androidx.compose.runtime.saveable

fun SaveableStateRegistry(
    restoredValues: Map<String, List<Any?>>?,
    canBeSaved: (Any) -> Boolean
): SaveableStateRegistry

Creates SaveableStateRegistry.

fun <Original : Any?, Saveable : Any> Saver(
    save: SaverScope.(value) -> Saveable?,
    restore: (value) -> Original?
): Saver<Original, Saveable>

The Saver describes how the object of Original class can be simplified and converted into something which is Saveable.

What types can be saved is defined by SaveableStateRegistry, by default everything which can be stored in the Bundle class can be saved. The implementations can check that the provided value can be saved via SaverScope.canBeSaved

You can pass the implementations of this class as a parameter for rememberSaveable.

import androidx.compose.runtime.saveable.Saver

data class Holder(var value: Int)

// this Saver implementation converts Holder object which we don't know how to save
// to Int which we can save
val HolderSaver = Saver<Holder, Int>(save = { it.value }, restore = { Holder(it) })

fun <T : Any?> autoSaver(): Saver<T, Any>

The default implementation of Saver which does not perform any conversion.

It is used by rememberSaveable by default.

fun <Original : Any?, Saveable : Any?> listSaver(
    save: SaverScope.(value) -> List<Saveable>,
    restore: (list: List<Saveable>) -> Original?
): Saver<Original, Any>

The Saver implementation which allows to represent your Original class as a list of Saveable values.

What types can be saved is defined by SaveableStateRegistry, by default everything which can be stored in the Bundle class can be saved.

You can use it as a parameter for rememberSaveable.

import androidx.compose.runtime.saveable.Saver
import androidx.compose.runtime.saveable.listSaver

data class Size(val x: Int, val y: Int)

val sizeSaver =
    listSaver<Size, Int>(save = { listOf(it.x, it.y) }, restore = { Size(it[0], it[1]) })

fun <T : Any?> mapSaver(save: SaverScope.(value) -> Map<String, Any?>, restore: (Map<String, Any?>) -> T?): Saver<T, Any>

The Saver implementation which allows to represent your class as a map of values which can be saved individually.

What types can be saved is defined by SaveableStateRegistry, by default everything which can be stored in the Bundle class can be saved.

You can use it as a parameter for rememberSaveable.

import androidx.compose.runtime.saveable.Saver
import androidx.compose.runtime.saveable.mapSaver

data class User(val name: String, val age: Int)

val userSaver = run {
    val nameKey = "Name"
    val ageKey = "Age"
    mapSaver(
        save = { mapOf(nameKey to it.name, ageKey to it.age) },
        restore = { User(it[nameKey] as String, it[ageKey] as Int) }
    )
}

@Composable
fun <T : Any> rememberSaveable(
    vararg inputs: Any?,
    saver: Saver<T, Any> = autoSaver(),
    key: String? = null,
    init: () -> T
): T

Remember the value produced by init.

It behaves similarly to remember, but the stored value will survive the activity or process recreation using the saved instance state mechanism (for example it happens when the screen is rotated in the Android application).

import androidx.compose.runtime.saveable.rememberSaveable

val list = rememberSaveable { mutableListOf<Int>() }

If you use it with types which can be stored inside the Bundle then it will be saved and restored automatically using autoSaver, otherwise you will need to provide a custom Saver implementation via the saver param.

import androidx.compose.runtime.saveable.Saver
import androidx.compose.runtime.saveable.rememberSaveable

val holder = rememberSaveable(saver = HolderSaver) { Holder(0) }

You can use it with a value stored inside androidx.compose.runtime.mutableStateOf.

import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.saveable.rememberSaveable

var value by rememberSaveable { mutableStateOf(({ "value" })()) }

If the value inside the MutableState can be stored inside the Bundle it would be saved and restored automatically, otherwise you will need to provide a custom Saver implementation via an overload with which has stateSaver param.

import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.saveable.Saver
import androidx.compose.runtime.saveable.rememberSaveable

val holder = rememberSaveable(stateSaver = HolderSaver) { mutableStateOf(Holder(0)) }

@Composable
fun <T : Any?> rememberSaveable(
    vararg inputs: Any?,
    stateSaver: Saver<T, Any>,
    key: String? = null,
    init: () -> MutableState<T>
): MutableState<T>

Remember the value produced by init.

It behaves similarly to remember, but the stored value will survive the activity or process recreation using the saved instance state mechanism (for example it happens when the screen is rotated in the Android application).

Use this overload if you remember a mutable state with a type which can't be stored in the Bundle so you have to provide a custom saver object.

import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.saveable.Saver
import androidx.compose.runtime.saveable.rememberSaveable

val holder = rememberSaveable(stateSaver = HolderSaver) { mutableStateOf(Holder(0)) }

@Composable
fun rememberSaveableStateHolder(): SaveableStateHolder

Creates and remembers the instance of SaveableStateHolder.

val LocalSaveableStateRegistry: ProvidableCompositionLocal<SaveableStateRegistry?>

CompositionLocal with a current SaveableStateRegistry instance.