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Box：分层与重叠

在控制对齐方式的同时堆叠内容。

Box：分层与重叠 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。

Stacking on Top

When children should overlap rather than line up, you use a Box. It layers content on the same spot. 🗂️

Your First Box

A Box draws its children in order, each one on top of the previous. Later children sit above earlier ones, like stacked cards.

Box {
    Image(painter, null)
    Text("Caption")
}

Z-Order Follows Source Order

The last child you write wins the top layer. So to put a label over a photo, place the Image first and the Text after it.

Box Sizes to Its Biggest Child

By default a Box wraps its largest child. The other children are positioned within that footprint instead of expanding it.

Aligning the Whole Box

The contentAlignment parameter sets a default spot for every child. Alignment.Center pulls them all to the middle of the Box.

Box(contentAlignment = Alignment.Center) {
    Text("Centered")
}

Aligning One Child

Inside a Box, each child can use the align modifier to override the default. This is how you pin one item to a corner.

Box {
    Text("Top end", Modifier.align(Alignment.TopEnd))
}

A Badge in the Corner

Overlap plus align gives you a classic badge: an avatar fills the Box while a small dot pins to the TopEnd corner.

Box {
    Avatar()
    Dot(Modifier.align(Alignment.TopEnd))
}

Text Over an Image

A common pattern is a caption over a photo. Put the Image first, then align Text to BottomStart so it reads over the image.

Box {
    Image(painter, null)
    Text("Sunset", Modifier.align(Alignment.BottomStart))
}

Filling and Backgrounds

Make a Box fill space with fillMaxSize, then add a background color. It becomes a handy layered container for a whole screen.

Box(Modifier.fillMaxSize().background(Color.Black)) {
    Text("Hi")
}

The Nine Alignment Spots

A Box offers nine alignment positions, from TopStart to BottomEnd, with Center in the middle. They cover every placement you need.

When to Reach for Box

Choose Box whenever pieces share the same area: overlays, badges, captions, or a spinner centered over content. It is your layering tool.

Quick Check

Let's confirm how a Box layers its children.

Recap: Box

You learned Box: it stacks children on the same spot in source order, sizes to its biggest child, and uses contentAlignment and align to place them.

常见问题解答

「Box：分层与重叠」课时是免费的吗？

是的 — 「Box：分层与重叠」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。

「Box：分层与重叠」这节课中我会学到什么？

在控制对齐方式的同时堆叠内容。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。

「Box：分层与重叠」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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