Retain instances

decompose/src/main/java/com/arkivanov/decompose/ComponentContext.kt

@@ -1,11 +1,7 @@
 package com.arkivanov.decompose
 
-import androidx.activity.OnBackPressedDispatcher
-import androidx.lifecycle.Lifecycle
+import androidx.activity.OnBackPressedDispatcherOwner
+import androidx.lifecycle.LifecycleOwner
+import androidx.lifecycle.ViewModelStoreOwner
 
-interface ComponentContext : RouterFactory {
-
-    val lifecycle: Lifecycle
-    val savedStateKeeper: SavedStateKeeper
-    val onBackPressedDispatcher: OnBackPressedDispatcher
-}
+interface ComponentContext : RouterFactory, SavedStateKeeperOwner, LifecycleOwner, OnBackPressedDispatcherOwner, ViewModelStoreOwner

decompose/src/main/java/com/arkivanov/decompose/ComponentContextExt.kt

@@ -4,11 +4,13 @@ import androidx.lifecycle.Lifecycle
 
 fun ComponentContext.child(key: String, lifecycle: Lifecycle = this.lifecycle): ComponentContext {
     val childSavedStateKeeper = savedStateKeeper.child(key)
+    val childViewModelStore = viewModelStore.child(key)
 
     return ComponentContextImpl(
         lifecycle,
         savedStateKeeper = childSavedStateKeeper,
         onBackPressedDispatcher = onBackPressedDispatcher,
-        routerFactory = DefaultRouterFactory(lifecycle, childSavedStateKeeper, onBackPressedDispatcher)
+        viewModelStore = childViewModelStore,
+        routerFactory = DefaultRouterFactory(lifecycle, childSavedStateKeeper, onBackPressedDispatcher, childViewModelStore)
     )
 }

decompose/src/main/java/com/arkivanov/decompose/ComponentContextImpl.kt

@@ -2,10 +2,19 @@ package com.arkivanov.decompose
 
 import androidx.activity.OnBackPressedDispatcher
 import androidx.lifecycle.Lifecycle
+import androidx.lifecycle.ViewModelStore
 
 internal class ComponentContextImpl(
-    override val lifecycle: Lifecycle,
+    private val lifecycle: Lifecycle,
     override val savedStateKeeper: SavedStateKeeper,
-    override val onBackPressedDispatcher: OnBackPressedDispatcher,
+    private val onBackPressedDispatcher: OnBackPressedDispatcher,
+    private val viewModelStore: ViewModelStore,
     routerFactory: RouterFactory
-) : ComponentContext, RouterFactory by routerFactory
+) : ComponentContext, RouterFactory by routerFactory {
+
+    override fun getLifecycle(): Lifecycle = lifecycle
+
+    override fun getOnBackPressedDispatcher(): OnBackPressedDispatcher = onBackPressedDispatcher
+
+    override fun getViewModelStore(): ViewModelStore = viewModelStore
+}

decompose/src/main/java/com/arkivanov/decompose/DefaultRouterFactory.kt

@@ -3,11 +3,13 @@ package com.arkivanov.decompose
 import android.os.Parcelable
 import androidx.activity.OnBackPressedDispatcher
 import androidx.lifecycle.Lifecycle
+import androidx.lifecycle.ViewModelStore
 
 internal class DefaultRouterFactory(
     private val lifecycle: Lifecycle,
     private val savedStateKeeper: SavedStateKeeper,
-    private val onBackPressedDispatcher: OnBackPressedDispatcher
+    private val onBackPressedDispatcher: OnBackPressedDispatcher,
+    private val viewModelStore: ViewModelStore
 ) : RouterFactory {
 
     override fun <C : Parcelable> router(
@@ -22,16 +24,18 @@ internal class DefaultRouterFactory(
             configurationClassLoader = configurationClassLoader,
             lifecycle = lifecycle,
             savedStateKeeper = savedStateKeeper,
-            savedStateKey = key,
-            onBackPressedDispatcher = onBackPressedDispatcher.takeIf { handleBackButton }
-        ) { configuration, lifecycle, savedStateKeeper ->
+            key = key,
+            onBackPressedDispatcher = onBackPressedDispatcher.takeIf { handleBackButton },
+            viewModelStore = viewModelStore
+        ) { configuration, lifecycle, savedStateKeeper, viewModelStore ->
             componentFactory(
                 configuration,
                 ComponentContextImpl(
                     lifecycle,
                     savedStateKeeper,
                     onBackPressedDispatcher,
-                    DefaultRouterFactory(lifecycle, savedStateKeeper, onBackPressedDispatcher)
+                    viewModelStore,
+                    DefaultRouterFactory(lifecycle, savedStateKeeper, onBackPressedDispatcher, viewModelStore)
                 )
             )
         }

decompose/src/main/java/com/arkivanov/decompose/LifecycleExt.kt

@@ -3,6 +3,7 @@ package com.arkivanov.decompose
 import androidx.lifecycle.DefaultLifecycleObserver
 import androidx.lifecycle.Lifecycle
 import androidx.lifecycle.LifecycleOwner
+import androidx.lifecycle.LifecycleRegistry
 
 internal inline fun Lifecycle.doOnDestroy(crossinline block: () -> Unit) {
     addObserver(
@@ -13,3 +14,47 @@ internal inline fun Lifecycle.doOnDestroy(crossinline block: () -> Unit) {
         }
     )
 }
+
+internal fun LifecycleRegistry.create() {
+    if (currentState == Lifecycle.State.INITIALIZED) {
+        handleLifecycleEvent(Lifecycle.Event.ON_CREATE)
+    }
+}
+
+internal fun LifecycleRegistry.start() {
+    create()
+
+    if (currentState == Lifecycle.State.CREATED) {
+        handleLifecycleEvent(Lifecycle.Event.ON_START)
+    }
+}
+
+internal fun LifecycleRegistry.resume() {
+    start()
+
+    if (currentState == Lifecycle.State.STARTED) {
+        handleLifecycleEvent(Lifecycle.Event.ON_RESUME)
+    }
+}
+
+internal fun LifecycleRegistry.pause() {
+    if (currentState == Lifecycle.State.RESUMED) {
+        handleLifecycleEvent(Lifecycle.Event.ON_PAUSE)
+    }
+}
+
+internal fun LifecycleRegistry.stop() {
+    pause()
+
+    if (currentState == Lifecycle.State.STARTED) {
+        handleLifecycleEvent(Lifecycle.Event.ON_STOP)
+    }
+}
+
+internal fun LifecycleRegistry.destroy() {
+    stop()
+
+    if (currentState == Lifecycle.State.CREATED) {
+        handleLifecycleEvent(Lifecycle.Event.ON_DESTROY)
+    }
+}

decompose/src/main/java/com/arkivanov/decompose/RootComponentBuilder.kt

@@ -4,30 +4,35 @@ import androidx.activity.OnBackPressedDispatcher
 import androidx.activity.OnBackPressedDispatcherOwner
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.remember
+import androidx.lifecycle.ViewModelStore
+import androidx.lifecycle.ViewModelStoreOwner
 import androidx.savedstate.SavedStateRegistry
 import androidx.savedstate.SavedStateRegistryOwner
 
 @Composable
 fun RootComponent(
     savedStateRegistry: SavedStateRegistry,
     onBackPressedDispatcher: OnBackPressedDispatcher,
+    viewModelStore: ViewModelStore,
     factory: (ComponentContext) -> Component
 ) {
     val lifecycle = lifecycle()
 
     val component =
         remember {
             val savedStateKeeper = rootSavedStateKeeper(savedStateRegistry)
-            val routerFactory = DefaultRouterFactory(lifecycle, savedStateKeeper, onBackPressedDispatcher)
-            factory(ComponentContextImpl(lifecycle, savedStateKeeper, onBackPressedDispatcher, routerFactory))
+            val routerFactory = DefaultRouterFactory(lifecycle, savedStateKeeper, onBackPressedDispatcher, viewModelStore)
+            factory(ComponentContextImpl(lifecycle, savedStateKeeper, onBackPressedDispatcher, viewModelStore, routerFactory))
         }
 
     component.content()
 }
 
 @Composable
-fun <T> T.RootComponent(factory: (ComponentContext) -> Component) where T : SavedStateRegistryOwner, T : OnBackPressedDispatcherOwner {
-    RootComponent(savedStateRegistry, onBackPressedDispatcher, factory)
+fun <T> T.RootComponent(
+    factory: (ComponentContext) -> Component
+) where T : SavedStateRegistryOwner, T : OnBackPressedDispatcherOwner, T : ViewModelStoreOwner {
+    RootComponent(savedStateRegistry, onBackPressedDispatcher, viewModelStore, factory)
 }
 
 private fun rootSavedStateKeeper(registry: SavedStateRegistry): SavedStateKeeper =

decompose/src/main/java/com/arkivanov/decompose/RouterImpl.kt

@@ -8,16 +8,18 @@ import androidx.compose.runtime.Composable
 import androidx.compose.runtime.mutableStateOf
 import androidx.lifecycle.Lifecycle
 import androidx.lifecycle.LifecycleOwner
-import androidx.lifecycle.LifecycleRegistry
+import androidx.lifecycle.ViewModel
+import androidx.lifecycle.ViewModelStore
 
 internal class RouterImpl<C : Parcelable>(
     initialConfiguration: C,
     private val configurationClassLoader: ClassLoader?,
     private val lifecycle: Lifecycle,
     private val savedStateKeeper: SavedStateKeeper,
-    private val savedStateKey: String,
+    private val key: String,
     onBackPressedDispatcher: OnBackPressedDispatcher?,
-    private val componentFactory: (C, Lifecycle, SavedStateKeeper) -> Component
+    viewModelStore: ViewModelStore,
+    private val componentFactory: (C, Lifecycle, SavedStateKeeper, ViewModelStore) -> Component
 ) : Router<C>, LifecycleOwner {
 
     private val onBackPressedCallback = OnBackPressedCallbackImpl()
@@ -26,15 +28,37 @@ internal class RouterImpl<C : Parcelable>(
         onBackPressedDispatcher?.addCallback(this, onBackPressedCallback)
     }
 
+    private val viewModel = viewModelStore.viewModel(key) { ViewModelImpl<C>() }
     private val stackState = mutableStateOf(restoreState() ?: Stack(active = createComponent(initialConfiguration)))
 
     init {
-        savedStateKeeper.register(savedStateKey, ::saveState)
-        lifecycle.doOnDestroy { savedStateKeeper.unregister(savedStateKey) }
+        savedStateKeeper.register(key, ::saveState)
 
         updateOnBackPressedCallback()
 
+        viewModel.activeEntry = stackState.value.active
         stackState.value.active.lifecycleHolder.registry.resume()
+
+        lifecycle.doOnDestroy(::destroy)
+    }
+
+    private fun destroy() {
+        savedStateKeeper.unregister(key)
+
+        val stack = stackState.value
+
+        stack.active.lifecycleHolder.registry.destroy()
+
+        stack.backStack.reversed().forEach { entry ->
+            when (entry) {
+                is Stack.Entry.Created -> {
+                    entry.viewModelStore.clear()
+                    entry.lifecycleHolder.registry.destroy()
+                }
+
+                is Stack.Entry.Destroyed -> Unit
+            }.let {}
+        }
     }
 
     override val stackSize: Int get() = stackState.value.backStack.size + 1
@@ -51,7 +75,7 @@ internal class RouterImpl<C : Parcelable>(
     override fun getLifecycle(): Lifecycle = lifecycle
 
     private fun restoreState(): Stack<C>? {
-        val savedState = savedStateKeeper.consume(savedStateKey) ?: return null
+        val savedState = savedStateKeeper.consume(key) ?: return null
 
         val configurations =
             savedState
@@ -61,7 +85,8 @@ internal class RouterImpl<C : Parcelable>(
 
         val last = configurations.last()
         val lastBundle: Bundle? = savedState.getBundle(last.toString())
-        val lastEntry: Stack.Entry.Created<C> = createComponent(last, lastBundle)
+        val lastViewModelStore = viewModel.activeEntry?.viewModelStore
+        val lastEntry: Stack.Entry.Created<C> = createComponent(last, lastBundle, lastViewModelStore)
 
         val backStack =
             configurations.dropLast(1).map {
@@ -96,40 +121,33 @@ internal class RouterImpl<C : Parcelable>(
 
         val savedEntry: Stack.Entry.Created<C> = oldStack.active.let { it.copy(savedState = it.savedStateKeeper.save()) }
 
-        savedEntry.lifecycleHolder.registry.apply {
-            handleLifecycleEvent(Lifecycle.Event.ON_PAUSE)
-        }
-
+        savedEntry.lifecycleHolder.registry.pause()
         newEntry.lifecycleHolder.registry.resume()
+        savedEntry.lifecycleHolder.registry.stop()
 
-        savedEntry.lifecycleHolder.registry.apply {
-            handleLifecycleEvent(Lifecycle.Event.ON_STOP)
-        }
-
+        viewModel.activeEntry = newEntry
         stackState.value = oldStack.copy(active = newEntry, backStack = oldStack.backStack + savedEntry)
 
         updateOnBackPressedCallback()
     }
 
-    private fun LifecycleRegistry.resume() {
-        if (currentState == Lifecycle.State.INITIALIZED) {
-            handleLifecycleEvent(Lifecycle.Event.ON_CREATE)
-        }
-        handleLifecycleEvent(Lifecycle.Event.ON_START)
-        handleLifecycleEvent(Lifecycle.Event.ON_RESUME)
-    }
-
-    private fun createComponent(configuration: C, savedState: Bundle? = null): Stack.Entry.Created<C> {
+    private fun createComponent(
+        configuration: C,
+        savedState: Bundle? = null,
+        savedViewModelStore: ViewModelStore? = null
+    ): Stack.Entry.Created<C> {
         val componentLifecycleHolder = LifecycleHolder()
         val mergedLifecycle = MergedLifecycle(lifecycle, componentLifecycleHolder.registry)
         val savedStateKeeper = DefaultSavedStateKeeper(savedState)
-        val component = componentFactory(configuration, mergedLifecycle.lifecycle, savedStateKeeper)
+        val viewModelStore = savedViewModelStore ?: ViewModelStore()
+        val component = componentFactory(configuration, mergedLifecycle.lifecycle, savedStateKeeper, viewModelStore)
 
         return Stack.Entry.Created(
             configuration = configuration,
             component = component,
             lifecycleHolder = componentLifecycleHolder,
-            savedStateKeeper = savedStateKeeper
+            savedStateKeeper = savedStateKeeper,
+            viewModelStore = viewModelStore
         )
     }
 
@@ -147,17 +165,12 @@ internal class RouterImpl<C : Parcelable>(
 
         val topEntry: Stack.Entry.Created<C> = oldStack.active
 
-        topEntry.lifecycleHolder.registry.apply {
-            handleLifecycleEvent(Lifecycle.Event.ON_PAUSE)
-        }
-
+        topEntry.lifecycleHolder.registry.handleLifecycleEvent(Lifecycle.Event.ON_PAUSE)
         nextActiveEntry.lifecycleHolder.registry.resume()
+        topEntry.viewModelStore.clear()
+        topEntry.lifecycleHolder.registry.destroy()
 
-        topEntry.lifecycleHolder.registry.apply {
-            handleLifecycleEvent(Lifecycle.Event.ON_STOP)
-            handleLifecycleEvent(Lifecycle.Event.ON_DESTROY)
-        }
-
+        viewModel.activeEntry = nextActiveEntry
         stackState.value = oldStack.copy(active = nextActiveEntry, backStack = oldStack.backStack.dropLast(1))
 
         updateOnBackPressedCallback()
@@ -167,7 +180,7 @@ internal class RouterImpl<C : Parcelable>(
         onBackPressedCallback.isEnabled = stackState.value.backStack.isNotEmpty()
     }
 
-    private data class Stack<out C : Parcelable>(
+    internal data class Stack<out C : Parcelable>(
         val active: Entry.Created<C>,
         val backStack: List<Entry<C>> = emptyList()
     ) {
@@ -180,7 +193,8 @@ internal class RouterImpl<C : Parcelable>(
                 override val savedState: Bundle? = null,
                 val component: Component,
                 val lifecycleHolder: LifecycleHolder,
-                val savedStateKeeper: DefaultSavedStateKeeper
+                val savedStateKeeper: DefaultSavedStateKeeper,
+                val viewModelStore: ViewModelStore
             ) : Entry<C>()
 
             data class Destroyed<out C : Parcelable>(
@@ -195,4 +209,14 @@ internal class RouterImpl<C : Parcelable>(
             pop()
         }
     }
+
+    private class ViewModelImpl<C : Parcelable> : ViewModel() {
+        var activeEntry: Stack.Entry.Created<C>? = null
+
+        override fun onCleared() {
+            activeEntry?.viewModelStore?.clear()
+
+            super.onCleared()
+        }
+    }
 }

decompose/src/main/java/com/arkivanov/decompose/SavedStateKeeperOwner.kt

@@ -0,0 +1,6 @@
+package com.arkivanov.decompose
+
+interface SavedStateKeeperOwner {
+
+    val savedStateKeeper: SavedStateKeeper
+}