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@Composable 函数的组成

阅读一个 Composable，找出它的特殊之处。

第 3 / 4 课13 个步骤

@Composable 函数的组成 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。

What Is a Composable?

A Composable is just a Kotlin function that describes a piece of UI. Call it, and Compose draws that UI on screen. It is the building block of everything. 🧱

The @Composable Annotation

The magic marker is @Composable above the function. It tells the Compose compiler this function can emit UI and may be recomposed when data changes.

@Composable
fun Greeting() {
    Text("Hello!")
}

Name It Like a UI Piece

By convention, Composable names use PascalCase nouns like Greeting or ProfileCard, not verbs. The name describes the thing on screen, not an action.

It Returns Unit

A Composable usually returns nothing (Unit). Instead of returning UI, it emits it by calling other Composables inside its body. The side effect is the drawing.

Built-In Composables

Compose ships ready-made Composables like Text, Button, Image, and Icon. You combine these to build your own, so you rarely start from a blank canvas.

@Composable
fun Welcome() {
    Text("Welcome to Compose")
}

Parameters Pass In Data

Composables take parameters just like any function. Pass data in, and the UI reflects it. This is how the same component shows different content.

@Composable
fun Greeting(name: String) {
    Text("Hello, " + name)
}

The Modifier Parameter

Most Composables accept a modifier to control size, padding, and layout. By convention it is the first optional parameter, ready for you to customize.

Composables Call Composables

A Composable can only be called from another Composable. This rule lets Compose track the tree of UI and recompose the right parts when state changes.

Keep Them Small

Aim for small, focused Composables that do one thing. Tiny pieces are easier to reuse, preview, and combine into bigger screens later on.

Prefer No Side Effects

A good Composable is predictable: same inputs, same UI. Avoid surprises like network calls in the body, since Compose may run it many times.

Compose Builds a Tree

As Composables call each other, they form a UI tree. Compose walks this tree to draw the screen and to update only the branches that changed.

Quick Check

Let's verify what marks a function as a UI builder.

在交互式课程中回答

Recap: The Composable

A Composable is a Kotlin function with @Composable that emits UI, takes parameters, accepts a modifier, and calls other Composables to build a tree.

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常见问题解答

「@Composable 函数的组成」课时是免费的吗？

是的 — 「@Composable 函数的组成」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。

「@Composable 函数的组成」这节课中我会学到什么？

阅读一个 Composable，找出它的特殊之处。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。

「@Composable 函数的组成」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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