SwiftUI Academy · 课时

声明 @State 属性

添加 @State 以保存视图本地的可变数据。

声明 @State 属性 是 CoddyKit 上的免费 SwiftUI 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 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。

Meet the @State Wrapper

You declare mutable view-local data by marking a property with @State. This property wrapper tells SwiftUI to store and watch the value for you. 🏷️

@State private var count = 0

Always Give It a Default

A @State property needs an initial value right where you declare it. SwiftUI uses it to create the storage the first time the view appears.

@State private var isOn = false

Mark It private

State belongs to one view, so declare it private. This signals that no outside code should reach in and set it directly, keeping ownership clear.

@State private var name = ""

Reading the Value

Read a @State property like any normal variable. Just use its name in body and SwiftUI tracks that this view depends on it.

Text("You tapped \(count) times")

Writing the Value

You can mutate a @State property even though the view is a struct. Assign to it from an action and SwiftUI schedules a redraw automatically.

Button("Add") { count += 1 }

It Persists Across Redraws

SwiftUI keeps the @State value alive across the many times the view body is recomputed. Your count won't reset just because the view redrew.

Putting It Together

Declare state, read it in the body, and mutate it from a button. That is the full loop that powers most simple interactions.

struct CounterView: View {
    @State private var count = 0
    var body: some View {
        Button("Count \(count)") { count += 1 }
    }
}

Use Simple Value Types

@State works best with value types like Int, Bool, String, or small structs. For shared objects you'll later reach for other tools, but values are the norm here.

One Owner Per Property

The view that declares @State is its owner. Other views can receive access, but only one view should hold the original state for a given value.

Don't Overuse It

Reach for @State only when a value truly changes while the view is on screen. Constant labels and passed-in data don't need it.

Naming for Clarity

Name state for what it represents, like isLoading or selectedTab. Clear names make the data flow obvious to anyone reading the view.

Quick Check

Which line correctly declares a private piece of view-local state?

Recap

Declare changing view data with @State, give it a default, and keep it private. Read it freely in body and mutate it from actions to trigger redraws. ✅

常见问题解答

「声明 @State 属性」课时是免费的吗？

是的 — 「声明 @State 属性」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。

「声明 @State 属性」这节课中我会学到什么？

添加 @State 以保存视图本地的可变数据。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 2 节课，共 4 节。

「声明 @State 属性」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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