Split app to 2 screens with Navigation3 and NavigationStack #73
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This commit introduces the following changes: **Android App:** - Implemented basic navigation between `ListScreen` and a new `CartScreen` using Navigation 3. - `ListScreen` now displays a "View Cart" button showing the item count. - `CartScreen` is a new Composable that displays the items in the cart. **iOS App:** - Updated `ContentView` to include a navigation link to `CartView`. - The "View Cart" link on `ContentView` now displays the cart item count. - `CartView` now directly observes `cartViewModel.cartUiState`. - Removed the expand/collapse functionality from `CartView` and made `CartDetailsView` always visible within a `ScrollView`. **Shared Code:** - Introduced a new `CartViewModel` to manage the state of the shopping cart, separating concerns from `MainViewModel`. - `MainViewModel`'s `HomeUiState` now includes `cartItemCount`. The previous `cartUiState` and its direct cart details have been removed from `MainViewModel`. - Renamed `IOSViewModelOwner` to `IOSViewModelStoreOwner` and updated its methods to provide `MainViewModel` and `CartViewModel`. - Updated Android compile SDK to 36. - Added Kotlinx Serialization plugin. **Dependency Updates:** - Added `androidx.navigation3` and `kotlinx-serialization-core` dependencies.
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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 on both Android and iOS platforms. It achieves this by separating the cart's business logic into a dedicated ViewModel in the shared module, leading to cleaner code and improved maintainability. The UI has been adapted on both platforms to support these new navigation flows and display relevant cart information.
Highlights
- Multi-Screen Navigation Implementation: Introduced multi-screen navigation for both Android and iOS applications. Android now uses Navigation3 to navigate between a
ListScreenand a newCartScreen, while iOS utilizesNavigationStackto linkContentViewto a newCartView. - Cart Logic Separation and ViewModel Refactoring: Extracted cart-specific state management and logic into a new
CartViewModelwithin the shared Kotlin Multiplatform module. This refactorsMainViewModelto focus solely on the main list functionality, withHomeUiStatenow including only thecartItemCount. - Platform-Specific UI Adjustments: Updated Android's
ListScreento remove direct cart display and integrate with the new navigation flow, simplifyingFruittieItemUI. On iOS,CartViewwas refactored to directly observe the newCartViewModeland its cart details are now always visible within aScrollView, removing previous expand/collapse functionality. - Dependency and SDK Updates: Upgraded the Android compile SDK to 36 across both the Android app and shared modules. Added necessary
androidx.navigation3andkotlinx-serialization-coredependencies, and updated iOS deployment target to 16.6.
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Code Review
This pull request splits the UI into two screens, ListScreen/ContentView and CartScreen/CartView, for Android and iOS respectively, and introduces CartViewModel to separate concerns. The use of Navigation3 and NavigationStack is a welcome improvement.
Suggestions include refining the navigation logic, improving UI performance by reducing redundant observers, and enhancing maintainability by centralizing state calculations in the ViewModel.
| entry<CartScreenKey> { | ||
| CartScreen( | ||
| onNavBarBack = { | ||
| backStack.removeIf { it is CartScreenKey } |
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Using removeIf here will remove all CartScreenKey entries from the back stack. To simply go back to the previous screen, use removeLastOrNull() instead.
| backStack.removeIf { it is CartScreenKey } | |
| backStack.removeLastOrNull() |
| @@ -110,34 +97,33 @@ fun ListScreen() { | |||
| ) { paddingValues -> | |||
| Column( | |||
| modifier = Modifier | |||
| .padding(horizontal = 16.dp) | |||
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The padding(horizontal = 16.dp) is redundant because start = 16.dp and end = 16.dp are set in the subsequent padding modifier. Remove the first padding call.
modifier = Modifier
// Support edge-to-edge (required on Android 15)
// https://developer.android.com/develop/ui/compose/layouts/insets#inset-size
.padding(
// Draw to bottom edge. LazyColumn adds a Spacer for WindowInsets.systemBars.
// No bottom padding.
top = paddingValues.calculateTopPadding(),
start = 16.dp,
end = 16.dp,
)| Observing(mainViewModel.homeUiState) { homeUIState in | ||
| ScrollView { | ||
| LazyVStack { | ||
| ForEach(homeUIState.fruitties, id: \.self) { value in | ||
| FruittieView(fruittie: value, addToCart: { fruittie in | ||
| Task { | ||
| mainViewModel.addItemToCart(fruittie: fruittie) | ||
| } | ||
| }) | ||
| } | ||
| }) | ||
| } | ||
| } | ||
| } |
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There are two Observing calls on the same mainViewModel.homeUiState. This creates two subscriptions to the same flow. Use a single Observing block that wraps the views that depend on the state.
NavigationStack {
VStack {
Text("Fruitties").font(.largeTitle).fontWeight(.bold)
Observing(mainViewModel.homeUiState) { homeUIState in
NavigationLink {
CartView(cartViewModel: cartViewModel)
} label: {
let total = homeUIState.cartItemCount
Text("View Cart (\(total))")
}
ScrollView {
LazyVStack {
ForEach(homeUIState.fruitties, id: \.self) { value in
FruittieView(fruittie: value, addToCart: { fruittie in
Task {
mainViewModel.addItemToCart(fruittie: fruittie)
}
})
}
}
}
}
}
}| val cartUiState: StateFlow<CartUiState> = | ||
| repository.cartDetails | ||
| .map { CartUiState(it) } | ||
| .stateIn( | ||
| scope = viewModelScope, | ||
| started = SharingStarted.WhileSubscribed(TIMEOUT_MILLIS), | ||
| initialValue = CartUiState(), | ||
| ) |
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Calculate the total item count here and store it in the CartUiState to avoid duplicate calculations in both Android and iOS UI code.
You'll also need to update CartUiState (at lines 67-69) to include the totalItemCount property:
data class CartUiState(
val cartDetails: List<CartItemDetails> = listOf(),
val totalItemCount: Int = 0,
) val cartUiState: StateFlow<CartUiState> =
repository.cartDetails
.map { details ->
CartUiState(
cartDetails = details,
totalItemCount = details.sumOf { it.count }
)
}
.stateIn(
scope = viewModelScope,
started = SharingStarted.WhileSubscribed(TIMEOUT_MILLIS),
initialValue = CartUiState(),
)This commit refactors the calculation of the total number of items in the cart. Previously, the total item count was calculated independently in both the Android `CartScreen.kt` and iOS `CartView.swift`. This change moves the calculation into the shared `CartViewModel.kt`. A new `totalItemCount` property is added to `CartUiState`, which is now populated within the `map` function that transforms the `repository.cartDetails` flow. This centralization simplifies the UI components and ensures consistency in how the total item count is determined across platforms.
This commit introduces the following changes:
Android App:
ListScreenand a newCartScreenusing Navigation 3.ListScreennow displays a "View Cart" button showing the item count.CartScreenis a new Composable that displays the items in the cart.iOS App:
ContentViewto include a navigation link toCartView.ContentViewnow displays the cart item count.CartViewnow directly observescartViewModel.cartUiState.CartViewand madeCartDetailsViewalways visible within aScrollView.Shared Code:
CartViewModelto manage the state of the shopping cart, separating concerns fromMainViewModel.MainViewModel'sHomeUiStatenow includescartItemCount. The previouscartUiStateand its direct cart details have been removed fromMainViewModel.IOSViewModelOwnertoIOSViewModelStoreOwnerand updated its methods to provideMainViewModelandCartViewModel.Dependency Updates:
androidx.navigation3andkotlinx-serialization-coredependencies.