WIP RetainedStateHolder

circuit-foundation/src/commonMain/kotlin/com/slack/circuit/foundation/CircuitContent.kt

@@ -37,28 +37,7 @@ public fun CircuitContent(
   unavailableContent: (@Composable (screen: Screen, modifier: Modifier) -> Unit) =
     circuit.onUnavailableContent,
 ) {
-  val navigator =
-    remember(onNavEvent) {
-      object : Navigator {
-        override fun goTo(screen: Screen) {
-          onNavEvent(NavEvent.GoTo(screen))
-        }
-
-        override fun resetRoot(newRoot: Screen): List<Screen> {
-          onNavEvent(NavEvent.ResetRoot(newRoot))
-          return emptyList()
-        }
-
-        override fun pop(): Screen? {
-          onNavEvent(NavEvent.Pop)
-          return null
-        }
-
-        override fun peek(): Screen {
-          return screen
-        }
-      }
-    }
+  val navigator = remember(onNavEvent) { Navigator.navEventNavigator(screen, onNavEvent) }
   CircuitContent(screen, navigator, modifier, circuit, unavailableContent)
 }
 

circuit-foundation/src/commonMain/kotlin/com/slack/circuit/foundation/NavEvent.kt

@@ -19,6 +19,31 @@ public fun Navigator.onNavEvent(event: NavEvent) {
   }
 }
 
+public fun Navigator.Companion.navEventNavigator(
+  screen: Screen,
+  onNavEvent: (event: NavEvent) -> Unit,
+): Navigator {
+  return object : Navigator {
+    override fun goTo(screen: Screen) {
+      onNavEvent(NavEvent.GoTo(screen))
+    }
+
+    override fun resetRoot(newRoot: Screen): List<Screen> {
+      onNavEvent(NavEvent.ResetRoot(newRoot))
+      return emptyList()
+    }
+
+    override fun pop(): Screen? {
+      onNavEvent(NavEvent.Pop)
+      return null
+    }
+
+    override fun peek(): Screen {
+      return screen
+    }
+  }
+}
+
 /** A sealed navigation interface intended to be used when making a navigation callback. */
 public sealed interface NavEvent : CircuitUiEvent {
   /** Corresponds to [Navigator.pop]. */

circuit-runtime/src/commonMain/kotlin/com/slack/circuit/runtime/Navigator.kt

@@ -43,6 +43,8 @@ public interface Navigator {
 
     override fun resetRoot(newRoot: Screen): List<Screen> = emptyList()
   }
+
+  public companion object
 }
 
 /** Calls [Navigator.pop] until the given [predicate] is matched or it pops the root. */

samples/star/src/commonMain/kotlin/com/slack/circuit/star/home/HomeScreen.kt

@@ -15,13 +15,18 @@ import androidx.compose.runtime.Composable
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
+import androidx.compose.runtime.saveable.rememberSaveableStateHolder
 import androidx.compose.runtime.setValue
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.graphics.Color
 import com.slack.circuit.codegen.annotations.CircuitInject
 import com.slack.circuit.foundation.CircuitContent
+import com.slack.circuit.foundation.LocalCircuit
 import com.slack.circuit.foundation.NavEvent
+import com.slack.circuit.foundation.navEventNavigator
 import com.slack.circuit.foundation.onNavEvent
+import com.slack.circuit.foundation.rememberPresenter
+import com.slack.circuit.foundation.rememberUi
 import com.slack.circuit.retained.rememberRetained
 import com.slack.circuit.runtime.CircuitUiEvent
 import com.slack.circuit.runtime.CircuitUiState
@@ -70,6 +75,7 @@ fun HomePresenter(navigator: Navigator): HomeScreen.State {
 @Composable
 fun HomeContent(state: HomeScreen.State, modifier: Modifier = Modifier) {
   var contentComposed by rememberRetained { mutableStateOf(false) }
+
   Scaffold(
     modifier = modifier.fillMaxWidth(),
     contentWindowInsets = WindowInsets(0, 0, 0, 0),
@@ -82,13 +88,29 @@ fun HomeContent(state: HomeScreen.State, modifier: Modifier = Modifier) {
       }
     },
   ) { paddingValues ->
+    val saveableStateHolder = rememberSaveableStateHolder()
+    val currentScreen = state.navItems[state.selectedIndex].screen
+    saveableStateHolder.SaveableStateProvider(currentScreen) {
+      val circuit = requireNotNull(LocalCircuit.current)
+      val ui = rememberUi(currentScreen, factory = circuit::ui)
+      val presenter =
+        rememberPresenter(
+          currentScreen,
+          navigator =
+            Navigator.navEventNavigator(currentScreen) { event ->
+              state.eventSink(ChildNav(event))
+            },
+          factory = circuit::presenter,
+        )
+
+      CircuitContent(
+        screen = currentScreen,
+        modifier = Modifier.padding(paddingValues),
+        presenter = presenter!!,
+        ui = ui!!,
+      )
+    }
     contentComposed = true
-    val screen = state.navItems[state.selectedIndex].screen
-    CircuitContent(
-      screen,
-      modifier = Modifier.padding(paddingValues),
-      onNavEvent = { event -> state.eventSink(ChildNav(event)) },
-    )
   }
   Platform.ReportDrawnWhen { contentComposed }
 }