Kotlin流操作符简介

1. 启动操作符

1.1. collect启动流并处理值

lifecycleScope.launch {    flow.collect { value ->         // 处理值    }}

1.2. launchIn在指定作用域中异步启动流

flow.onEach { updateUI(it) }    .launchIn(viewModelScope)

2. 共享操作符

2.1. stateIn转换为状态流

flow.stateIn(    scope = viewModelScope,    started = SharingStarted.WhileSubscribed(5000), // 5秒保活    initialValue = null)

2.2. shareIn转换为共享流

flow.shareIn(    scope = coroutineScope,    started = SharingStarted.WhileSubscribed,    replay = 1 // 新订阅者接收最近1个值)

3. 单次取值操作符

3.1. first取首个值

val result = flow.first() // 对空流抛出NoSuchElementException

3.2. firstOrNull取首个值或null

val result = flow.firstOrNull() // 对空流安全

3.3. toList/toSet 收集全部值并转换为集合

4. 聚合操作符

4.1. fold带初始值的累积计算

val sum = flow.fold(0) { acc, value -> acc + value }

4.2. reduce无初始值累积

val sum = flowOf(1, 2, 3, 4).reduce { accumulator, value ->    accumulator + value // 累积求和 (结果为10)}

5. 转换与组合操作符

5.1. transform转换值

flowOf(1, 2).transform { emit(it * 2); emit(it + 1) } // 输出：2, 3, 4, 5

5.2. flatMapMerge合并、转换并展平

flowOf(1, 2).flatMapMerge { flowOf(it, it * 2) }

5.3. flatMapLatest转换并展平最新流（取消前序未完成转换）

flowOf(1, 2).flatMapLatest { flowOf(it, it * 2) }

5.4. combine合并多个流的最新值

flow1.combine(flow2) { a, b -> "a-b" }

6. 时间处理操作符

6.1. debounce防抖

flow { emit(1); delay(100); emit(2) }.debounce(200) 

6.2. sample定时采样最新值

flow { while(true) emit("弹幕") }.sample(1000)

7. 错误处理与资源管理

7.1. retryWhen条件重试

.retryWhen { cause, attempt -> attempt < 3 && cause is IOException }

7.2. cancellable响应协程取消

flow { ... }.cancellable()

8. Android扩展

8.1. flowWithLifecycle绑定生命周期的流

// implementation("androidx.lifecycle:lifecycle-runtime-ktx:2.6.0")

flow.flowWithLifecycle(lifecycle, Lifecycle.State.STARTED)
    .collect { ... }

8.2. repeatOnLifecycle根据生命周期自动取消或重启协程

lifecycleScope.launch {    repeatOnLifecycle(Lifecycle.State.STARTED) {        viewModel.uiState.collect { ... }    }}