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/*
* Copyright 2021 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package androidx.compose.runtime.saveable
import androidx.compose.runtime.Composable
import androidx.compose.runtime.MutableState
import androidx.compose.runtime.RememberObserver
import androidx.compose.runtime.SideEffect
import androidx.compose.runtime.SnapshotMutationPolicy
import androidx.compose.runtime.currentCompositeKeyHash
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.neverEqualPolicy
import androidx.compose.runtime.referentialEqualityPolicy
import androidx.compose.runtime.remember
import androidx.compose.runtime.snapshots.SnapshotMutableState
import androidx.compose.runtime.structuralEqualityPolicy
/**
* 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).
*
* @sample androidx.compose.runtime.saveable.samples.RememberSaveable
*
* 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.
*
* @sample androidx.compose.runtime.saveable.samples.RememberSaveableCustomSaver
*
* You can use it with a value stored inside [androidx.compose.runtime.mutableStateOf].
*
* @sample androidx.compose.runtime.saveable.samples.RememberSaveableWithMutableState
*
* 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.
*
* @sample androidx.compose.runtime.saveable.samples.RememberSaveableWithMutableStateAndCustomSaver
*
* @param inputs A set of inputs such that, when any of them have changed, will cause the state to
* reset and [init] to be rerun
* @param saver The [Saver] object which defines how the state is saved and restored.
* @param key An optional key to be used as a key for the saved value. If not provided we use the
* automatically generated by the Compose runtime which is unique for the every exact code location
* in the composition tree
* @param init A factory function to create the initial value of this state
*/
@Composable
fun rememberSaveable(
vararg inputs: Any?,
saver: Saver = autoSaver(),
key: String? = null,
init: () -> T
): T {
val compositeKey = currentCompositeKeyHash
// key is the one provided by the user or the one generated by the compose runtime
val finalKey = if (!key.isNullOrEmpty()) {
key
} else {
compositeKey.toString(MaxSupportedRadix)
}
@Suppress("UNCHECKED_CAST")
(saver as Saver)
val registry = LocalSaveableStateRegistry.current
val holder = remember {
// value is restored using the registry or created via [init] lambda
val restored = registry?.consumeRestored(finalKey)?.let {
saver.restore(it)
}
val finalValue = restored ?: init()
SaveableHolder(saver, registry, finalKey, finalValue, inputs)
}
val value = holder.getValueIfInputsDidntChange(inputs) ?: init()
SideEffect {
holder.update(saver, registry, finalKey, value, inputs)
}
return value
}
/**
* 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.
*
* @sample androidx.compose.runtime.saveable.samples.RememberSaveableWithMutableStateAndCustomSaver
*
* @param inputs A set of inputs such that, when any of them have changed, will cause the state to
* reset and [init] to be rerun
* @param stateSaver The [Saver] object which defines how the value inside the MutableState is
* saved and restored.
* @param key An optional key to be used as a key for the saved value. If not provided we use the
* automatically generated by the Compose runtime which is unique for the every exact code location
* in the composition tree
* @param init A factory function to create the initial value of this state
*/
@Composable
fun rememberSaveable(
vararg inputs: Any?,
stateSaver: Saver,
key: String? = null,
init: () -> MutableState
): MutableState = rememberSaveable(
*inputs,
saver = mutableStateSaver(stateSaver),
key = key,
init = init
)
private class SaveableHolder(
private var saver: Saver,
private var registry: SaveableStateRegistry?,
private var key: String,
private var value: T,
private var inputs: Array
) : SaverScope, RememberObserver {
private var entry: SaveableStateRegistry.Entry? = null
/**
* Value provider called by the registry.
*/
private val valueProvider = {
with(saver) {
save(requireNotNull(value) { "Value should be initialized" })
}
}
fun update(
saver: Saver,
registry: SaveableStateRegistry?,
key: String,
value: T,
inputs: Array
) {
var entryIsOutdated = false
if (this.registry !== registry) {
this.registry = registry
entryIsOutdated = true
}
if (this.key != key) {
this.key = key
entryIsOutdated = true
}
this.saver = saver
this.value = value
this.inputs = inputs
if (entry != null && entryIsOutdated) {
entry?.unregister()
entry = null
register()
}
}
private fun register() {
val registry = registry
require(entry == null) { "entry($entry) is not null" }
if (registry != null) {
registry.requireCanBeSaved(valueProvider())
entry = registry.registerProvider(key, valueProvider)
}
}
override fun canBeSaved(value: Any): Boolean {
val registry = registry
return registry == null || registry.canBeSaved(value)
}
override fun onRemembered() {
register()
}
override fun onForgotten() {
entry?.unregister()
}
override fun onAbandoned() {
entry?.unregister()
}
fun getValueIfInputsDidntChange(inputs: Array): T? {
return if (inputs.contentEquals(this.inputs)) {
value
} else {
null
}
}
}
@Suppress("UNCHECKED_CAST")
private fun mutableStateSaver(inner: Saver) = with(inner as Saver) {
Saver, MutableState>(
save = { state ->
require(state is SnapshotMutableState) {
"If you use a custom MutableState implementation you have to write a custom " +
"Saver and pass it as a saver param to rememberSaveable()"
}
val saved = save(state.value)
if (saved != null) {
mutableStateOf(saved, state.policy as SnapshotMutationPolicy)
} else {
// if the inner saver returned null we need to return null as well so the
// user's init lambda will be used instead of restoring mutableStateOf(null)
null
}
},
restore = @Suppress("UNCHECKED_CAST", "ExceptionMessage") {
require(it is SnapshotMutableState)
mutableStateOf(
if (it.value != null) restore(it.value!!) else null,
it.policy as SnapshotMutationPolicy
) as MutableState
}
)
}
private fun SaveableStateRegistry.requireCanBeSaved(value: Any?) {
if (value != null && !canBeSaved(value)) {
throw IllegalArgumentException(
if (value is SnapshotMutableState<*>) {
if (value.policy !== neverEqualPolicy() &&
value.policy !== structuralEqualityPolicy() &&
value.policy !== referentialEqualityPolicy()
) {
"If you use a custom SnapshotMutationPolicy for your MutableState you have to" +
" write a custom Saver"
} else {
"MutableState containing ${value.value} cannot be saved using the current " +
"SaveableStateRegistry. The default implementation only supports types " +
"which can be stored inside the Bundle. Please consider implementing a " +
"custom Saver for this class and pass it as a stateSaver parameter to " +
"rememberSaveable()."
}
} else {
generateCannotBeSavedErrorMessage(value)
}
)
}
}
internal fun generateCannotBeSavedErrorMessage(value: Any): String =
"$value cannot be saved using the current SaveableStateRegistry. The default " +
"implementation only supports types which can be stored inside the Bundle" +
". Please consider implementing a custom Saver for this class and pass it" +
" to rememberSaveable()."
/**
* The maximum radix available for conversion to and from strings.
*/
private val MaxSupportedRadix = 36
