Supporting Continuity Camera in your macOS app

At a glance

Project structure

ContinuityCam/
├── ContinuityCamApp.swift
├── ContentView.swift
├── Camera.swift
├── DeviceObservers.swift
└── Views/
    ├── CameraPreview.swift
    ├── ConfigurationView.swift
    └── MaterialView.swift

Camera.swift includes its supporting Device and VideoFormat value types and format extension. The split is by UI, camera model, and observation concern rather than a deep layer hierarchy.

Overall architecture

flowchart LR
    App["ContinuityCamApp"] --> View["ContentView"]
    View --> Camera["Camera ObservableObject"]
    Camera --> Session["AVCaptureSession"]
    Camera --> Preferred["PreferredCameraObserver"]
    Camera --> Effects["VideoEffectsObserver"]
    Camera --> Preview["CameraPreview adapter"]
    Config["ConfigurationView"] --> Camera

Reference code

ContinuityCam/ContentView.swift:10 — the root view creates one camera model and supplies its preview/configuration projections (abridged).

struct ContentView: View {
    @StateObject var camera = Camera()

    var body: some View {
        HStack(spacing: 0) {
            camera.preview
                .onAppear { Task { await camera.start() } }
            ConfigurationView(camera: camera)
        }
    }
}

The source combines model and service responsibilities in Camera. “MVVM-style” is an inference from a view-owned observable model, not an explicit project label.

Ownership and state

classDiagram
    ContentView *-- Camera
    Camera *-- AVCaptureSession
    Camera *-- PreferredCameraObserver
    Camera *-- VideoEffectsObserver
    Camera *-- CameraPreview
    Camera --> Device : publishes selections
    Camera --> VideoFormat : publishes selections

Ownership evidence

ContinuityCam/Camera.swift:29 — session and observer ownership sits inside Camera (abridged).

private(set) var isSetup = false
private(set) var isAuthorized = false
private(set) var isRunning = false
private let session = AVCaptureSession()
private let preferredCameraObserver = PreferredCameraObserver()
private let videoEffectsObserver = VideoEffectsObserver()
private var subscriptions = Set<AnyCancellable>()

Class and protocol design

classDiagram
    Camera --> PreferredCameraObserver : subscribes
    Camera --> VideoEffectsObserver : subscribes
    PreferredCameraObserver --> AVCaptureDevice : KVO
    VideoEffectsObserver --> AVCaptureDevice : KVO
    CameraPreview ..|> NSViewRepresentable

Reference code

ContinuityCam/Camera.swift:97 — KVO bridge objects feed the observable model through Combine (abridged).

preferredCameraObserver.$systemPreferredCamera
    .dropFirst().removeDuplicates().compactMap({ $0 })
    .sink { [weak self] captureDevice in
        guard let self = self, self.isSetup else { return }
        Task { await self.systemPreferredCameraChanged(to: captureDevice) }
    }.store(in: &subscriptions)

videoEffectsObserver.$isCenterStageEnabled
    .receive(on: RunLoop.main)
    .assign(to: \.isCenterStageEnabled, on: self)
    .store(in: &subscriptions)

There is no app-defined protocol boundary. Instead, small observer classes bridge static AVCaptureDevice KVO into Combine, while CameraPreview bridges AppKit into SwiftUI.

Access control

ContinuityCam/DeviceObservers.swift:41:

class PreferredCameraObserver: NSObject, ObservableObject {
    private let systemPreferredKeyPath = "systemPreferredCamera"
    @Published private(set) var systemPreferredCamera: AVCaptureDevice?
}

Logic ownership and placement

Design patterns

Naming conventions

• Role nouns are direct: Camera, CameraPreview, ConfigurationView, PreferredCameraObserver.
• Boolean state uses is...Enabled, is...Supported, isSetup, and isRunning.
• Methods distinguish setup (setupInputs) from selection (selectCaptureDevice) and derived-state updates (updateVideoEffectsState).
• Primary SwiftUI/AppKit adapters live under Views; model-supporting value types remain with Camera.

Architecture takeaways

• A small sample can use one observable camera owner without a separate service layer when capture scope is narrow.
• Use private(set) for system-derived UI state and writable published properties only for real user intent.
• Isolate KVO and native-view bridging in small adapter objects/files.
• The sample demonstrates preview and configuration; it does not implement photo/movie output persistence.

Source map

• Official Apple documentation