SavedStateHandleSupport.kt
/*
* 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.
*/
@file:JvmName("SavedStateHandleSupport")
package androidx.lifecycle
import android.os.Bundle
import androidx.annotation.MainThread
import androidx.lifecycle.ViewModelProvider.NewInstanceFactory.Companion.VIEW_MODEL_KEY
import androidx.lifecycle.viewmodel.CreationExtras
import androidx.savedstate.SavedStateRegistry
import androidx.savedstate.SavedStateRegistryOwner
private const val VIEWMODEL_KEY = "androidx.lifecycle.internal.SavedStateHandlesVM"
/**
* Enables the support of [SavedStateHandle] in a component.
*
* After this method, [createSavedStateHandle] can be called on [CreationExtras] containing this
* [SavedStateRegistryOwner] / [ViewModelStoreOwner].
*
* Must be called while component is in `INITIALIZED` or `CREATED` state and before
* a [ViewModel] with [SavedStateHandle] is requested.
*/
@MainThread
fun <T> T.enableSavedStateHandles()
where T : SavedStateRegistryOwner, T : ViewModelStoreOwner {
val currentState = lifecycle.currentState
require(
currentState == Lifecycle.State.INITIALIZED || currentState == Lifecycle.State.CREATED
)
// make sure that SavedStateHandlesVM is created.
ViewModelProvider(this, object : ViewModelProvider.Factory {
override fun <T : ViewModel> create(modelClass: Class<T>): T {
@Suppress("UNCHECKED_CAST")
return SavedStateHandlesVM() as T
}
})[VIEWMODEL_KEY, SavedStateHandlesVM::class.java]
savedStateRegistry.runOnNextRecreation(SavedStateHandleAttacher::class.java)
}
private fun createSavedStateHandle(
savedStateRegistryOwner: SavedStateRegistryOwner,
viewModelStoreOwner: ViewModelStoreOwner,
key: String,
defaultArgs: Bundle?
): SavedStateHandle {
val vm = viewModelStoreOwner.savedStateHandlesVM
val savedStateRegistry = savedStateRegistryOwner.savedStateRegistry
val handle = SavedStateHandle.createHandle(
savedStateRegistry.consumeRestoredStateForKey(key), defaultArgs
)
val controller = SavedStateHandleController(key, handle)
controller.attachToLifecycle(savedStateRegistry, savedStateRegistryOwner.lifecycle)
vm.controllers.add(controller)
return handle
}
/**
* Creates `SavedStateHandle` that can be used in your ViewModels
*
* This function requires `this.installSavedStateHandleSupport()` call during the component
* initialization. Latest versions of androidx components like `ComponentActivity`, `Fragment`,
* `NavBackStackEntry` makes this call automatically.
*
* This [CreationExtras] must contain [SAVED_STATE_REGISTRY_OWNER_KEY],
* [VIEW_MODEL_STORE_OWNER_KEY] and [VIEW_MODEL_KEY].
*
* @throws IllegalArgumentException if this `CreationExtras` are missing required keys:
* `ViewModelStoreOwnerKey`, `SavedStateRegistryOwnerKey`, `VIEW_MODEL_KEY`
*/
@MainThread
public fun CreationExtras.createSavedStateHandle(): SavedStateHandle {
val savedStateRegistryOwner = this[SAVED_STATE_REGISTRY_OWNER_KEY]
?: throw IllegalArgumentException(
"CreationExtras must have a value by `SAVED_STATE_REGISTRY_OWNER_KEY`"
)
val viewModelStateRegistryOwner = this[VIEW_MODEL_STORE_OWNER_KEY]
?: throw IllegalArgumentException(
"CreationExtras must have a value by `VIEW_MODEL_STORE_OWNER_KEY`"
)
val defaultArgs = this[DEFAULT_ARGS_KEY]
val key = this[VIEW_MODEL_KEY] ?: throw IllegalArgumentException(
"CreationExtras must have a value by `VIEW_MODEL_KEY`"
)
return createSavedStateHandle(
savedStateRegistryOwner, viewModelStateRegistryOwner, key, defaultArgs
)
}
internal object ThrowingFactory : ViewModelProvider.Factory {
override fun <T : ViewModel> create(modelClass: Class<T>): T {
throw IllegalStateException(
"enableSavedStateHandles() wasn't called " +
"prior to createSavedStateHandle() call"
)
}
}
internal val ViewModelStoreOwner.savedStateHandlesVM: SavedStateHandlesVM
get() =
ViewModelProvider(this, ThrowingFactory)[VIEWMODEL_KEY, SavedStateHandlesVM::class.java]
internal class SavedStateHandlesVM : ViewModel() {
val controllers = mutableListOf<SavedStateHandleController>()
}
// it reconnects existent SavedStateHandles to SavedStateRegistryOwner when it is recreated
internal class SavedStateHandleAttacher : SavedStateRegistry.AutoRecreated {
override fun onRecreated(owner: SavedStateRegistryOwner) {
if (owner !is ViewModelStoreOwner) {
throw java.lang.IllegalStateException(
"Internal error: SavedStateHandleAttacher should be registered only on components" +
"that implement ViewModelStoreOwner"
)
}
val viewModelStore = (owner as ViewModelStoreOwner).viewModelStore
// if savedStateHandlesVM wasn't created previously, we shouldn't trigger a creation of it
if (!viewModelStore.keys().contains(VIEWMODEL_KEY)) return
owner.savedStateHandlesVM.controllers.forEach {
it.attachToLifecycle(owner.savedStateRegistry, owner.lifecycle)
}
owner.savedStateRegistry.runOnNextRecreation(SavedStateHandleAttacher::class.java)
}
}
/**
* A key for [SavedStateRegistryOwner] that corresponds to [ViewModelStoreOwner]
* of a [ViewModel] that is being created.
*/
@JvmField
val SAVED_STATE_REGISTRY_OWNER_KEY = object : CreationExtras.Key<SavedStateRegistryOwner> {}
/**
* A key for [ViewModelStoreOwner] that is an owner of a [ViewModel] that is being created.
*/
@JvmField
val VIEW_MODEL_STORE_OWNER_KEY = object : CreationExtras.Key<ViewModelStoreOwner> {}
/**
* A key for default arguments that should be passed to [SavedStateHandle] if needed.
*/
@JvmField
val DEFAULT_ARGS_KEY = object : CreationExtras.Key<Bundle> {}