swift-macos

What this skill does

# macOS App Development - Swift 6.2

Build native macOS apps with Swift 6.2 (latest: 6.2.4, Feb 2026), SwiftUI, SwiftData, and macOS 26 Tahoe. Target macOS 14+ for SwiftData/@Observable, macOS 15+ for latest SwiftUI, macOS 26 for Liquid Glass and Foundation Models.

## Quick Start

```swift
import SwiftUI
import SwiftData

@Model
final class Project {
    var name: String
    var createdAt: Date
    @Relationship(deleteRule: .cascade) var tasks: [Task] = []

    init(name: String) {
        self.name = name
        self.createdAt = .now
    }
}

@Model
final class Task {
    var title: String
    var isComplete: Bool
    var project: Project?

    init(title: String) {
        self.title = title
        self.isComplete = false
    }
}

@main
struct MyApp: App {
    var body: some Scene {
        WindowGroup("Projects") {
            ContentView()
        }
        .modelContainer(for: [Project.self, Task.self])
        .defaultSize(width: 900, height: 600)

        #if os(macOS)
        Settings { SettingsView() }

        MenuBarExtra("Status", systemImage: "circle.fill") {
            MenuBarView()
        }
        .menuBarExtraStyle(.window)
        #endif
    }
}

struct ContentView: View {
    @Query(sort: \Project.createdAt, order: .reverse)
    private var projects: [Project]

    @Environment(\.modelContext) private var context
    @State private var selected: Project?

    var body: some View {
        NavigationSplitView {
            List(projects, selection: $selected) { project in
                NavigationLink(value: project) {
                    Text(project.name)
                }
            }
            .navigationSplitViewColumnWidth(min: 200, ideal: 250)
        } detail: {
            if let selected {
                DetailView(project: selected)
            } else {
                ContentUnavailableView("Select a Project",
                    systemImage: "sidebar.left")
            }
        }
    }
}
```

## Scenes & Windows

| Scene | Purpose |
|-------|---------|
| `WindowGroup` | Resizable windows (multiple instances) |
| `Window` | Single-instance utility window |
| `Settings` | Preferences (Cmd+,) |
| `MenuBarExtra` | Menu bar with `.menu` or `.window` style |
| `DocumentGroup` | Document-based apps |

Open windows: `@Environment(\.openWindow) var openWindow; openWindow(id: "about")`

For complete scene lifecycle, see `references/app-lifecycle.md`.

## Menus & Commands

```swift
.commands {
    CommandGroup(replacing: .newItem) {
        Button("New Project") { /* ... */ }
            .keyboardShortcut("n", modifiers: .command)
    }
    CommandMenu("Tools") {
        Button("Run Analysis") { /* ... */ }
            .keyboardShortcut("r", modifiers: [.command, .shift])
    }
}
```

## Table (macOS-native)

```swift
Table(items, selection: $selectedIDs, sortOrder: $sortOrder) {
    TableColumn("Name", value: \.name)
    TableColumn("Date") { Text($0.date, format: .dateTime) }
        .width(min: 100, ideal: 150)
}
.contextMenu(forSelectionType: Item.ID.self) { ids in
    Button("Delete", role: .destructive) { delete(ids) }
}
```

For forms, popovers, sheets, inspector, and macOS modifiers, see `references/swiftui-macos.md`.

## @Observable

```swift
@Observable
final class AppState {
    var projects: [Project] = []
    var isLoading = false

    func load() async throws {
        isLoading = true
        defer { isLoading = false }
        projects = try await ProjectService.fetchAll()
    }
}

// Use: @State var state = AppState()          (owner)
// Pass: .environment(state)                    (inject)
// Read: @Environment(AppState.self) var state  (child)
```

## SwiftData

### @Query & #Predicate

```swift
@Query(filter: #Predicate<Project> { !$0.isArchived }, sort: \Project.name)
private var active: [Project]

// Dynamic predicate
func search(_ term: String) -> Predicate<Project> {
    #Predicate { $0.name.localizedStandardContains(term) }
}

// FetchDescriptor (outside views)
var desc = FetchDescriptor<Project>(predicate: #Predicate { $0.isArchived })
desc.fetchLimit = 50
let results = try context.fetch(desc)
let count = try context.fetchCount(desc)
```

### Relationships

```swift
@Model final class Author {
    var name: String
    @Relationship(deleteRule: .cascade, inverse: \Book.author)
    var books: [Book] = []
}

@Model final class Book {
    var title: String
    var author: Author?
    @Relationship var tags: [Tag] = []  // many-to-many
}
```

Delete rules: `.cascade`, `.nullify` (default), `.deny`, `.noAction`.

### Schema Migration

```swift
enum SchemaV1: VersionedSchema { /* ... */ }
enum SchemaV2: VersionedSchema { /* ... */ }

enum MigrationPlan: SchemaMigrationPlan {
    static var schemas: [any VersionedSchema.Type] { [SchemaV1.self, SchemaV2.self] }
    static var stages: [MigrationStage] {
        [.lightweight(fromVersion: SchemaV1.self, toVersion: SchemaV2.self)]
    }
}

// Apply: .modelContainer(for: Model.self, migrationPlan: MigrationPlan.self)
```

### CloudKit Sync

Enable iCloud capability, then `.modelContainer(for: Model.self)` auto-syncs. Constraints: all properties need defaults/optional, no unique constraints, optional relationships.

For model attributes, background contexts, batch ops, undo/redo, and testing, see SwiftData references below.

## Concurrency (Swift 6.2)

### Default MainActor Isolation

Opt entire module into main actor - all code runs on main actor by default:

```swift
// Package.swift
.executableTarget(name: "MyApp", swiftSettings: [
    .defaultIsolation(MainActor.self),
])
```

Or Xcode: Build Settings > Swift Compiler > Default Isolation > MainActor.

### @concurrent

Mark functions for background execution:

```swift
@concurrent
func processFile(_ url: URL) async throws -> Data {
    let data = try Data(contentsOf: url)
    return try compress(data) // runs off main actor
}
// After await, automatically back on main actor
let result = try await processFile(fileURL)
```

Use for CPU-intensive work, I/O, anything not touching UI.

### Actors

```swift
actor DocumentStore {
    private var docs: [UUID: Document] = [:]
    func add(_ doc: Document) { docs[doc.id] = doc }
    func get(_ id: UUID) -> Document? { docs[id] }
    nonisolated let name: String
}
// Requires await: let doc = await store.get(id)
```

### Structured Concurrency

```swift
// Parallel with async let
func loadDashboard() async throws -> Dashboard {
    async let profile = fetchProfile()
    async let stats = fetchStats()
    return try await Dashboard(profile: profile, stats: stats)
}

// Dynamic with TaskGroup
func processImages(_ urls: [URL]) async throws -> [NSImage] {
    try await withThrowingTaskGroup(of: (Int, NSImage).self) { group in
        for (i, url) in urls.enumerated() {
            group.addTask { (i, try await loadImage(url)) }
        }
        var results = [(Int, NSImage)]()
        for try await r in group { results.append(r) }
        return results.sorted { $0.0 < $1.0 }.map(\.1)
    }
}
```

### Sendable

```swift
struct Point: Sendable { var x, y: Double }              // value types: implicit
final class Config: Sendable { let apiURL: URL }          // final + immutable
actor SharedState { var count = 0 }                       // mutable: use actors
// Enable strict mode: .swiftLanguageMode(.v6) in Package.swift
```

### AsyncSequence & Observations

```swift
// Stream @Observable changes (macOS 26+ / iOS 26+, SE-0475)
// Observations uses a closure init, not Observations(of:).
let progresses = Observations { manager.progress }
for await p in progresses { print(p) }

// Typed NotificationCenter (macOS 26+)
struct DocSaved: NotificationCenter.MainActorMessage {
    typealias Subject = Document
    static var name: Notification.Name { .init("DocSaved") }
    let id: UUID
}
NotificationCenter.default.post(DocSaved(id: document.id), subject: document)
let token = NotificationCenter.default.addObserver(of: document, for: DocSaved.self) { msg in
    refresh(msg.id