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Swift Academy · Lesson

@State: Local Mutable State in Views

Using @State to drive UI updates from private view state.

@State: Local Mutable State in Views is a free Swift Academy lesson on CoddyKit — lesson 2 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Swift Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Welcome

`@State` is the simplest SwiftUI state management tool. It stores a mutable value inside a view and triggers a re-render whenever it changes.

@State Basics

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

Private by Convention

Mark `@State` properties `private` — they are implementation details of the view, not part of its interface.

State Storage

SwiftUI manages the backing storage for `@State` separately from the struct. Even though the view struct is recreated on each render, the state value persists.

@State with Strings

```swift struct NameInput: View { @State private var name = "" var body: some View { TextField("Enter name", text: $name) Text("Hello, \(name)!") } } ```

@State with Booleans

```swift struct ToggleDemo: View { @State private var isOn = false var body: some View { Toggle("Enable", isOn: $isOn) if isOn { Text("Enabled!") } } } ```

Triggering Re-renders

Any mutation to `@State` causes SwiftUI to call `body` again. SwiftUI's render engine efficiently diffs the result and only updates changed parts of the UI.

@State for Complex Values

```swift struct Item: Identifiable { let id = UUID(); var text: String } struct ListView: View { @State private var items: [Item] = [] ... } ```

Limitations of @State

• Local only — not shareable across views without `@Binding` • Best for primitive types and small structs • For shared or complex state, use `@StateObject` / `@ObservableObject`

@State vs @StateObject

• `@State` — value type, owned by view, use for primitives • `@StateObject` — reference type, owned by view, use for ObservableObject models

Quick Check

What triggers a view re-render when using `@State`?

Recap

Key takeaways: • `@State` stores local mutable state owned by the view • Mark `private` — implementation detail • Mutations → automatic re-render • SwiftUI persists state across body re-evaluations • Use `@Binding` to share state with child views Next: View Modifiers.

Frequently asked questions

Is the “@State: Local Mutable State in Views” lesson free?

Yes — the full text of “@State: Local Mutable State in Views” is free to read here on the web, and the Swift Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Swift Academy course, upgrade to CoddyKit PRO.

What will I learn in “@State: Local Mutable State in Views”?

Using @State to drive UI updates from private view state. You practise Swift Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Swift Academy?

No prior experience is required. Swift Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 2 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “@State: Local Mutable State in Views” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Swift Academy lesson?

Yes. Every Swift Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

  1. The View Protocol and Body Property
  2. @State: Local Mutable State in Views
  3. View Modifiers: Chaining and Custom Modifiers
  4. Previews and the Preview Provider
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