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用于协程的 LaunchedEffect

启动与组合绑定的挂起任务。

用于协程的 LaunchedEffect 是 CoddyKit 上的免费 Jetpack Compose Academy 课时。这是第 1 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。

Effects Live Outside Composition

Composables should be pure and run many times. When you need to do real work like a network call, you reach for a side effect handler instead.

Meet LaunchedEffect

A LaunchedEffect runs suspend code in a coroutine that is tied to where it sits in your composition. Perfect for one-shot startup work. 🚀

It Starts When It Enters

When a LaunchedEffect first enters the composition, it launches its block. When it leaves the composition, the coroutine is cancelled for you.

LaunchedEffect(Unit) {
    loadProfile()
}

The Key Controls Restarts

The first argument is a key. If the key changes between recompositions, the old coroutine is cancelled and a fresh one starts.

LaunchedEffect(userId) {
    user = fetchUser(userId)
}

Use Unit to Run Once

Passing Unit (or true) as the key means the effect never restarts. It runs a single time when the Composable appears.

LaunchedEffect(Unit) {
    analytics.logScreenView()
}

Suspend Calls Are Welcome

Inside the block you can freely call suspend functions like delay or a Retrofit request. The coroutine scope is provided for you.

LaunchedEffect(Unit) {
    delay(2000)
    showSplash = false
}

Never Launch in the Body

Calling a coroutine directly in the Composable body is a bug. The body re-runs on every recomposition, so you would fire the work again and again.

Cancellation Is Automatic

When the user navigates away and the Composable leaves the screen, Compose cancels the coroutine. No manual cleanup, no leaks.

Pair It with State

Effects usually write their result into state so the UI redraws. Store the loaded data, and recomposition shows it.

var data by remember { mutableStateOf<List<Item>>(emptyList()) }
LaunchedEffect(Unit) { data = repo.load() }

Multiple Keys for Combined Triggers

You can pass several keys. The effect restarts whenever any of them changes, which is handy for re-fetching on filter changes.

LaunchedEffect(query, sort) {
    results = search(query, sort)
}

A Typical Loading Pattern

Together it reads like a recipe: set loading true, await the result, then store it. Compose handles the lifecycle around your coroutine.

LaunchedEffect(id) {
    loading = true
    item = repo.get(id)
    loading = false
}

Quick Check

Think about how restarts are controlled.

Recap: LaunchedEffect

Nice work! LaunchedEffect runs suspend code tied to composition, restarts when its key changes, and cancels itself automatically when the Composable leaves. 🎯

常见问题解答

「用于协程的 LaunchedEffect」课时是免费的吗？

是的 — 「用于协程的 LaunchedEffect」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。

「用于协程的 LaunchedEffect」这节课中我会学到什么？

启动与组合绑定的挂起任务。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 1 节课，共 4 节。

「用于协程的 LaunchedEffect」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。

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