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148 lines
3.6 KiB
Markdown
148 lines
3.6 KiB
Markdown
---
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paths:
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- "**/*.kt"
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- "**/*.kts"
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---
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# Kotlin 模式
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> 此文件扩展了 [common/patterns.md](../common/patterns.md) 的内容，增加了 Kotlin 和 Android/KMP 特定的内容。
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## 依赖注入
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首选构造函数注入。使用 Koin（KMP）或 Hilt（仅限 Android）：
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```kotlin
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// Koin — declare modules
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val dataModule = module {
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single<ItemRepository> { ItemRepositoryImpl(get(), get()) }
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factory { GetItemsUseCase(get()) }
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viewModelOf(::ItemListViewModel)
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}
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// Hilt — annotations
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@HiltViewModel
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class ItemListViewModel @Inject constructor(
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private val getItems: GetItemsUseCase
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) : ViewModel()
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```
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## ViewModel 模式
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单一状态对象、事件接收器、单向数据流：
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```kotlin
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data class ScreenState(
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val items: List<Item> = emptyList(),
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val isLoading: Boolean = false
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)
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class ScreenViewModel(private val useCase: GetItemsUseCase) : ViewModel() {
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private val _state = MutableStateFlow(ScreenState())
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val state = _state.asStateFlow()
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fun onEvent(event: ScreenEvent) {
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when (event) {
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is ScreenEvent.Load -> load()
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is ScreenEvent.Delete -> delete(event.id)
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}
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}
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}
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```
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## 仓库模式
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* `suspend` 函数返回 `Result<T>` 或自定义错误类型
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* 对于响应式流使用 `Flow`
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* 协调本地和远程数据源
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```kotlin
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interface ItemRepository {
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suspend fun getById(id: String): Result<Item>
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suspend fun getAll(): Result<List<Item>>
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fun observeAll(): Flow<List<Item>>
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}
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```
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## 用例模式
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单一职责，`operator fun invoke`：
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```kotlin
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class GetItemUseCase(private val repository: ItemRepository) {
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suspend operator fun invoke(id: String): Result<Item> {
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return repository.getById(id)
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}
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}
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class GetItemsUseCase(private val repository: ItemRepository) {
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suspend operator fun invoke(): Result<List<Item>> {
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return repository.getAll()
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}
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}
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```
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## expect/actual (KMP)
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用于平台特定的实现：
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```kotlin
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// commonMain
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expect fun platformName(): String
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expect class SecureStorage {
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fun save(key: String, value: String)
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fun get(key: String): String?
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}
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// androidMain
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actual fun platformName(): String = "Android"
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actual class SecureStorage {
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actual fun save(key: String, value: String) { /* EncryptedSharedPreferences */ }
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actual fun get(key: String): String? = null /* ... */
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}
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// iosMain
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actual fun platformName(): String = "iOS"
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actual class SecureStorage {
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actual fun save(key: String, value: String) { /* Keychain */ }
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actual fun get(key: String): String? = null /* ... */
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}
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```
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## 协程模式
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* 在 ViewModels 中使用 `viewModelScope`，对于结构化的子工作使用 `coroutineScope`
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* 对于来自冷流的 StateFlow 使用 `stateIn(viewModelScope, SharingStarted.WhileSubscribed(5_000), initialValue)`
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* 当子任务失败应独立处理时使用 `supervisorScope`
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## 使用 DSL 的构建器模式
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```kotlin
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class HttpClientConfig {
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var baseUrl: String = ""
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var timeout: Long = 30_000
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private val interceptors = mutableListOf<Interceptor>()
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fun interceptor(block: () -> Interceptor) {
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interceptors.add(block())
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}
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}
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fun httpClient(block: HttpClientConfig.() -> Unit): HttpClient {
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val config = HttpClientConfig().apply(block)
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return HttpClient(config)
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}
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// Usage
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val client = httpClient {
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baseUrl = "https://api.example.com"
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timeout = 15_000
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interceptor { AuthInterceptor(tokenProvider) }
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}
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```
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## 参考
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有关详细的协程模式，请参阅技能：`kotlin-coroutines-flows`。
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有关模块和分层模式，请参阅技能：`android-clean-architecture`。
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