[Owl] Migrates to navigation-compose

Owl/app/build.gradle

@@ -80,6 +80,7 @@ dependencies {
     implementation Libs.Kotlin.stdlib
 
     implementation Libs.AndroidX.coreKtx
+    implementation Libs.AndroidX.navigation
 
     implementation Libs.AndroidX.Compose.runtime
     implementation Libs.AndroidX.Compose.foundation

Owl/app/src/main/java/com/example/owl/ui/NavGraph.kt

@@ -16,37 +16,26 @@
 
 package com.example.owl.ui
 
-import android.os.Parcelable
-import androidx.compose.runtime.Immutable
-import com.example.owl.ui.utils.Navigator
-import kotlinx.android.parcel.Parcelize
+import androidx.navigation.NavHostController
+import androidx.navigation.compose.navigate
 
-/**
- * Models the screens in the app and any arguments they require.
- */
-sealed class Destination : Parcelable {
-    @Parcelize
-    object Onboarding : Destination()
-
-    @Parcelize
-    object Courses : Destination()
-
-    @Immutable
-    @Parcelize
-    data class Course(val courseId: Long) : Destination()
+object Destinations {
+    const val Onboarding = "Onboarding_dest_key"
+    const val Courses = "Courses_dest_key"
+    const val CourseDetails = "Courses_dest_key"
 }
 
 /**
  * Models the navigation actions in the app.
  */
-class Actions(navigator: Navigator<Destination>) {
+class Actions(navController: NavHostController) {
     val onboardingComplete: () -> Unit = {
-        navigator.navigate(Destination.Courses)
+        navController.navigate(Destinations.Courses)
     }
     val selectCourse: (Long) -> Unit = { courseId: Long ->
-        navigator.navigate(Destination.Course(courseId))
+        navController.navigate(Destinations.CourseDetails + "/$courseId")
     }
     val upPress: () -> Unit = {
-        navigator.back()
+        navController.popBackStack()
     }
 }

Owl/app/src/main/java/com/example/owl/ui/OwlApp.kt

@@ -17,38 +17,40 @@
 package com.example.owl.ui
 
 import androidx.activity.OnBackPressedDispatcher
-import androidx.compose.animation.Crossfade
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.Providers
 import androidx.compose.runtime.remember
-import androidx.compose.runtime.savedinstancestate.rememberSavedInstanceState
+import androidx.navigation.compose.NavHost
+import androidx.navigation.compose.composable
+import androidx.navigation.compose.rememberNavController
 import com.example.owl.ui.course.CourseDetails
 import com.example.owl.ui.courses.Courses
 import com.example.owl.ui.onboarding.Onboarding
 import com.example.owl.ui.utils.AmbientBackDispatcher
-import com.example.owl.ui.utils.Navigator
 import com.example.owl.ui.utils.ProvideDisplayInsets
 import com.example.owl.ui.utils.ProvideImageLoader
 
 @Composable
 fun OwlApp(backDispatcher: OnBackPressedDispatcher) {
-    @Suppress("RemoveExplicitTypeArguments")
-    val navigator: Navigator<Destination> = rememberSavedInstanceState(
-        saver = Navigator.saver<Destination>(backDispatcher)
-    ) {
-        Navigator(Destination.Onboarding, backDispatcher)
-    }
-    val actions = remember(navigator) { Actions(navigator) }
 
     Providers(AmbientBackDispatcher provides backDispatcher) {
         ProvideDisplayInsets {
             ProvideImageLoader {
-                Crossfade(navigator.current) { destination ->
-                    when (destination) {
-                        Destination.Onboarding -> Onboarding(actions.onboardingComplete)
-                        Destination.Courses -> Courses(actions.selectCourse)
-                        is Destination.Course -> CourseDetails(
-                            destination.courseId,
+                val navController = rememberNavController()
+
+                val actions = remember(navController) { Actions(navController) }
+                NavHost(navController = navController, startDestination = Destinations.Onboarding) {
+                    composable(Destinations.Onboarding) {
+                        Onboarding(actions.onboardingComplete)
+                    }
+                    composable(Destinations.Courses) {
+                        Courses(actions.selectCourse)
+                    }
+                    composable(Destinations.CourseDetails + "/{courseId}") { backStackEntry ->
+                        val courseId = backStackEntry.arguments?.getLong("courseId")
+                            ?: throw IllegalArgumentException("No course ID provided")
+                        CourseDetails(
+                            courseId,
                             actions.selectCourse,
                             actions.upPress
                         )

Owl/app/src/main/java/com/example/owl/ui/utils/Navigation.kt

@@ -16,61 +16,12 @@
 
 package com.example.owl.ui.utils
 
-import android.os.Parcelable
 import androidx.activity.OnBackPressedCallback
 import androidx.activity.OnBackPressedDispatcher
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.onCommit
 import androidx.compose.runtime.remember
-import androidx.compose.runtime.savedinstancestate.listSaver
 import androidx.compose.runtime.staticAmbientOf
-import androidx.compose.runtime.toMutableStateList
-
-/**
- * A simple navigator which maintains a back stack.
- */
-class Navigator<T : Parcelable> private constructor(
-    initialBackStack: List<T>,
-    backDispatcher: OnBackPressedDispatcher
-) {
-    constructor(
-        initial: T,
-        backDispatcher: OnBackPressedDispatcher
-    ) : this(listOf(initial), backDispatcher)
-
-    private val backStack = initialBackStack.toMutableStateList()
-    private val backCallback = object : OnBackPressedCallback(canGoBack()) {
-        override fun handleOnBackPressed() {
-            back()
-        }
-    }.also { callback ->
-        backDispatcher.addCallback(callback)
-    }
-    val current: T get() = backStack.last()
-
-    fun back() {
-        backStack.removeAt(backStack.lastIndex)
-        backCallback.isEnabled = canGoBack()
-    }
-
-    fun navigate(destination: T) {
-        backStack += destination
-        backCallback.isEnabled = canGoBack()
-    }
-
-    private fun canGoBack(): Boolean = backStack.size > 1
-
-    companion object {
-        /**
-         * Serialize the back stack to save to instance state.
-         */
-        fun <T : Parcelable> saver(backDispatcher: OnBackPressedDispatcher) =
-            listSaver<Navigator<T>, T>(
-                save = { navigator -> navigator.backStack.toList() },
-                restore = { backstack -> Navigator(backstack, backDispatcher) }
-            )
-    }
-}
 
 /**
  * An effect for handling presses of the device back button.

Owl/buildSrc/src/main/java/com/example/owl/buildsrc/Dependencies.kt

@@ -45,6 +45,7 @@ object Libs {
 
     object AndroidX {
         const val coreKtx = "androidx.core:core-ktx:1.5.0-alpha04"
+        const val navigation = "androidx.navigation:navigation-compose:1.0.0-alpha01"
 
         object Compose {
             const val snapshot = ""