映射与组合 Flow
在数据流到达屏幕前转换它们。
映射与组合 Flow 是 CoddyKit 上的免费 Jetpack Compose Academy 课时。 这是第 2 节课，共 4 节。 你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。 这是 Jetpack Compose Academy 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 Jetpack Compose Academy 课程共包含 4 节课。
本课时的部分内容尚未翻译，以英文显示。
Shape Data Before the UI
Raw data rarely matches what the screen needs. You use flow operators to transform a stream into ready-to-render UI state.
Transform with map
The map operator runs a function on each emission and passes the result downstream, leaving the original stream untouched.
val names = users.map { it.name }Filter Out Noise
Use filter to drop emissions you do not care about, so only the items that pass your condition reach the UI.
val active = users.filter { it.isActive }Combine Two Streams
The combine operator merges multiple flows and re-runs whenever any of them emits, giving you the latest value from each.
combine(query, results) { q, r -> SearchUi(q, r) }Combine Builds UI State
A common pattern is to combine several source flows into one immutable UiState object that fully describes the screen.
combine(items, loading, error) { i, l, e ->
UiState(i, l, e)
}Wait for All with zip
While combine fires on any change, zip pairs emissions one-to-one and waits until both flows have produced a new value.
flowA.zip(flowB) { a, b -> a + b }Switch to a New Stream
With flatMapLatest a new value cancels the previous inner flow and switches to a fresh one, perfect for live search.
query.flatMapLatest { repo.search(it) }Operators Are Cold by Default
Transformations like map and filter are cold: they describe work but do nothing until something downstream collects.
Chain Operators Freely
You can chain operators into a pipeline. Each one reads the stream above it and feeds the one below, top to bottom.
users.filter { it.isActive }
.map { it.name }Handle Errors in the Chain
The catch operator intercepts exceptions upstream so you can emit a fallback instead of crashing the whole stream.
repo.load().catch { emit(emptyList()) }Keep Logic in the ViewModel
Do your combine and map work in the ViewModel, then expose one clean state flow. The Composable stays simple and dumb.
Quick Check
Pick the operator for the job.
Recap: Mapping & Combining
Great work! Operators like map, filter, and combine reshape and merge streams in the ViewModel so the UI gets exactly the state it needs. 🎯
常见问题解答
「映射与组合 Flow」课时是免费的吗？
是的 — 「映射与组合 Flow」的完整文本可在网页上免费阅读。要进行交互式练习（内置代码编辑器和全天候 AI 导师）并解锁 Jetpack Compose Academy 课程的其余内容，请升级到 CoddyKit PRO。 Jetpack Compose Academy 课程共包含 4 节课。
「映射与组合 Flow」这节课中我会学到什么？
在数据流到达屏幕前转换它们。 你通过在浏览器中直接运行的动手代码来练习 Jetpack Compose Academy，全天候 AI 导师会在你学习这节课的过程中回答你的问题。
学习 Jetpack Compose Academy 需要有经验吗？
无需任何先前经验。CoddyKit 上的 Jetpack Compose Academy 课程适合初学者到高级学习者，你可以从这里开始或从头开始，按照自己的节奏学习。 这是第 2 节课，共 4 节。
「映射与组合 Flow」课时需要多长时间？
大多数 CoddyKit 课程大约需要 5–10 分钟。每节课都很精短且互动，所以你能稳步进步，并在网页和应用中从离开的地方继续。
我能在这节 Jetpack Compose Academy 课中编写并运行代码吗？
能。每节 Jetpack Compose Academy 课都包含内置代码编辑器，你可以在浏览器中直接编写并运行真实代码，并获得即时 AI 反馈 — 无需本地设置。