Creating screen annotations for objects in an AR experience

At a glance

Project structure

Source bundle/
└── ScreenSpace-Sample/
    ├── AppDelegate.swift
    └── ViewController/
        ├── Components/
        │   └── ScreenSpaceComponent.swift
        ├── ViewController.swift
        ├── Views/
        │   ├── GradientView.swift
        │   ├── StickyNoteView.swift
        │   └── MessageLabel.swift
        ├── Delegates/
        │   ├── ViewController+ARCoachingOverlayDelegate.swift
        │   └── ViewController+UITextViewDelegate.swift
        ├── Entities/
        │   └── StickyNoteEntity.swift
        ├── Gestures/
        │   └── ViewController+Gestures.swift
        └── Utilities/
            ├── Keyboard+Helpers.swift
            └── SIMD+Helpers.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 6 project/configuration file(s) and 9 source declaration(s).

Overall architecture

flowchart LR
    N1["AppDelegate"]
    N2["ViewController"]
    N3["ARKit APIs"]
    N1 --> N2
    N2 --> N3

Reference code

ScreenSpace-Sample/AppDelegate.swift:10 — architecture anchor

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]? = nil) -> Bool {
        guard ARWorldTrackingConfiguration.isSupported else {
            fatalError("""
                ARKit is not available on this device. For apps that require ARKit
                for core functionality, use the `arkit` key in the key in the
                `UIRequiredDeviceCapabilities` section of the Info.plist to prevent
                the app from installing. (If the app can't be installed, this error
                can't be triggered in a production scenario.)
                In apps where AR is an additive feature, use `isSupported` to
                determine whether to show UI for launching AR experiences.
            """) // For details, see https://developer.apple.com/documentation/arkit
        }

        return true
    }

}

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 ARKit.

Ownership and state

classDiagram
    AppDelegate o-- UIWindow : window
    ScreenSpaceComponent o-- StickyNoteView : view
    ScreenSpaceComponent o-- Projection : projection
    Projection *-- CGPoint : projectedPoint

Ownership evidence

ScreenSpace-Sample/AppDelegate.swift:13 — stored dependency or nearest verified ownership anchor

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
    // ...
    var window: UIWindow?
    // ...
}

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

ScreenSpace-Sample/ViewController/ViewController.swift:101 — representative execution boundary

        DispatchQueue.main.async {
            // ...
            let alertController = UIAlertController(title: "The AR session failed.", message: errorMessage, preferredStyle: .alert)
            // ...
        }

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

ScreenSpace-Sample/ViewController/Components/ScreenSpaceComponent.swift:11 — representative type boundary

protocol HasScreenSpaceView: Entity {
    var screenSpaceComponent: ScreenSpaceComponent { get set }
}

The source explicitly defines local protocol relationships: StickyNoteEntity → HasScreenSpaceView.

Access control

Reference code

ScreenSpace-Sample/ViewController/Delegates/ViewController+UITextViewDelegate.swift:56 — representative boundary

    fileprivate func clearPlaceholderText(_ stickyView: StickyNoteView, _ textView: UITextView) {
        // ...
            textView.text = ""
            textView.textColor = .white
        // ...
    }

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: Component: ScreenSpaceComponent; Controller: ViewController; Delegate: AppDelegate; View: GradientView, HasScreenSpaceView, StickyNoteView.
• Protocols: HasScreenSpaceView.
• Methods: application, getCenterPoint, setPositionCenter, animateTo, updateScreenPosition, viewDidLoad, viewWillAppear, viewDidAppear.
• Files: ScreenSpace-Sample/AppDelegate.swift, ScreenSpace-Sample/ViewController/Components/ScreenSpaceComponent.swift, ScreenSpace-Sample/ViewController/ViewController.swift, ScreenSpace-Sample/ViewController/Views/GradientView.swift, ScreenSpace-Sample/ViewController/Views/StickyNoteView.swift, ScreenSpace-Sample/ViewController/Entities/StickyNoteEntity.swift.

Architecture takeaways

• AppDelegate is the main source-visible entry or composition anchor for this sample.
• Framework work reaches UIKit, ARKit, RealityKit 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.
• Local protocol relationships provide an explicit substitution boundary.

Source map

• Official Apple documentation