[WIP] Add recipe to show Nav2 to Nav3 migration plan

app/build.gradle.kts

@@ -80,6 +80,7 @@ dependencies {
     implementation(libs.androidx.hilt.navigation.compose)
     implementation(libs.androidx.lifecycle.viewmodel.navigation3)
     implementation(libs.androidx.material.icons.extended)
+    implementation(libs.androidx.navigation2)
 
     implementation(libs.hilt.android)
     ksp(libs.hilt.compiler)

app/src/main/AndroidManifest.xml

@@ -90,6 +90,14 @@
             android:exported="true"
             android:label="@string/app_name"
             android:theme="@style/Theme.Nav3Recipes"/>
+        <activity
+            android:name=".migration.start.MainActivity"
+            android:exported="true"
+            android:theme="@style/Theme.Nav3Recipes"/>
+        <activity
+            android:name=".migration.step1.MainActivity"
+            android:exported="true"
+            android:theme="@style/Theme.Nav3Recipes"/>
     </application>
 
 </manifest>

app/src/main/java/com/example/nav3recipes/migration/start/MainActivity.kt

@@ -0,0 +1,70 @@
+/*
+ * Copyright 2025 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 com.example.nav3recipes.migration.start
+
+import android.os.Bundle
+import androidx.activity.ComponentActivity
+import androidx.activity.compose.setContent
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.padding
+import androidx.compose.material3.Button
+import androidx.compose.material3.Scaffold
+import androidx.compose.material3.Text
+import androidx.compose.ui.Modifier
+import androidx.navigation.compose.NavHost
+import androidx.navigation.compose.composable
+import androidx.navigation.compose.rememberNavController
+import androidx.navigation.toRoute
+import com.example.nav3recipes.ui.setEdgeToEdgeConfig
+import kotlinx.serialization.Serializable
+
+/**
+ * Basic Navigation2 example with two screens. This will be the starting point for migration to
+ * Navigation 3.
+ */
+
+@Serializable
+private data object RouteA
+
+@Serializable
+private data class RouteB(val id: String)
+
+class MainActivity : ComponentActivity() {
+
+    override fun onCreate(savedInstanceState: Bundle?) {
+        setEdgeToEdgeConfig()
+        super.onCreate(savedInstanceState)
+        setContent {
+            val navController = rememberNavController()
+            Scaffold { paddingValues ->
+                NavHost(navController = navController, startDestination = RouteA, modifier = Modifier.padding(paddingValues)) {
+                    composable<RouteA> {
+                        Column {
+                            Text("Route A")
+                            Button(onClick = { navController.navigate(route = RouteB(id = "123")) }) {
+                                Text("Go to B")
+                            }
+                        }
+                    }
+                    composable<RouteB> { key ->
+                        Text("Route B: ${key.toRoute<RouteB>().id}")
+                    }
+                }
+            }
+        }
+    }
+}

app/src/main/java/com/example/nav3recipes/migration/step1/MainActivity.kt

@@ -0,0 +1,125 @@
+/*
+ * Copyright 2025 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 com.example.nav3recipes.migration.step1
+
+import android.os.Bundle
+import androidx.activity.ComponentActivity
+import androidx.activity.compose.setContent
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.padding
+import androidx.compose.material3.Button
+import androidx.compose.material3.Scaffold
+import androidx.compose.material3.Text
+import androidx.compose.runtime.mutableStateListOf
+import androidx.compose.runtime.remember
+import androidx.compose.ui.Modifier
+import androidx.navigation.NavHostController
+import androidx.navigation.compose.NavHost
+import androidx.navigation.compose.composable
+import androidx.navigation.compose.rememberNavController
+import androidx.navigation.toRoute
+import androidx.navigation3.runtime.NavEntry
+import androidx.navigation3.runtime.entryProvider
+import androidx.navigation3.ui.NavDisplay
+import com.example.nav3recipes.ui.setEdgeToEdgeConfig
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Job
+import kotlinx.coroutines.launch
+import kotlinx.serialization.Serializable
+
+/**
+ * Basic Navigation2 example with two screens. This will be the starting point for migration to
+ * Navigation 3.
+ */
+
+@Serializable
+private data object RouteA
+
+@Serializable
+private data class RouteB(val id: String)
+
+class MainActivity : ComponentActivity() {
+
+    override fun onCreate(savedInstanceState: Bundle?) {
+        setEdgeToEdgeConfig()
+        super.onCreate(savedInstanceState)
+        setContent {
+            val navController = rememberNavController()
+            val nav3Navigator = remember { Nav3NavigatorSimple(navController) }
+
+            Scaffold { paddingValues ->
+                NavDisplay(
+                    backStack = nav3Navigator.backStack,
+                    entryProvider = entryProvider(fallback = { key ->
+                        println("Key $key not handled by entryProvider, using fallback")
+                        NavEntry(key = key) {
+                            NavHost(
+                                navController = navController,
+                                startDestination = RouteA,
+                                modifier = Modifier.padding(paddingValues)
+                            ) {
+                                composable<RouteA> {
+                                    Column {
+                                        Text("Route A")
+                                        Button(onClick = { navController.navigate(route = RouteB(id = "123")) }) {
+                                            Text("Go to B")
+                                        }
+                                    }
+                                }
+                                composable<RouteB> { key ->
+                                    Text("Route B: ${key.toRoute<RouteB>().id}")
+                                }
+                            }
+                        }
+                    }
+                ) {
+                    // Empty entryProvider
+                })
+            }
+        }
+    }
+}
+
+class Nav3NavigatorSimple(val navController: NavHostController){
+
+    val coroutineScope = CoroutineScope(Job())
+
+    // We need a single element to avoid "backStack cannot be empty" error b/430023647
+    val backStack = mutableStateListOf<Any>(Unit)
+
+    init {
+        coroutineScope.launch {
+            navController.currentBackStack.collect { nav2BackStack ->
+                with(backStack) {
+                    if (nav2BackStack.isNotEmpty()){
+                        clear()
+                        val entriesToAdd = nav2BackStack.mapNotNull { entry ->
+                            // Ignore nav graph root entries
+                            if (entry.destination::class.qualifiedName == "androidx.navigation.compose.ComposeNavGraphNavigator.ComposeNavGraph"){
+                                null
+                            } else {
+                                entry
+                            }
+                        }
+                        addAll(entriesToAdd)
+                    }
+                }
+            }
+        }
+    }
+}
+

gradle/libs.versions.toml

@@ -14,21 +14,22 @@
 
 [versions]
 agp = "8.10.1"
-kotlin = "2.2.0-RC2"
-kotlinSerialization = "2.1.21"
+kotlin = "2.2.0"
+kotlinSerialization = "2.2.0"
 coreKtx = "1.16.0"
 junit = "4.13.2"
 junitVersion = "1.2.1"
 espressoCore = "3.6.1"
-kotlinxSerializationCore = "1.8.1"
+kotlinxSerializationCore = "1.9.0"
 lifecycleRuntimeKtx = "2.9.1"
 lifecycleViewmodel = "1.0.0-SNAPSHOT"
 activityCompose = "1.12.0-alpha02"
 composeBom = "2025.06.00"
+navigation2 = "2.9.1"
 navigation3 = "1.0.0-alpha04"
 material3 = "1.4.0-alpha15"
 nav3Material = "1.0.0-SNAPSHOT"
-ksp = "2.2.0-RC2-2.0.1"
+ksp = "2.2.0-2.0.2"
 hilt = "2.56.2"
 hiltNavigationCompose = "1.2.0"
 
@@ -51,6 +52,7 @@ androidx-material3-windowsizeclass = { group = "androidx.compose.material3", nam
 androidx-adaptive-layout = { group = "androidx.compose.material3.adaptive", name = "adaptive-layout" }
 androidx-hilt-navigation-compose         = { module = "androidx.hilt:hilt-navigation-compose", version.ref = "hiltNavigationCompose" }
 androidx-lifecycle-viewmodel-navigation3 = { module = "androidx.lifecycle:lifecycle-viewmodel-navigation3", version.ref = "lifecycleViewmodel" }
+androidx-navigation2 = { module = "androidx.navigation:navigation-compose", version.ref = "navigation2" }
 androidx-navigation3-runtime = { module = "androidx.navigation3:navigation3-runtime", version.ref = "navigation3" }
 androidx-navigation3-ui = { module = "androidx.navigation3:navigation3-ui", version.ref = "navigation3" }
 hilt-android = { group = "com.google.dagger", name = "hilt-android", version.ref = "hilt" }