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Kotlin + Compose Flow State 手册

news 2026/7/31 14:30:21

概念	作用	示例
MutableStateFlow / StateFlow	状态流，UI 绑定	上面的 Counter 示例
MutableSharedFlow / SharedFlow	事件流，多收集者	上面的 EventLogger 示例
asStateFlow / asSharedFlow	封装可变流	上面封装状态/事件流示例
collectAsState / collectAsStateWithLifecycle	Flow → Compose State	StatusScreen 示例
asFlow	集合/数组 → Flow	NumberList 示例
remember	Compose 内临时状态	RememberExample
rememberSaveable	跨配置状态保存	RememberSaveableExample
rememberCoroutineScope	Compose 内协程	CoroutineExample

名称	类型	定义 / 作用	是否可变	用途 / 场景	示例
`MutableStateFlow<T>`	Flow	可变状态流，保存单个状态值	可变	ViewModel 内部状态，状态驱动 UI	`_uiState = MutableStateFlow(0)`
`StateFlow<T>`	Flow	对 MutableStateFlow 的只读封装	只读	向 UI 暴露状态	`val uiState: StateFlow<Int> = _uiState.asStateFlow()`
`MutableSharedFlow<T>`	Flow	可变事件流，发射事件，可被多个收集者收集，可设置 replay	可变	事件总线、网络事件、日志、一次性事件	`_events = MutableSharedFlow<TcpEvent>()`
`SharedFlow<T>`	Flow	对 MutableSharedFlow 的只读封装	只读	向 UI/外部暴露事件	`val events: SharedFlow<TcpEvent> = _events.asSharedFlow()`
`asStateFlow()`	方法	将 MutableStateFlow 包装成只读 StateFlow	N/A	封装内部状态，保证只读	`_uiState.asStateFlow()`
`asSharedFlow()`	方法	将 MutableSharedFlow 包装成只读 SharedFlow	N/A	封装事件流，保证只读	`_events.asSharedFlow()`
`collectAsState(initial = ...)`	Compose 扩展	将 Flow/StateFlow 收集并转成 Compose State，UI 可直接观察	N/A	Compose 页面直接订阅状态流	`val uiState by viewModel.uiState.collectAsState()`
`collectAsStateWithLifecycle(initial = ...)`	Compose 扩展	和`collectAsState`类似，但会自动结合 Lifecycle，暂停/恢复收集	N/A	避免页面后台也收集，节省资源	`val uiState by viewModel.uiState.collectAsStateWithLifecycle()`
`asFlow()`	方法	将集合、数组、Channel 转换为 Flow	N/A	快速把已有数据转为 Flow	`listOf(1,2,3).asFlow()`
`remember { }`	Compose	保存 UI 内部状态，重组时不丢失	N/A	文本框内容、开关状态	`val count = remember { mutableStateOf(0) }`
`rememberSaveable { }`	Compose	可序列化状态保存，重组或配置变化后恢复	N/A	表单输入、滚动位置	`val scroll = rememberSaveable { mutableStateOf(0) }`
`rememberCoroutineScope()`	Compose	提供与 Composable 生命周期绑定的 CoroutineScope	N/A	在 Composable 内启动协程	`val scope = rememberCoroutineScope()`

1. MutableStateFlow / StateFlow

作用: 保存状态，UI 可响应式绑定

// ViewModel private val _count = MutableStateFlow(0) val count: StateFlow<Int> = _count.asStateFlow() fun increment() { _count.value += 1 } // Compose 页面 @Composable fun Counter(viewModel: MyViewModel) { val count by viewModel.count.collectAsState() Column { Text("Count: $count") Button(onClick = { viewModel.increment() }) { Text("Increment") } } }

2. MutableSharedFlow / SharedFlow

作用: 事件流，多收集者都能收到

// ViewModel private val _events = MutableSharedFlow<String>() val events: SharedFlow<String> = _events.asSharedFlow() fun triggerEvent(msg: String) { viewModelScope.launch { _events.emit(msg) } } // Compose 页面 @Composable fun EventLogger(viewModel: MyViewModel) { val scope = rememberCoroutineScope() LaunchedEffect(Unit) { viewModel.events.collect { msg -> println("Received event: $msg") } } Button(onClick = { scope.launch { viewModel.triggerEvent("Hello") } }) { Text("Send Event") } }

3. asStateFlow / asSharedFlow

作用: 封装可变流，外部只读

private val _state = MutableStateFlow("Idle") val state: StateFlow<String> = _state.asStateFlow() private val _events = MutableSharedFlow<Int>() val events: SharedFlow<Int> = _events.asSharedFlow()

4. collectAsState / collectAsStateWithLifecycle

作用: Flow → Compose State，UI 自动刷新

@Composable fun StatusScreen(viewModel: MyViewModel) { val status by viewModel.state.collectAsState(initial = "Idle") Text("Status: $status") } @Composable fun StatusScreenSafe(viewModel: MyViewModel) { val status by viewModel.state.collectAsStateWithLifecycle(initial = "Idle") Text("Status: $status") }

5. asFlow()

作用: 集合 / 数组 / Channel → Flow

val numbers = listOf(1,2,3) val numberFlow = numbers.asFlow() @Composable fun NumberList() { LaunchedEffect(Unit) { numberFlow.collect { println(it) } // 输出 1 2 3 } }

6. remember

作用: 保存 Composable 内部状态，重组不丢失

@Composable fun RememberExample() { val count = remember { mutableStateOf(0) } Column { Text("Count: ${count.value}") Button(onClick = { count.value += 1 }) { Text("Increment") } } }

7. rememberSaveable

作用: 可跨配置变化（旋转屏幕）保存状态

@Composable fun RememberSaveableExample() { val text = rememberSaveable { mutableStateOf("") } TextField( value = text.value, onValueChange = { text.value = it }, label = { Text("Enter text") } ) }

8. rememberCoroutineScope()

作用: 提供 Compose 生命周期绑定的 CoroutineScope

@Composable fun CoroutineExample(viewModel: MyViewModel) { val scope = rememberCoroutineScope() Button(onClick = { scope.launch { viewModel.fetchData() // 启动协程调用网络或数据库 } }) { Text("Fetch") } }