Bringing multiple windows to your SwiftUI app

At a glance

Project structure

Source bundle/
└── BookClub/
    ├── BookClubApp.swift
    ├── Views/
    │   ├── CircularProgressView.swift
    │   ├── LinearProgressView.swift
    │   ├── StackedProgressView.swift
    │   ├── BookDetail/
    │   │   └── BookDetailHeader.swift
    │   └── BookCover.swift
    └── Models/
        ├── NavigationModel.swift
        ├── ProgressEditorModel.swift
        ├── ReadingListModel.swift
        ├── CurrentlyReading.swift
        ├── ReadingProgress.swift
        └── ReadingActivityItem.swift

Structure observations

• Architecturally prominent files are ranked from entry points and role-named declarations; resource-only paths are omitted.
• Primary languages: Swift.
• The verified tree contains 5 project/configuration file(s) and 51 source declaration(s).

Overall architecture

flowchart LR
    N1["BookClubApp"]
    N2["ArcView"]
    N3["NavigationModel"]
    N4["SeededRandomNumberGenerator"]
    N5["SwiftUI APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4
    N4 --> N5

Reference code

BookClub/BookClubApp.swift:11 — architecture anchor

@main
struct BookClubApp: App {
    private var dataModel = ReadingListModel()

    var body: some Scene {
        WindowGroup("Reading List") {
            ReadingList(model: dataModel)
        }
        .commands {
            SidebarCommands()
        }
        #if os(macOS)
        WindowGroup("Book Details", for: Book.ID.self) { $bookId in
            BookDetailWindow(dataModel: dataModel, bookId: $bookId)
        }
        .commandsRemoved()

        Window("Reading Activity", id: "activity") {
            ReadingActivityList(activity: dataModel.activity)
                .frame(minWidth: 640, minHeight: 480)
        }
        .keyboardShortcut("1")
        .defaultPosition(.topTrailing)
        .defaultSize(width: 800, height: 600)
        #endif
    }
}

Interpretation

The arrows summarize the source-visible entry, role-named types or folders, and framework direction; when nodes come from structural folders, the sequence is a high-level interpretation rather than proof that every adjacent node calls the next. Ownership is claimed only where the next section cites a stored property or assignment. The diagram is intentionally limited to the dominant path into SwiftUI.

Ownership and state

classDiagram
    BookClubApp *-- ReadingListModel : dataModel
    NavigationModel o-- NavigationSplitViewVisibility : columnVisibility
    NavigationModel o-- Category : selectedCategory
    NavigationModel *-- Set : selectedBookIds

Ownership evidence

BookClub/BookClubApp.swift:13 — stored dependency or nearest verified ownership anchor

@main
struct BookClubApp: App {
    private var dataModel = ReadingListModel()
    // ...
}

Composition arrows indicate a source-visible construction expression or locally owned value state; aggregation means the owner stores or receives a dependency without proving exclusive lifetime ownership.

Concurrency, scheduling, and thread safety

Evidence limit: actor isolation, async/await, or Task creation does not by itself prove background-thread execution; Sendable conformance alone does not prove thread-safe mutation.

@MainActor/MainActor.run, DispatchQueue.main, and RunLoop.main are reported as distinct isolation, queue, and event-loop mechanisms. A plain Task is kept separate from Task.detached; neither is labeled as a background thread.

Reference code

BookClub/Views/ReadingList.swift:43 — representative execution boundary

            for await jsonData in navigationModel.$jsonData.values {
                if let data = jsonData {
                    navigationData = data
                }
            }

State propagation, frameworks, and dependencies

Evidence limit: an import proves a source-level compilation dependency at the cited line; it does not prove runtime use, architectural adoption, or whether a Swift package is a direct application dependency.

receive(on:) describes downstream delivery scheduling, while subscribe(on:) describes upstream subscription/request/cancel scheduling. An import Combine alone establishes neither behavior nor a Store, reducer, Redux, or other application architecture.

Class and protocol design

BookClub/BookClubApp.swift:12 — representative type boundary

@main
struct BookClubApp: App {
    private var dataModel = ReadingListModel()
    // ...
}

No local protocol conformance is claimed as protocol-oriented design; external framework conformances are listed only as dependencies.

Access control

Reference code

BookClub/BookClubApp.swift:13 — representative boundary

@main
struct BookClubApp: App {
    private var dataModel = ReadingListModel()
    // ...
}

Swift declarations without a modifier are internal; explicit private, fileprivate, private(set), public, or open entries above are interpreted by language semantics. Objective-C/C samples instead rely on header and implementation boundaries, which are not equivalent to Swift lexical privacy.

Logic ownership and placement

Design patterns

Naming conventions

• Types: App: BookClubApp; Factory: MockFactory; Generator: SeededRandomNumberGenerator; Model: NavigationModel, ProgressEditorModel, ReadingListModel; View: ArcView, CircularProgressView, LinearReadingProgressView, StackedProgressView.
• Protocols: no local protocol declaration in the scanned source.
• Methods: makeBody, path, inset, encode, present, dismiss, togglePresentation, foregroundStyle.
• Files: BookClub/BookClubApp.swift, BookClub/Views/CircularProgressView.swift, BookClub/Models/NavigationModel.swift, BookClub/Models/ProgressEditorModel.swift, BookClub/Views/StackedProgressView.swift, BookClub/Models/ReadingListModel.swift.

Architecture takeaways

• BookClubApp is the main source-visible entry or composition anchor for this sample.
• Framework work reaches SwiftUI, Charts through a deliberately small high-level chain; the detailed API graph remains inside the cited implementation files.
• Stored-property evidence identifies lifecycle collaboration; it does not by itself prove exclusive object ownership.
• Access-control conclusions separate verified language visibility from the likely design rationale.
• The source does not justify labeling the design protocol-oriented.

Source map

• Official Apple documentation