Controlling a DockKit accessory using your camera app

At a glance

Project structure

Source bundle/
└── DockKitCamera/
    ├── DockKit_CameraApp.swift
    ├── Model/
    │   ├── DataTypes.swift
    │   ├── CameraModel.swift
    │   ├── DockAccessoryController.swift
    │   └── DockControllerModel.swift
    ├── Preview Content/
    │   ├── PreviewCameraModel.swift
    │   └── PreviewDockAccessoryControllerModel.swift
    ├── Views/
    │   ├── CameraPreview.swift
    │   └── BatteryView.swift
    ├── CaptureService.swift
    ├── ContentView.swift
    └── DockControlService.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 4 project/configuration file(s) and 58 source declaration(s).

Overall architecture

flowchart LR
    N1["DockKit_CameraApp"]
    N2["ContentView"]
    N3["CameraModel"]
    N4["CaptureService"]
    N5["DockKit APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4
    N4 --> N5

Reference code

DockKitCamera/DockKit_CameraApp.swift:11 — architecture anchor

@main
struct DockKitCameraApp: App {

    @State private var camera = CameraModel()

    @State private var dockController = DockControllerModel()

    var body: some Scene {
        WindowGroup {
            ContentView(camera: camera, dockController: dockController)
                .task {
                    await camera.setTrackingServiceDelegate(dockController)
                    await dockController.setCameraCaptureServiceDelegate(camera)
                    // Start the capture pipeline.
                    await camera.start()
                }
        }
    }
}

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 DockKit.

Ownership and state

classDiagram
    DockKitCameraApp *-- CameraModel : camera
    DockKitCameraApp *-- DockControllerModel : dockController
    DockKitCameraApp *-- Logger : logger
    Movie *-- URL : url

Ownership evidence

DockKitCamera/DockKit_CameraApp.swift:14 — stored dependency or nearest verified ownership anchor

@main
struct DockKitCameraApp: App {
    // ...
    @State private var camera = CameraModel()
    // ...
}

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

DockKitCamera/Camera/MovieCapture.swift:63 — representative execution boundary

final class MovieCapture: NSObject, OutputService {
    // ...
        metadataOutput.setMetadataObjectsDelegate(self, queue: DispatchQueue(label: "MetaDataOutputQueue"))
    // ...
}

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

DockKitCamera/Model/DataTypes.swift:113 — representative type boundary

protocol OutputService {
    associatedtype Output: AVCaptureOutput
    var output: Output { get }
    var captureActivity: CaptureActivity { get }
    func updateConfiguration(for device: AVCaptureDevice)
    func setVideoRotationAngle(_ angle: CGFloat)
}

The source explicitly defines local protocol relationships: MovieCapture → OutputService, CameraModel → Camera, DockControllerModel → DockController, PreviewCameraModel → Camera, PreviewSourceStub → PreviewSource, PreviewDockControllerModel → DockController.

Access control

Reference code

DockKitCamera/Camera/DeviceLookup.swift:15 — representative boundary

final class DeviceLookup {
    // ...
    private let frontCameraDiscoverySession: AVCaptureDevice.DiscoverySession
    // ...
}

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

Main application flow

sequenceDiagram
    participant DockControlService
    participant DockAccessoryManager
    participant dockkitAccessory
    participant Task
    DockControlService->>DockAccessoryManager: setSystemTrackingEnabled()
    DockControlService->>dockkitAccessory: animate()
    DockControlService->>Task: sleep()
    DockControlService->>DockAccessoryManager: setSystemTrackingEnabled()
    DockControlService->>DockAccessoryManager: setSystemTrackingEnabled()

Reference code

DockKitCamera/DockControlService.swift:260 — animate()

    func animate(_ animation: Animation) async -> Bool {
// ...
#if !targetEnvironment(simulator)
        guard let dockkitAccessory = dockkitAccessory else {
            logger.error("No DockKit accessory connected")
            return false
        }
        if animating {
            logger.error("DockKit accessory busy animating")
            return false
        }
        do {
            animating = true
            try await DockAccessoryManager.shared.setSystemTrackingEnabled(false)
            let progress = try await dockkitAccessory.animate(motion: dockKitAnimation(from: animation))
            while !progress.isCancelled && !progress.isFinished {
                try await Task.sleep(nanoseconds: NSEC_PER_SEC / 10) // 0.1 sec
            }
            try await DockAccessoryManager.shared.setSystemTrackingEnabled(trackingMode == .system ? true : false)
        } catch {
            logger.error("Error executing animation \(animation.rawValue) : \(error)")
            try? await DockAccessoryManager.shared.setSystemTrackingEnabled(trackingMode == .system ? true : false)
            animating = false
            return false
        }
        animating = false
#endif
        return true
    }

Naming conventions

• Types: App: DockKitCameraApp; Controller: DockController; Delegate: CameraCaptureDelegate, DockAccessoryTrackingDelegate, MovieCaptureDelegate; Model: CameraModel, DockControllerModel, PreviewCameraModel, PreviewDockControllerModel; Service: CaptureService, DockControlService, OutputService; View: BatteryView, ChevronView, ConnectionView, ContentView, PreviewView.
• Protocols: OutputService, DockAccessoryTrackingDelegate, CameraCaptureDelegate, DockController, PreviewSource, PreviewTarget, Camera.
• Methods: updateConfiguration, setVideoRotationAngle, getVideoRotationAngle, update, track, startOrStartCapture, switchCamera, zoom.
• Files: DockKitCamera/Preview Content/PreviewCameraModel.swift, DockKitCamera/Views/CameraPreview.swift, DockKitCamera/CaptureService.swift, DockKitCamera/ContentView.swift, DockKitCamera/DockControlService.swift, DockKitCamera/Model/CameraModel.swift.

Architecture takeaways

• DockKit_CameraApp is the main source-visible entry or composition anchor for this sample.
• Framework work reaches SwiftUI, AVFoundation, UIKit, DockKit 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