Demonstrate KMP ViewModel on multiple screens

Fruitties/androidApp/build.gradle.kts

@@ -17,15 +17,16 @@ plugins {
     alias(libs.plugins.androidApplication)
     alias(libs.plugins.kotlinAndroid)
     alias(libs.plugins.compose.compiler)
+    alias(libs.plugins.kotlinxSerialization)
 }
 
 android {
     namespace = "com.example.fruitties.android"
-    compileSdk = 35
+    compileSdk = 36
     defaultConfig {
         applicationId = "com.example.fruitties.android"
         minSdk = 26
-        targetSdk = 35
+        targetSdk = 36
         versionCode = 1
         versionName = "1.0"
     }
@@ -79,4 +80,9 @@ dependencies {
     implementation(libs.androidx.paging.compose.android)
     implementation(libs.androidx.lifecycle.viewmodel.compose)
     debugImplementation(libs.compose.ui.tooling)
+    implementation(libs.androidx.navigation3.runtime)
+    implementation(libs.androidx.navigation3.ui)
+    implementation(libs.androidx.lifecycle.viewmodel.navigation3)
+    implementation(libs.androidx.material3.adaptive.navigation3)
+    implementation(libs.kotlinx.serialization.core)
 }

Fruitties/androidApp/src/main/java/com/example/fruitties/android/MainActivity.kt

@@ -23,8 +23,24 @@ import androidx.activity.enableEdgeToEdge
 import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Surface
+import androidx.compose.runtime.Composable
 import androidx.compose.ui.Modifier
+import androidx.navigation3.runtime.NavKey
+import androidx.navigation3.runtime.entry
+import androidx.navigation3.runtime.entryProvider
+import androidx.navigation3.runtime.rememberNavBackStack
+import androidx.navigation3.runtime.rememberSavedStateNavEntryDecorator
+import androidx.navigation3.ui.NavDisplay
+import androidx.navigation3.ui.rememberSceneSetupNavEntryDecorator
+import com.example.fruitties.android.ui.CartScreen
 import com.example.fruitties.android.ui.ListScreen
+import kotlinx.serialization.Serializable
+
+@Serializable
+data object ListScreenKey : NavKey
+
+@Serializable
+data object CartScreenKey : NavKey
 
 class MainActivity : ComponentActivity() {
     override fun onCreate(savedInstanceState: Bundle?) {
@@ -36,9 +52,42 @@ class MainActivity : ComponentActivity() {
                     modifier = Modifier.fillMaxSize(),
                     color = MaterialTheme.colorScheme.background,
                 ) {
-                    ListScreen()
+                    NavApp()
                 }
             }
         }
     }
 }
+
+@Composable
+fun NavApp() {
+    val backStack = rememberNavBackStack(ListScreenKey)
+
+    NavDisplay(
+        backStack = backStack,
+        entryDecorators = listOf(
+            rememberSceneSetupNavEntryDecorator(),
+            rememberSavedStateNavEntryDecorator(),
+//            java.lang.NoSuchMethodError: No virtual method getKey()Ljava/lang/Object; in class Landroidx/navigation3/runtime/NavEntry; or its super classes (declaration of 'androidx.navigation3.runtime.NavEntry'
+//            rememberViewModelStoreNavEntryDecorator(),
+        ),
+        onBack = { keysToRemove -> repeat(keysToRemove) { backStack.removeLastOrNull() } },
+        entryProvider = entryProvider {
+            entry<ListScreenKey> {
+                ListScreen(
+                    onClickViewCart = {
+                        backStack.add(CartScreenKey)
+                    },
+                )
+            }
+            entry<CartScreenKey> {
+                CartScreen(
+                    onNavBack = {
+                        backStack.clear()
+                        backStack.add(ListScreenKey)
+                    },
+                )
+            }
+        },
+    )
+}

Fruitties/androidApp/src/main/java/com/example/fruitties/android/ui/CartScreen.kt

@@ -0,0 +1,134 @@
+/*
+ * Copyright 2024 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
+ *
+ *     https://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.fruitties.android.ui
+
+import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.WindowInsets
+import androidx.compose.foundation.layout.WindowInsetsSides
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.only
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.safeDrawing
+import androidx.compose.foundation.layout.systemBars
+import androidx.compose.foundation.layout.windowInsetsBottomHeight
+import androidx.compose.foundation.lazy.LazyColumn
+import androidx.compose.foundation.lazy.items
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.automirrored.filled.ArrowBack
+import androidx.compose.material3.CenterAlignedTopAppBar
+import androidx.compose.material3.ExperimentalMaterial3Api
+import androidx.compose.material3.Icon
+import androidx.compose.material3.IconButton
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Scaffold
+import androidx.compose.material3.Text
+import androidx.compose.material3.TopAppBarColors
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.collectAsState
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.remember
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.platform.LocalContext
+import androidx.compose.ui.res.stringResource
+import androidx.compose.ui.unit.dp
+import androidx.lifecycle.viewmodel.compose.viewModel
+import com.example.fruitties.android.R
+import com.example.fruitties.android.di.App
+import com.example.fruitties.viewmodel.CartViewModel
+
+@OptIn(ExperimentalMaterial3Api::class)
+@Composable
+fun CartScreen(onNavBack: () -> Unit) {
+    // Instantiate a ViewModel with a dependency on the AppContainer.
+    // To make ViewModel compatible with KMP, the ViewModel factory must
+    // create an instance without referencing the Android Application.
+    // Here we put the KMP-compatible AppContainer into the extras
+    // so it can be passed to the ViewModel factory.
+    val app = LocalContext.current.applicationContext as App
+    val extras = remember(app) {
+        val container = app.container
+        CartViewModel.newCreationExtras(container)
+    }
+    val viewModel: CartViewModel = viewModel(
+        factory = CartViewModel.Factory,
+        extras = extras,
+    )
+
+    val cartState by viewModel.cartUiState.collectAsState()
+
+    Scaffold(
+        topBar = {
+            CenterAlignedTopAppBar(
+                navigationIcon = {
+                    IconButton(onClick = onNavBack) {
+                        Icon(
+                            imageVector = Icons.AutoMirrored.Filled.ArrowBack,
+                            contentDescription = "Navigate back",
+                        )
+                    }
+                },
+                title = {
+                    Text(text = stringResource(R.string.frutties))
+                },
+                colors = TopAppBarColors(
+                    containerColor = MaterialTheme.colorScheme.primary,
+                    scrolledContainerColor = MaterialTheme.colorScheme.primary,
+                    navigationIconContentColor = MaterialTheme.colorScheme.onPrimary,
+                    titleContentColor = MaterialTheme.colorScheme.onPrimary,
+                    actionIconContentColor = MaterialTheme.colorScheme.onPrimary,
+                ),
+            )
+        },
+        contentWindowInsets = WindowInsets.safeDrawing.only(
+            // Do not include Bottom so scrolled content is drawn below system bars.
+            // Include Horizontal because some devices have camera cutouts on the side.
+            WindowInsetsSides.Top + WindowInsetsSides.Horizontal,
+        ),
+    ) { paddingValues ->
+        Column(
+            modifier = Modifier
+                .padding(16.dp)
+                // Support edge-to-edge (required on Android 15)
+                // https://developer.android.com/develop/ui/compose/layouts/insets#inset-size
+                .padding(paddingValues),
+        ) {
+            val cartItemCount = cartState.cartDetails.sumOf { it.count }
+            Text(
+                text = "Cart has $cartItemCount items",
+                modifier = Modifier.padding(8.dp),
+            )
+            LazyColumn(
+                modifier = Modifier.fillMaxWidth(),
+                horizontalAlignment = Alignment.CenterHorizontally,
+            ) {
+                items(cartState.cartDetails) { cartItem ->
+                    Text(text = "${cartItem.fruittie.name}: ${cartItem.count}")
+                }
+                item {
+                    Spacer(
+                        Modifier.windowInsetsBottomHeight(
+                            WindowInsets.systemBars,
+                        ),
+                    )
+                }
+            }
+        }
+    }
+}