AVCam: Building a camera app

At a glance

Project structure

Source bundle/
├── AVCam/
│   ├── AVCamApp.swift
│   ├── Model/
│   │   └── DataTypes.swift
│   ├── Views/
│   │   ├── Toolbars/
│   │   │   └── MainToolbar/
│   │   │       └── CaptureButton.swift
│   │   └── CameraPreview.swift
│   ├── CameraView.swift
│   ├── CaptureService.swift
│   ├── Preview Content/
│   │   └── PreviewCameraModel.swift
│   ├── CameraModel.swift
│   └── Capture/
│       ├── PhotoCapture.swift
│       └── SPCObserver.swift
├── AVCamCaptureExtension/
│   └── AVCamCaptureExtension.swift
└── AVCamControlCenterExtension/
    └── AVCamControlCenterExtensionBundle.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 59 source declaration(s).

Overall architecture

flowchart LR
    Bundle["Sample bundle"]
    V1["AVCam"]
    V2["AVCamCaptureExtension"]
    V3["AVCamControlCenterExtension"]
    Boundary["AVFoundation APIs"]
    Bundle --> V1
    V1 --> Boundary
    Bundle --> V2
    V2 --> Boundary
    Bundle --> V3
    V3 --> Boundary

Reference code

AVCam/AVCamApp.swift:11 — architecture anchor

@main
/// The AVCam app's main entry point.
struct AVCamApp: App {

    // Simulator doesn't support the AVFoundation capture APIs. Use the preview camera when running in Simulator.
    @State private var camera = CameraModel()

    // An indication of the scene's operational state.
    @Environment(\.scenePhase) var scenePhase

    var body: some Scene {
        WindowGroup {
            CameraView(camera: camera)
                .statusBarHidden(true)
                .task {
                    // Start the capture pipeline.
                    await camera.start()
                }
                // Monitor the scene phase. Synchronize the persistent state when
                // the camera is running and the app becomes active.
                .onChange(of: scenePhase) { _, newPhase in
                    guard camera.status == .running, newPhase == .active else { return }
                    Task { @MainActor in
                        await camera.syncState()
                    }
                }
        }
    }
}

Interpretation

The branches represent separate entry-bearing project variants in the downloaded bundle, not runtime calls between those variants. Each branch is intentionally collapsed at the documented framework boundary; the detailed target-local flow remains in the cited files. Ownership is claimed only where the next section cites a stored property or assignment.

Ownership and state

classDiagram
    AVCamApp *-- CameraModel : camera
    AVCamApp *-- Logger : logger
    Photo *-- Data : data
    Photo *-- Bool : isProxy

Ownership evidence

AVCam/AVCamApp.swift:16 — stored dependency or nearest verified ownership anchor

struct AVCamApp: 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

AVCam/AVCamApp.swift:27 — representative execution boundary

struct AVCamApp: App {
    // ...
                    await camera.start()
    // ...
}

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

AVCam/Model/DataTypes.swift:147 — representative type boundary

protocol OutputService {
    associatedtype Output: AVCaptureOutput
    // ...
}

The source explicitly defines local protocol relationships: CameraModel → Camera, MovieCapture → OutputService, PhotoCapture → OutputService, PreviewCameraModel → Camera, PreviewSourceStub → PreviewSource, PreviewView → PreviewTarget.

Access control

Reference code

AVCam/AVCamApp.swift:16 — representative boundary

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

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
    actor User
    participant View as CameraView
    participant Model as CameraModel
    participant Service as CaptureService
    participant Photo as PhotoCapture
    participant Library as MediaLibrary
    User->>View: Tap shutter
    View->>Model: capturePhoto()
    Model->>Service: capturePhoto(features)
    Service->>Photo: capturePhoto(features)
    Photo-->>Model: Photo
    Model->>Library: save(photo)
    Library-->>Model: thumbnail stream update
    Model-->>View: observable thumbnail/activity

Reference code

AVCam/CameraModel.swift:154 — capturePhoto

    func capturePhoto() async {
        do {
            let photo = try await captureService.capturePhoto(with: currentPhotoFeatures)
            try await mediaLibrary.save(photo: photo)
        } catch {
            self.error = error
        }
    }

Naming conventions

• Types: App: AVCamApp; Delegate: CaptureControlsDelegate, MovieCaptureDelegate, PhotoCaptureDelegate, ReadinessDelegate; Model: CameraModel, PreviewCameraModel; Observer: SystemPreferredCameraObserver; Service: CaptureService, OutputService; View: CameraView, CaptureModeView, PlatformView, PreviewView, RecordingTimeView.
• Protocols: OutputService, PlatformView, PreviewSource, PreviewTarget, Camera.
• Methods: updateConfiguration, setVideoRotationAngle, makeBody, start, setUpSession, addInput, addOutput, configureControls.
• Files: AVCam/AVCamApp.swift, AVCamCaptureExtension/AVCamCaptureExtension.swift, AVCamControlCenterExtension/AVCamControlCenterExtensionBundle.swift, AVCam/Views/Toolbars/MainToolbar/CaptureButton.swift, AVCam/CameraView.swift, AVCam/CaptureService.swift.

Architecture takeaways

• AVCamApp is the main source-visible entry or composition anchor for this sample.
• Framework work reaches SwiftUI, AVFoundation, AppIntents, LockedCameraCapture 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