| /* |
| * Copyright 2020 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.savedinstancestate |
| |
| import androidx.compose.runtime.Composable |
| import androidx.compose.runtime.CompositionLifecycleObserver |
| import androidx.compose.runtime.ExperimentalComposeApi |
| import androidx.compose.runtime.MutableState |
| import androidx.compose.runtime.currentComposer |
| import androidx.compose.runtime.remember |
| |
| /** |
| * 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.savedinstancestate.samples.RememberSavedInstanceStateSample |
| * |
| * This function works nicely with mutable objects, when you update the state of this object |
| * instead of recreating it. If you work with immutable objects [savedInstanceState] can suit you |
| * more as it wraps the value into the [MutableState]. |
| * |
| * 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.savedinstancestate.samples.CustomSaverSample |
| * |
| * @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 |
| */ |
| @OptIn(ExperimentalComposeApi::class) |
| @Composable |
| fun <T : Any> rememberSavedInstanceState( |
| vararg inputs: Any?, |
| saver: Saver<T, out Any> = autoSaver(), |
| key: String? = null, |
| init: () -> T |
| ): T { |
| val finalKey = if (!key.isNullOrEmpty()) { |
| key |
| } else { |
| currentComposer.currentCompoundKeyHash.toString() |
| } |
| val registry = UiSavedStateRegistryAmbient.current |
| val valueProvider = remember(*inputs) { ValueProvider<T>() } |
| return valueProvider.updateAndReturnValue(registry, saver, finalKey, init) |
| } |
| |
| private class ValueProvider<T : Any> : SaverScope, CompositionLifecycleObserver { |
| |
| private var registry: UiSavedStateRegistry? = null |
| private var saver: Saver<T, out Any>? = null |
| private var key: String? = null |
| private var value: T? = null |
| |
| @Suppress("UNCHECKED_CAST") |
| private fun saver(): Saver<T, Any> = (saver as Saver<T, Any>) |
| |
| fun updateAndReturnValue( |
| registry: UiSavedStateRegistry?, |
| saver: Saver<T, out Any>, |
| key: String, |
| init: () -> T |
| ): T { |
| val oldRegistry = this.registry |
| val oldKey = this.key |
| this.saver = saver |
| this.registry = registry |
| this.key = key |
| val value = value ?: run { |
| // TODO not restore when the input values changed (use hashKeys?) b/152014032 |
| val restored = registry?.consumeRestored(key)?.let { |
| saver().restore(it) |
| } |
| val result = restored ?: init() |
| this.value = result |
| result |
| } |
| if (oldRegistry !== registry || oldKey != key) { |
| oldRegistry?.unregisterProvider(oldKey!!) |
| registry?.registerProvider(key) { |
| val result = with(saver()) { save(value) } |
| if (result != null) { |
| check(registry.canBeSaved(result)) |
| } |
| result |
| } |
| } |
| return value |
| } |
| |
| override fun canBeSaved(value: Any) = registry!!.canBeSaved(value) |
| |
| override fun onLeave() { |
| registry?.unregisterProvider(key!!) |
| } |
| |
| override fun onEnter() { |
| // no-op |
| } |
| } |