberUpdatedState

Cmn 
@Composable
fun <T : Any?> rememberUpdatedState(newValue: T): State<T>

remember a mutableStateOf and update its value to newValue on each recomposition of the rememberUpdatedState call.

rememberUpdatedState should be used when parameters or values computed during composition are referenced by a long-lived lambda or object expression. Recomposition will update the resulting State without recreating the long-lived lambda or object, allowing that object to persist without cancelling and resubscribing, or relaunching a long-lived operation that may be expensive or prohibitive to recreate and restart. This may be common when working with DisposableEffect or LaunchedEffect, for example:

import androidx.compose.runtime.Composable
import androidx.compose.runtime.DisposableEffect
import androidx.compose.runtime.remember
import androidx.compose.runtime.rememberUpdatedState

@Composable
fun EventHandler(dispatcher: Dispatcher, onEvent: () -> Unit) {
    val currentOnEvent by rememberUpdatedState(onEvent)

    // Event handlers are ordered and a new onEvent should not cause us to re-register,
    // losing our position in the dispatcher.
    DisposableEffect(dispatcher) {
        val disposable =
            dispatcher.addListener {
                // currentOnEvent will always refer to the latest onEvent function that
                // the EventHandler was recomposed with
                currentOnEvent()
            }
        onDispose { disposable.dispose() }
    }
}

LaunchedEffects often describe state machines that should not be reset and restarted if a parameter or event callback changes, but they should have the current value available when needed. For example:

import androidx.compose.runtime.Composable
import androidx.compose.runtime.LaunchedEffect
import androidx.compose.runtime.remember
import androidx.compose.runtime.rememberUpdatedState

@Composable
fun NotificationHost(state: NotificationState, onTimeout: (Notification) -> Unit) {
    val currentOnTimeout by rememberUpdatedState(onTimeout)

    state.currentNotification?.let { currentNotification ->
        LaunchedEffect(currentNotification) {
            // We should not restart this delay if onTimeout changes, but we want to call
            // the onTimeout we were last recomposed with when it completes.
            delay(NotificationTimeout)
            currentOnTimeout(currentNotification)
        }
    }

    // ...
}

By using rememberUpdatedState a composable function can update these operations in progress.