Jetpack Compose Academy · 课时

使用 @Preview 实时预览

无需重新构建整个应用即可迭代用户界面。

使用 @Preview 实时预览 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。

See UI Without Running

Rebuilding the whole app to check one button is slow. The @Preview annotation renders your Composable right inside Android Studio. ⚡

Add the Annotation

Put @Preview above a Composable that takes no required parameters. Android Studio then shows it in the design pane beside your code.

@Preview
@Composable
fun GreetingPreview() {
    Greeting("Compose")
}

Previews Need No Arguments

A previewed Composable must be callable with no arguments. That is why you usually make a small wrapper that supplies sample data.

Wrap Your Real Composable

Keep your real Composable parameterized, then write a tiny preview wrapper that calls it with fixed values for the design pane.

@Preview
@Composable
fun CardPreview() {
    ProfileCard(name = "Ada")
}

Name It With a Title

Add name to label the preview in the panel. Helpful when one file shows several previews at once.

@Preview(name = "Dark card")
@Composable
fun DarkPreview() { /* ... */ }

Show System Decorations

Set showSystemUi to true to render the status bar and full device frame, so you see the Composable in a realistic phone shell.

@Preview(showSystemUi = true)
@Composable
fun ScreenPreview() { /* ... */ }

Just the Background

If you only want a surface behind your UI, use showBackground instead. It adds a plain backdrop without the whole device chrome.

@Preview(showBackground = true)
@Composable
fun ItemPreview() { /* ... */ }

Many Previews at Once

Stack several @Preview annotations on one function to compare states side by side, like light and dark or small and large fonts.

Preview Different Sizes

Pass widthDp and heightDp to test how your Composable looks on narrow or wide screens without launching an emulator.

@Preview(widthDp = 320, heightDp = 200)
@Composable
fun NarrowPreview() { /* ... */ }

Interactive Preview

Click the interactive mode icon in the preview pane to tap and scroll your UI without a full app run. Great for quick checks.

Previews Stay Out of the App

Code under @Preview is for tooling only. It never ships in your released app, so add as many previews as you find useful.

Quick Check

A quick check on how previews work.

Recap

You can now iterate fast: add @Preview, supply sample data in a wrapper, and tune name, sizes, and backgrounds to see your UI instantly. 🎨

常见问题解答

「使用 @Preview 实时预览」课时是免费的吗？

是的 — 「使用 @Preview 实时预览」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。

「使用 @Preview 实时预览」这节课中我会学到什么？

无需重新构建整个应用即可迭代用户界面。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。

「使用 @Preview 实时预览」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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