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ViewModel 中的 suspend 调用

在主线程之外获取数据。

ViewModel 中的 suspend 调用 是 CoddyKit 上的免费 Jetpack Compose Academy 课时。这是第 3 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。

Never Block the Main Thread

Network calls take time, and doing them on the UI thread freezes your app. You move that work off the main thread instead.

Make the Endpoint suspend

Mark your Retrofit function with the suspend keyword. Now it returns the parsed result directly and can pause without blocking. ⏸️

@GET("users")
suspend fun getUsers(): List<User>

The ViewModel Owns the Logic

Fetching data belongs in the ViewModel, not the Composable. It survives rotation and keeps your UI code purely about display.

class UserViewModel : ViewModel() {
    // network logic lives here
}

Launch With viewModelScope

A suspend function needs a coroutine. viewModelScope gives you one that is cancelled automatically when the ViewModel clears.

viewModelScope.launch {
    val users = api.getUsers()
}

Store the Result in State

Once the call returns, save the data into a state property so Compose can observe it and redraw the screen.

var users by mutableStateOf<List<User>>(emptyList())

Wrap It In a try-catch

Networks fail, so guard the call with try-catch. An unhandled exception in a coroutine can crash your whole app.

try {
    users = api.getUsers()
} catch (e: Exception) {
    // handle failure
}

Fetch on Init

Trigger the first load in the ViewModel's init block, so data starts arriving the moment the screen is created.

init {
    loadUsers()
}

Keep It in a Function

Wrap the fetch in a named function like loadUsers. That makes it easy to call again for retry or pull-to-refresh.

fun loadUsers() = viewModelScope.launch {
    users = api.getUsers()
}

Dispatchers Handle Threading

Retrofit already runs the request on a background dispatcher, so you usually don't switch threads with Dispatchers.IO yourself.

Collect State in Compose

In your Composable, read the ViewModel's state. Because it's observable, Compose recomposes the instant fresh data lands.

val users = viewModel.users

Cancellation Is Automatic

If the user leaves and the ViewModel clears, viewModelScope cancels the in-flight call, so you waste no work on a dead screen.

Quick Check

Which scope cancels its coroutines automatically when the ViewModel is cleared?

Recap: Calling From the ViewModel

You made endpoints suspend, launched them in viewModelScope, stored results in state, and caught errors. Next you'll render loading, success, and error states.

常见问题解答

「ViewModel 中的 suspend 调用」课时是免费的吗？

是的 — 「ViewModel 中的 suspend 调用」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。

「ViewModel 中的 suspend 调用」这节课中我会学到什么？

在主线程之外获取数据。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 3 节课，共 4 节。

「ViewModel 中的 suspend 调用」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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