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GeometryReader 基础

测量可用空间，为内容确定尺寸。

GeometryReader 基础 是 CoddyKit 上的免费 SwiftUI 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 SwiftUI Academy 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 SwiftUI 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。

Measuring Space

Sometimes a view needs to know how big its slot is. GeometryReader hands you the exact size and position of the space it occupies. 📐

It Is a Container

A GeometryReader is a view whose body is a closure receiving a proxy that describes the available space.

GeometryReader { proxy in
    Text("Hi")
}

The Proxy

That closure parameter is a GeometryProxy. It carries the size, safe-area insets, and frame of the reader.

GeometryReader { proxy in
    let w = proxy.size.width
    Color.blue.frame(width: w)
}

Reading the Size

The most common move is proxy.size, a CGSize giving you the width and height you can fill.

GeometryReader { proxy in
    Text("\(proxy.size.width)")
}

Half the Width

Use the measured width for proportional sizing, like making a bar exactly half of the available width.

GeometryReader { proxy in
    Color.green
        .frame(width: proxy.size.width / 2)
}

It Fills by Default

A GeometryReader greedily takes all the space its parent offers, so its children align to the top-left unless you center them.

Centering Content

Because content pins top-left, wrap it or add a frame with alignment to center children inside the reader.

GeometryReader { proxy in
    Text("Center")
        .frame(width: proxy.size.width,
               height: proxy.size.height)
}

Global Coordinates

Ask for a view position in the window with proxy.frame(in: .global), handy for scroll effects and overlays.

let f = proxy.frame(in: .global)
Text("\(f.minY)")

Safe Area Insets

The proxy also exposes safeAreaInsets, so you can respect notches and home indicators in custom layouts.

let top = proxy.safeAreaInsets.top

Use It Sparingly

A GeometryReader changes layout behavior, so reach for it only when you truly need measurements, not as a default wrapper. ⚠️

Scroll-Driven Effects

Combined with a ScrollView, reading each item frame lets you build parallax and fade effects tied to scroll position.

Quick Check

Recall what the closure hands you.

Recap

You can now read available space with GeometryReader, size views proportionally, and read frames for scroll-aware effects. 🎉

常见问题解答

「GeometryReader 基础」课时是免费的吗？

是的 — 「GeometryReader 基础」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 SwiftUI Academy 课程的其余内容，请升级到 CoddyKit PRO。 SwiftUI Academy 课程共包含 4 节课。

「GeometryReader 基础」这节课中我会学到什么？

测量可用空间，为内容确定尺寸。你通过在浏览器中直接运行的动手代码来练习 SwiftUI 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 SwiftUI Academy 需要有经验吗？

无需任何先前经验。CoddyKit 上的 SwiftUI 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。

「GeometryReader 基础」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 SwiftUI Academy 课中编写并运行代码吗？

能。每节 SwiftUI 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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