✅ViewModel

主要功能：

• 从 Repository 获取数据
• 将数据转换为 UI 状态
• 管理数据流和生命周期

1. 数据管理

HomeScreenViewModel.kt:

class HomeViewModel(itemsRepository: ItemsRepository): ViewModel(){
    companion object {
        private const val TIMEOUT_MILLIS = 5_000L
    }
    val homeUiState: StateFlow<HomeUiState> = itemsRepository.getAllItemsStream().map { HomeUiState(it) }
        .stateIn(scope = viewModelScope,
            started = SharingStarted.WhileSubscribed(TIMEOUT_MILLIS),
            initialValue = HomeUiState()
        )
}

/**
 * itemsRepository.getAllItemsStream() - 获取商品数据流
 *.map { HomeUiState(it) } - 将数据转换为 UI 状态
 *.stateIn(...) - 转换为 StateFlow 供 UI 使用
 */
data class HomeUiState(val itemList: List<Item> = listOf())

2. 业务逻辑处理

ItemEntryViewModel.kt:

class ItemEntryViewModel(private val itemsRepository: ItemsRepository) : ViewModel() {
    var itemUiState by mutableStateOf(ItemUiState())
        private set
    fun updateUiState(itemDetails: ItemDetails) {
        itemUiState =
            ItemUiState(itemDetails = itemDetails, isEntryValid = validateInput(itemDetails))
    }
    // 处理用户输入验证
    private fun validateInput(uiState: ItemDetails): Boolean {
        return with(uiState) {
            name.isNotBlank() && price.isNotBlank() && quantity.isNotBlank()
        }
    }
    
    // 处理数据保存
    suspend fun saveItem() {
        if (validateInput()) {
            itemsRepository.insertItem(itemUiState.itemDetails.toItem())
        }
    }
}

data class ItemDetails(
    val id: Int = 0,
    val name: String = "",
    val price: String = "",
    val quantity: String = "",
)

✅ViewModelProvider

主要功能：
创建 ViewModel 实例
注入必要的依赖（如 Repository）
管理 ViewModel 的生命周期

AppViewModelProvider.kt:

object AppViewModelProvider {
    val Factory = viewModelFactory {
        // Initializer for ItemEntryViewModel
        initializer {
            ItemEntryViewModel(inventoryApplication().container.itemsRepository)
        }

        // Initializer for HomeViewModel
        initializer {
            HomeViewModel(inventoryApplication().container.itemsRepository)
        }
    }
}

fun CreationExtras.inventoryApplication(): InventoryApplication =
    (this[AndroidViewModelFactory.APPLICATION_KEY] as InventoryApplication)