Building a document-based app with SwiftUI

At a glance

Project structure

Source bundle/
├── WritingApp/
│   ├── WritingApp.swift
│   ├── Views/
│   │   ├── AccessoryView.swift
│   │   ├── StoryView.swift
│   │   └── StorySheet.swift
│   ├── WritingAppDocument.swift
│   ├── Extensions/
│   │   ├── UTType+WritingApp.swift
│   │   └── Color.swift
│   ├── Info.plist
│   └── WritingApp.entitlements
├── Configuration/
│   └── SampleCode.xcconfig
└── WritingApp.xcodeproj/
    ├── .xcodesamplecode.plist
    └── project.pbxproj

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 6 source declaration(s).

Overall architecture

flowchart LR
    N1["WritingApp"]
    N2["AccessoryView"]
    N3["WritingAppDocument"]
    N4["SwiftUI APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4

Reference code

WritingApp/WritingApp.swift:11 — architecture anchor

@main
struct WritingApp: App {
    var body: some Scene {
        #if os(iOS)
        DocumentGroupLaunchScene("Writing App") {
            NewDocumentButton("Start Writing")
        } background: {
            Image(.pinkJungle)
                .resizable()
                .scaledToFill()
                .ignoresSafeArea()
        } overlayAccessoryView: { _ in
            AccessoryView()
        }
        #endif
        DocumentGroup(newDocument: WritingAppDocument()) { file in
            StoryView(document: file.$document)
        }
    }
}

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
    AccessoryView *-- CGSize : size
    StoryView o-- WritingAppDocument : document
    StoryView *-- Bool : isFocused
    WritingAppDocument *-- String : story

Ownership evidence

WritingApp/Views/AccessoryView.swift:12 — stored dependency or nearest verified ownership anchor

struct AccessoryView: View {
    // ...
    @State private var size: CGSize = CGSize()
    // ...
}

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.

No source-visible execution, scheduling, or synchronization boundary was found in the indexed source.

@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.

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

WritingApp/WritingApp.swift:12 — representative type boundary

@main
struct WritingApp: App {
    // ...
            NewDocumentButton("Start Writing")
    // ...
}

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

Access control

Reference code

WritingApp/Views/AccessoryView.swift:11 — representative boundary

struct AccessoryView: View {
    @Environment(\.horizontalSizeClass) private var horizontal
    // ...
}

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: WritingApp; Document: WritingAppDocument; View: AccessoryView, StoryView.
• Protocols: no local protocol declaration in the scanned source.
• Methods: fileWrapper.
• Files: WritingApp/WritingApp.swift, WritingApp/Views/AccessoryView.swift, WritingApp/Views/StoryView.swift, WritingApp/WritingAppDocument.swift, WritingApp/Views/StorySheet.swift.

Architecture takeaways

• WritingApp is the main source-visible entry or composition anchor for this sample.
• Framework work reaches SwiftUI, UniformTypeIdentifiers 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