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Kotlin 协程与 ViewModel 的完美结合

web 2025/6/19 23:09:29

在 Android 开发中，Kotlin 协程与 ViewModel 的结合是现代应用架构的核心。这种组合提供了高效、简洁的异步处理解决方案，同时保持代码的清晰和可维护性。

核心优势

生命周期感知：协程在 ViewModel 作用域内自动取消，避免内存泄漏
简化异步代码：用同步方式编写异步逻辑
错误处理：统一异常处理机制
线程管理：轻松切换线程上下文

基础实现

1. 添加依赖

dependencies {// ViewModel 和协程支持implementation "androidx.lifecycle:lifecycle-viewmodel-ktx:2.6.2"implementation "androidx.lifecycle:lifecycle-runtime-ktx:2.6.2"implementation "org.jetbrains.kotlinx:kotlinx-coroutines-android:1.7.3"
}

2. 创建协程支持的 ViewModel

class UserViewModel : ViewModel() {private val _users = MutableStateFlow<List<User>>(emptyList())val users: StateFlow<List<User>> = _usersprivate val _loading = MutableStateFlow(false)val loading: StateFlow<Boolean> = _loadingprivate val _error = MutableSharedFlow<String>()val error: SharedFlow<String> = _error// 使用 viewModelScope 启动协程fun loadUsers() {viewModelScope.launch {try {_loading.value = trueval result = userRepository.getUsers() // 挂起函数_users.value = result} catch (e: Exception) {_error.emit("加载失败: ${e.message}")} finally {_loading.value = false}}}
}

进阶用法

1. 结合 Flow 使用

class DataViewModel : ViewModel() {private val _searchQuery = MutableStateFlow("")val searchResults: StateFlow<List<Item>> = _searchQuery.debounce(300) // 防抖处理.distinctUntilChanged().filter { it.length > 2 }.flatMapLatest { query ->flow {emit(emptyList()) // 显示加载状态emit(repository.searchItems(query))}}.stateIn(scope = viewModelScope,started = SharingStarted.WhileSubscribed(5000),initialValue = emptyList())fun search(query: String) {_searchQuery.value = query}
}

2. 并行处理

fun loadUserDetails(userId: String) {viewModelScope.launch {_loading.value = true// 并行执行多个请求val userDeferred = async { userRepo.getUser(userId) }val postsDeferred = async { postRepo.getPosts(userId) }val friendsDeferred = async { friendRepo.getFriends(userId) }try {val user = userDeferred.await()val posts = postsDeferred.await()val friends = friendsDeferred.await()_userDetails.value = UserDetails(user, posts, friends)} catch (e: Exception) {_error.emit("加载详情失败")} finally {_loading.value = false}}
}

3. 超时处理

kotlin

fun fetchDataWithTimeout() {viewModelScope.launch {try {val result = withTimeout(10_000) { // 10秒超时apiService.fetchData()}_data.value = result} catch (e: TimeoutCancellationException) {_error.emit("请求超时")}}
}

最佳实践

1. 分离业务逻辑

// UserViewModel.kt
class UserViewModel(private val userRepo: UserRepository) : ViewModel() {private val _users = MutableStateFlow<List<User>>(emptyList())val users: StateFlow<List<User>> = _usersfun loadUsers() {viewModelScope.launch {_users.value = userRepo.getUsers()}}
}// UserRepository.kt
class UserRepository(private val api: UserApi) {suspend fun getUsers(): List<User> {return api.getUsers().mapToDomain()}
}

2. 错误处理封装

// 扩展函数简化错误处理
fun <T> ViewModel.launchWithErrorHandling(onError: (Throwable) -> Unit = { _ -> },block: suspend () -> T
) {viewModelScope.launch {try {block()} catch (e: Exception) {onError(e)}}
}// 使用示例
fun loadData() {launchWithErrorHandling(onError = { e -> _error.emit("Error: ${e.message}") }) {_data.value = repository.fetchData()}
}

3. 测试策略

@OptIn(ExperimentalCoroutinesApi::class)
class UserViewModelTest {@get:Ruleval rule = InstantTaskExecutorRule()private lateinit var viewModel: UserViewModelprivate val testDispatcher = StandardTestDispatcher()@Beforefun setup() {Dispatchers.setMain(testDispatcher)viewModel = UserViewModel(FakeUserRepository())}@Afterfun tearDown() {Dispatchers.resetMain()}@Testfun `loadUsers should update state`() = runTest {viewModel.loadUsers()testDispatcher.scheduler.advanceUntilIdle()assertEquals(3, viewModel.users.value.size)}
}

常见问题解决

1. 协程取消问题

fun startLongRunningTask() {viewModelScope.launch {// 定期检查协程是否活跃for (i in 1..100) {ensureActive() // 如果协程被取消则抛出异常// 或者手动检查if (!isActive) return@launch// 执行任务delay(1000)}}
}

2. 冷流与热流选择

场景	推荐选择	说明
一次性数据	StateFlow	简单状态管理
事件处理	SharedFlow	避免事件丢失
复杂数据流	Flow	冷流，按需执行
响应式UI	StateFlow/Flow	结合Lifecycle

3. 生命周期处理

class MainActivity : AppCompatActivity() {override fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)lifecycleScope.launch {// 当Activity在后台时暂停收集repeatOnLifecycle(Lifecycle.State.STARTED) {viewModel.users.collect { users ->updateUI(users)}}}}
}

性能优化技巧

使用缓冲：

val events = MutableSharedFlow<Event>(extraBufferCapacity = 64,onBufferOverflow = BufferOverflow.DROP_OLDEST
)

避免重复启动协程：

private var searchJob: Job? = nullfun search(query: String) {searchJob?.cancel()searchJob = viewModelScope.launch {// 执行搜索}
}

使用协程调度器优化：

viewModelScope.launch(Dispatchers.Default) {// CPU密集型操作
}viewModelScope.launch(Dispatchers.IO) {// IO操作
}viewModelScope.launch(Dispatchers.Main.immediate) {// UI更新
}