AVCamBarcode: detecting barcodes and faces

At a glance

Project structure

Source bundle/
├── AVCamBarcode/
│   ├── AppDelegate.swift
│   ├── CameraViewController.swift
│   ├── ItemSelectionViewController.swift
│   ├── PreviewView.swift
│   ├── Base.lproj/
│   │   ├── LaunchScreen.storyboard
│   │   └── Main.storyboard
│   └── Info.plist
├── AVCamBarcode.xcodeproj/
│   ├── .xcodesamplecode.plist
│   └── project.pbxproj
└── Configuration/
    └── SampleCode.xcconfig

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 8 source declaration(s).

Overall architecture

flowchart LR
    N1["AppDelegate"]
    N2["CameraViewController"]
    N3["AVFoundation APIs"]
    N1 --> N2
    N2 --> N3

Reference code

AVCamBarcode/AppDelegate.swift:10 — architecture anchor

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

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 AVFoundation.

Ownership and state

classDiagram
    AppDelegate o-- UIWindow : window
    CameraViewController o-- Setupresult : setupResult
    CameraViewController o-- Issessionrunning : isSessionRunning
    CameraViewController *-- AVCaptureSession : session

Ownership evidence

AVCamBarcode/AppDelegate.swift:12 — 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

AVCamBarcode/CameraViewController.swift:86 — representative execution boundary

                DispatchQueue.main.async {
                    let changePrivatySetting = "AVCamBarcode doesn't have permission to use the camera, please change privacy settings"
                    let message = NSLocalizedString(changePrivatySetting, comment: "Alert message when the user has denied access to the camera")
                    // ...
                }

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

AVCamBarcode/ItemSelectionViewController.swift:10 — representative type boundary

protocol ItemSelectionViewControllerDelegate: AnyObject {
    func itemSelectionViewController<Item>(_ itemSelectionViewController: ItemSelectionViewController<Item>,
                                           didFinishSelectingItems selectedItems: [Item])
}

The source explicitly defines local protocol relationships: CameraViewController → ItemSelectionViewControllerDelegate.

Access control

Reference code

AVCamBarcode/CameraViewController.swift:173 — representative boundary

class CameraViewController: UIViewController, AVCaptureMetadataOutputObjectsDelegate, ItemSelectionViewControllerDelegate {
    // ...
    private let session = AVCaptureSession()
    // ...
}

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 Output as Metadata output
    participant Controller as CameraViewController
    participant Main as Main queue
    participant Preview as Preview layer
    Output->>Controller: didOutput metadataObjects
    Controller->>Controller: nonblocking semaphore wait
    Controller->>Main: transform objects and build layers
    Main->>Preview: replace overlay layers
    Main->>Controller: signal semaphore

Reference code

AVCamBarcode/CameraViewController.swift:792 — metadataOutput

    func metadataOutput(_ output: AVCaptureMetadataOutput, didOutput metadataObjects: [AVMetadataObject], from connection: AVCaptureConnection) {
        // Drop new notifications if old ones are still processing using `wait()`, to avoid queueing up stale data.
        if metadataObjectsOverlayLayersDrawingSemaphore.wait(timeout: .now()) == .success {
            DispatchQueue.main.async {
                self.removeMetadataObjectOverlayLayers()

                var metadataObjectOverlayLayers = [MetadataObjectLayer]()
                for metadataObject in metadataObjects {
                    let metadataObjectOverlayLayer = self.createMetadataObjectOverlayWithMetadataObject(metadataObject)
                    metadataObjectOverlayLayers.append(metadataObjectOverlayLayer)
                }

                self.addMetadataObjectOverlayLayersToVideoPreviewView(metadataObjectOverlayLayers)

                self.metadataObjectsOverlayLayersDrawingSemaphore.signal()
            }
        }
    }

Naming conventions

• Types: Controller: CameraViewController, ItemSelectionViewController; Delegate: AppDelegate, ItemSelectionViewControllerDelegate; View: PreviewView.
• Protocols: ItemSelectionViewControllerDelegate.
• Methods: viewDidLoad, viewWillAppear, viewWillDisappear, viewWillTransition, configureSession, availableSessionPresets, selectSessionPreset, changeCamera.
• Files: AVCamBarcode/AppDelegate.swift, AVCamBarcode/CameraViewController.swift, AVCamBarcode/ItemSelectionViewController.swift, AVCamBarcode/PreviewView.swift.

Architecture takeaways

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