| /* |
| * 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.navigation.compose |
| |
| import android.content.ContextWrapper |
| import androidx.activity.OnBackPressedDispatcherOwner |
| import androidx.compose.runtime.Composable |
| import androidx.compose.runtime.Providers |
| import androidx.compose.runtime.onCommit |
| import androidx.compose.runtime.remember |
| import androidx.compose.runtime.savedinstancestate.ExperimentalRestorableStateHolder |
| import androidx.compose.runtime.savedinstancestate.RestorableStateHolder |
| import androidx.compose.runtime.savedinstancestate.rememberRestorableStateHolder |
| import androidx.compose.ui.platform.ContextAmbient |
| import androidx.compose.ui.platform.LifecycleOwnerAmbient |
| import androidx.compose.ui.platform.ViewModelStoreOwnerAmbient |
| import androidx.compose.ui.viewinterop.viewModel |
| import androidx.lifecycle.SavedStateHandle |
| import androidx.lifecycle.ViewModel |
| import androidx.navigation.NavGraph |
| import androidx.navigation.NavGraphBuilder |
| import androidx.navigation.NavHostController |
| import java.util.UUID |
| |
| /** |
| * Provides in place in the Compose hierarchy for self contained navigation to occur. |
| * |
| * Once this is called, any Composable within the given [NavGraphBuilder] can be navigated to from |
| * the provided [navController]. |
| * |
| * @sample androidx.navigation.compose.samples.BasicNav |
| * |
| * @param id the id to set on the graph |
| * @param startDestination an object to identify a destination |
| * @param builder the builder used to construct the graph |
| */ |
| @Composable |
| public fun NavHost( |
| navController: NavHostController, |
| id: Int = 0, |
| startDestination: Any, |
| builder: NavGraphBuilder.() -> Unit |
| ) { |
| NavHost( |
| navController, |
| remember (id, startDestination, builder) { |
| navController.createGraph(id, startDestination, builder) |
| } |
| ) |
| } |
| |
| /** |
| * Provides in place in the Compose hierarchy for self contained navigation to occur. |
| * |
| * Once this is called, any Composable within the given [NavGraphBuilder] can be navigated to from |
| * the provided [navController]. |
| * |
| * @param navController the navController for this host |
| * @param graph the graph for this host |
| */ |
| @OptIn(ExperimentalRestorableStateHolder::class) |
| @Composable |
| internal fun NavHost(navController: NavHostController, graph: NavGraph) { |
| var context = ContextAmbient.current |
| val lifecycleOwner = LifecycleOwnerAmbient.current |
| val viewModelStore = ViewModelStoreOwnerAmbient.current.viewModelStore |
| |
| // on successful recompose we setup the navController with proper inputs |
| // after the first time, this will only happen again if one of the inputs changes |
| onCommit(navController, lifecycleOwner, viewModelStore) { |
| navController.setLifecycleOwner(lifecycleOwner) |
| navController.setViewModelStore(viewModelStore) |
| |
| // unwrap the context until we find an OnBackPressedDispatcherOwner |
| while (context is ContextWrapper) { |
| if (context is OnBackPressedDispatcherOwner) { |
| navController.setOnBackPressedDispatcher( |
| (context as OnBackPressedDispatcherOwner).onBackPressedDispatcher |
| ) |
| break |
| } |
| context = (context as ContextWrapper).baseContext |
| } |
| } |
| |
| onCommit(graph) { |
| navController.graph = graph |
| } |
| |
| val restorableStateHolder = rememberRestorableStateHolder<UUID>() |
| |
| // state from the navController back stack |
| val currentNavBackStackEntry = navController.currentBackStackEntryAsState().value |
| |
| // If the currentNavBackStackEntry is null, we have popped all of the destinations |
| // off of the navController back stack and have nothing to show. |
| if (currentNavBackStackEntry != null) { |
| val destination = currentNavBackStackEntry.destination |
| // If the destination is not a compose destination, (e.i. activity, dialog, view, etc) |
| // then we do nothing and rely on Navigation to show the proper destination |
| if (destination is ComposeNavigator.Destination) { |
| // while in the scope of the composable, we provide the navBackStackEntry as the |
| // ViewModelStoreOwner and LifecycleOwner |
| Providers( |
| ViewModelStoreOwnerAmbient provides currentNavBackStackEntry, |
| LifecycleOwnerAmbient provides currentNavBackStackEntry |
| ) { |
| restorableStateHolder.withRestorableState { |
| destination.content(currentNavBackStackEntry) |
| } |
| } |
| } |
| } |
| } |
| |
| @OptIn(ExperimentalRestorableStateHolder::class) |
| @Composable |
| private fun RestorableStateHolder<UUID>.withRestorableState(content: @Composable () -> Unit) { |
| val viewModel = viewModel<BackStackEntryIdViewModel>() |
| viewModel.restorableStateHolder = this |
| withRestorableState(viewModel.id, content) |
| } |
| |
| @OptIn(ExperimentalRestorableStateHolder::class) |
| internal class BackStackEntryIdViewModel(handle: SavedStateHandle) : ViewModel() { |
| |
| private val IdKey = "RestorableStateHolder_BackStackEntryKey" |
| |
| // we create our own id for each back stack entry to support multiple entries of the same |
| // destination. this id will be restored by SavedStateHandle |
| val id: UUID = handle.get<UUID>(IdKey) ?: UUID.randomUUID().also { handle.set(IdKey, it) } |
| |
| var restorableStateHolder: RestorableStateHolder<UUID>? = null |
| |
| // onCleared will be called on the entries removed from the back stack. here we notify |
| // RestorableStateHolder that we shouldn't save the state for this id, so when we open this |
| // destination again the state will not be restored. |
| override fun onCleared() { |
| super.onCleared() |
| restorableStateHolder?.removeState(id) |
| } |
| } |