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SwiftUI 如何重新计算视图

理解标识、值和差异计算。

SwiftUI 如何重新计算视图 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。

Views Are Cheap Descriptions

A SwiftUI view is not a heavy object. It is a lightweight description of what the screen should look like right now. SwiftUI builds and discards them constantly.

body Runs Again and Again

When data changes, SwiftUI calls your view's body again to get a fresh description. This is normal and expected, not a bug.

var body: some View {
    Text("Count: \(count)")
}

Diffing the Two Trees

SwiftUI compares the new description against the old one. This diffing step finds the small set of things that actually changed.

Only Changes Reach the Screen

After diffing, only the parts that truly differ are redrawn. Everything else stays exactly as it was, which keeps updates fast.

Value Identity

For most views, SwiftUI compares them by value. If a struct's stored properties are unchanged, SwiftUI can skip work for that view.

Structural Identity

SwiftUI also tracks a view's structural identity: its position in the view tree. Same slot means same view across updates.

Explicit Identity with id

You can give a view an explicit id. A changed id tells SwiftUI to treat it as a brand new view, resetting its state.

ProfileView()
    .id(selectedUser.id)

Identity in ForEach

In a list, stable identity lets SwiftUI move rows instead of rebuilding them. Use a real id, not the array index.

ForEach(items) { item in
    RowView(item: item)
}

Dependencies Drive Updates

A view re-evaluates only when a value it actually reads changes. These reads are its dependencies, and they define when body runs.

Recompute Is Not Redraw

Running body is cheap; touching the GPU is not. A recompute often produces an identical result, so nothing is actually redrawn.

Why This Mental Model Matters

Knowing how SwiftUI diffs means you optimize the right thing: stable identity and minimal dependencies, not avoiding body calls entirely.

Quick Check

What does SwiftUI do after rebuilding a view's body?

Recap: How Views Recompute

You saw that SwiftUI rebuilds body, diffs the result, and redraws only real changes. Identity and dependencies decide when that happens. 🧠

常见问题解答

「SwiftUI 如何重新计算视图」课时是免费的吗？

是的 — 「SwiftUI 如何重新计算视图」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。

「SwiftUI 如何重新计算视图」这节课中我会学到什么？

理解标识、值和差异计算。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。

「SwiftUI 如何重新计算视图」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。

此课程中的所有课时

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