Demonstrate KMP ViewModel on multiple screens #71

cartland · 2025-06-23T22:50:20Z

This introduces Jetpack Navigation 3 on Android and NavigationStack on iOS.

Android:

Updates compileSdk and targetSdk to 36 in androidApp build.gradle.kts.
Adds kotlinx-serialization plugin.
Implements basic navigation using Navigation3 for the ListScreen and CartScreen.
Adds CartScreen composable.
Integrates CartViewModel and AppContainer for dependency injection in CartScreen.
Updates dependencies in libs.versions.toml, including Navigation3 and kotlinx-serialization.

iOS:

Adds ObservableViewModel for SwiftUI interop.
Updates iosApp to use NavigationStack and integrate cart navigation.
Adds CartViewModelStoreOwner for ios.

This commit introduces Navigation3 for screen navigation and updates several dependencies: Android: - Updates compileSdk and targetSdk to 36 in androidApp build.gradle.kts. - Adds kotlinx-serialization plugin. - Implements basic navigation using Navigation3 for the ListScreen and CartScreen. - Adds CartScreen composable. - Integrates CartViewModel and AppContainer for dependency injection in CartScreen. - Updates dependencies in libs.versions.toml, including Navigation3 and kotlinx-serialization. iOS: - Adds ObservableViewModel for swiftui interop. - Updates iosApp to use NavigationStack and integrate cart navigation. - Adds CartViewModelStoreOwner for ios.

This commit refactors the CartScreen in both Android and iOS and removes the ObservableViewModel in iOS. Android: - Updates padding on CartScreen for better layout. - Centers items horizontally within the LazyColumn. iOS: - Removes ObservableViewModel.swift as it is no longer needed. - Clears mainViewModelStoreOwner on ContentView disappear.

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Summary of Changes

Hello @cartland, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the application's architecture by introducing multi-screen navigation capabilities on both Android and iOS platforms. It demonstrates how to effectively use Kotlin Multiplatform (KMP) ViewModels to manage UI state across different screens, leveraging platform-specific navigation frameworks while maintaining a shared business logic layer. The changes also involve necessary SDK and dependency updates for modern Android and iOS development.

Highlights

Multi-Platform Navigation Integration: Implemented distinct navigation solutions for Android (Jetpack Navigation 3) and iOS (SwiftUI NavigationStack) to support multi-screen flows within the application.
Dedicated Cart ViewModel: Introduced a new CartViewModel to manage cart-specific UI state and logic, separating it from the MainViewModel for better modularity and adherence to KMP ViewModel patterns.
KMP ViewModel Demonstration: Showcased the effective use of Kotlin Multiplatform (KMP) ViewModels (MainViewModel and CartViewModel) across different screens on both Android and iOS, demonstrating shared logic with platform-specific UI.
Android SDK & Dependency Updates: Upgraded Android compileSdk and targetSdk to 36 and integrated new Navigation3 and kotlinx-serialization dependencies to support modern Android development practices.
iOS Deployment Target Update: Increased the iOS deployment target to 16.6 to enable the use of SwiftUI's NavigationStack for improved navigation capabilities.

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Code Review

This pull request introduces multi-screen navigation using Jetpack Navigation 3 on Android and NavigationStack on iOS, demonstrating a shared ViewModel architecture in a KMP project. The changes are well-structured, separating concerns into different ViewModels and screens. My review focuses on improving navigation consistency, dependency management risks with snapshot versions, API usage in Compose, and ensuring robust dependency injection and view logic in both Android and iOS implementations.

gemini-code-assist · 2025-06-23T22:53:57Z

Fruitties/gradle/libs.versions.toml

+nav3Core = "1.0.0-alpha01"
+lifecycleViewmodelNav3 = "1.0.0-alpha01"
+kotlinxSerializationCore = "1.8.1"
+material3AdaptiveNav3 = "1.0.0-SNAPSHOT"


The material3AdaptiveNav3 dependency is using a SNAPSHOT version. Snapshot dependencies are unstable, can change without notice, and may break your build at any time. They should be avoided, especially in production or release builds.

gemini-code-assist · 2025-06-23T22:53:57Z

Fruitties/settings.gradle.kts

+        maven {
+            url = uri("https://androidx.dev/snapshots/builds/13617490/artifacts/repository")
+        }


The snapshot repository URL is pinned to a specific build ID (13617490). This is very brittle. If that build artifact is removed from the server, your build will fail. It's generally better to use a generic snapshot URL (e.g., one that always points to the latest snapshot) if available.

gemini-code-assist · 2025-06-23T22:53:57Z

Fruitties/shared/src/commonMain/kotlin/com/example/fruitties/viewmodel/CartViewModel.kt

+            )
+
+    companion object {
+        val APP_CONTAINER_KEY = CreationExtras.Key<AppContainer>()


The APP_CONTAINER_KEY is also defined in MainViewModel. This creates two separate instances of CreationExtras.Key for the same purpose, which could lead to bugs. It's best to define this key once in a shared location and have both ViewModels reference that single instance.

gemini-code-assist · 2025-06-23T22:53:57Z

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

+                    onNavBack = {
+                        backStack.clear()
+                        backStack.add(ListScreenKey)
+                    },


The navigation logic for the back button in the CartScreen's top app bar is inconsistent with the system back behavior. Currently, it clears the entire back stack and navigates to a new ListScreen. This is more of a "navigate up to home" action. The system back gesture, handled by onBack in NavDisplay, will simply pop the CartScreen off the stack. For a consistent user experience, consider using the same pop behavior for the in-app back button.

onNavBack = { backStack.removeLastOrNull() },

gemini-code-assist · 2025-06-23T22:53:57Z

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

+                colors = TopAppBarColors(
+                    containerColor = MaterialTheme.colorScheme.primary,
+                    scrolledContainerColor = MaterialTheme.colorScheme.primary,
+                    navigationIconContentColor = MaterialTheme.colorScheme.onPrimary,
+                    titleContentColor = MaterialTheme.colorScheme.onPrimary,
+                    actionIconContentColor = MaterialTheme.colorScheme.onPrimary,
+                ),


Instead of manually constructing TopAppBarColors, it's recommended to use the default factory function from TopAppBarDefaults. This ensures that the colors are consistent with the MaterialTheme and handles different states (like disabled) correctly, making your UI more robust and easier to maintain.

colors = TopAppBarDefaults.centerAlignedTopAppBarColors( containerColor = MaterialTheme.colorScheme.primary, navigationIconContentColor = MaterialTheme.colorScheme.onPrimary, titleContentColor = MaterialTheme.colorScheme.onPrimary, actionIconContentColor = MaterialTheme.colorScheme.onPrimary, ),

gemini-code-assist · 2025-06-23T22:53:57Z

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

+        ) {
+            val cartItemCount = cartState.cartDetails.sumOf { it.count }
+            Text(
+                text = "Cart has $cartItemCount items",


The text is hardcoded. For better maintainability and to support internationalization (i18n), it's best practice to use string resources.

text = stringResource(R.string.cart_summary, cartItemCount),

gemini-code-assist · 2025-06-23T22:53:57Z

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

-            LazyColumn {
+            LazyColumn(
+                modifier = Modifier.fillMaxWidth(),
+                verticalArrangement = Arrangement.spacedBy(64.dp),


A vertical arrangement spacing of 64.dp between items in the LazyColumn is quite large and might not be what you intended. If this is a typo, you might want to adjust it to a more common value like 8.dp or 16.dp.

Suggested change

verticalArrangement = Arrangement.spacedBy(64.dp),

verticalArrangement = Arrangement.spacedBy(16.dp),

gemini-code-assist · 2025-06-23T22:53:58Z

Fruitties/iosApp/iosApp/ContentView.swift

+                Observing(mainViewModel.homeUiState) { homeUIState in
+                    ScrollView {
+                        LazyVStack {
+                            ForEach(homeUIState.fruitties, id: \.self) { value in


Using id: \.self for ForEach requires Fruittie to be Hashable. While this might work if Fruittie is a class and you have unique instances, it's safer and more explicit to use a stable, unique identifier from the data model, like an id property. The Android ListScreen uses key = { it.id }, which suggests a stable id is available.

Suggested change

ForEach(homeUIState.fruitties, id: \.self) { value in

ForEach(homeUIState.fruitties, id: \.id) { value in

gemini-code-assist · 2025-06-23T22:53:58Z

...ties/shared/src/iosMain/kotlin/com/example/fruitties/di/viewmodel/CartViewModelStoreOwner.kt

+    // Create an instance of CartViewModel with the CreationExtras.
+    val cartViewModel: CartViewModel by lazy {
+        ViewModelProvider.create(
+            owner = this as ViewModelStoreOwner,


The cast this as ViewModelStoreOwner is redundant because the class CartViewModelStoreOwner already implements the ViewModelStoreOwner interface. You can safely remove it for cleaner code.

Suggested change

owner = this as ViewModelStoreOwner,

owner = this,

cartland added 2 commits June 23, 2025 13:19

gemini-code-assist bot reviewed Jun 23, 2025

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cartland closed this Jun 24, 2025

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Demonstrate KMP ViewModel on multiple screens #71

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	verticalArrangement = Arrangement.spacedBy(64.dp),
	verticalArrangement = Arrangement.spacedBy(16.dp),

	ForEach(homeUIState.fruitties, id: \.self) { value in
	ForEach(homeUIState.fruitties, id: \.id) { value in

Demonstrate KMP ViewModel on multiple screens #71

Demonstrate KMP ViewModel on multiple screens #71

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cartland commented Jun 23, 2025

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