Creating a Slideshow Project Extension for Photos

At a glance

Project structure

Source bundle/
├── Photos Project Slideshow/
│   └── AppDelegate.swift
└── Slideshow Sample/
    ├── Model/
    │   ├── ProjectModel.swift
    │   ├── AssetModel.swift
    │   └── ProjectModel+Persistence.swift
    ├── Grid/
    │   ├── CollectionViewDataSource.swift
    │   ├── GridViewController.swift
    │   └── AssetCollectionViewItem.swift
    ├── PhotoProjectViewController.swift
    └── Slides/
        ├── SimpleImageView.swift
        ├── SlideViewController.swift
        ├── SlideshowViewController.swift
        └── Animator.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 13 project/configuration file(s) and 13 source declaration(s).

Overall architecture

flowchart LR
    N1["AppDelegate"]
    N2["GridViewController"]
    N3["AssetModel"]
    N4["PhotosUI / Photos APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4

Reference code

Photos Project Slideshow/AppDelegate.swift:10 — architecture anchor

@NSApplicationMain
class AppDelegate: NSObject, NSApplicationDelegate {

    @IBOutlet weak var window: NSWindow!

    func applicationDidFinishLaunching(_ aNotification: Notification) {
        // Insert code here to initialize your application.
    }

    func applicationWillTerminate(_ aNotification: Notification) {
        // Insert code here to tear down your application.
    }

}

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 PhotosUI.

Ownership and state

classDiagram
    AppDelegate o-- NSWindow : window
    ProjectModel o-- PHProjectInfo : projectInfo
    CollectionViewDataSource *-- NSUserInterfaceItemIdentifier : reuseIdentifier
    GridViewController o-- NSCollectionView : collectionView

Ownership evidence

Photos Project Slideshow/AppDelegate.swift:13 — stored dependency or nearest verified ownership anchor

@NSApplicationMain
class AppDelegate: NSObject, NSApplicationDelegate {
    // ...
    @IBOutlet weak var window: NSWindow!
    // ...
}

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

Slideshow Sample/PhotoProjectViewController.swift:40 — representative execution boundary

        super.viewDidAppear()
        DispatchQueue.main.async {
            self.view.window?.makeFirstResponder(self)
        }

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

Slideshow Sample/Slides/Animator.swift:11 — representative type boundary

protocol AnimatableSlide {
    var contentAspectRatio: CGFloat? { get }
    var preferredZoomRect: CGRect? { get }
}

The source explicitly defines local protocol relationships: RoiZoomAnimator → Animator, SlideViewController → AnimatableSlide.

Access control

Reference code

Slideshow Sample/Slides/SlideViewController.swift:15 — representative boundary

class SlideViewController: NSViewController {
    // ...
    private var contentMode: PHImageContentMode = .aspectFit
    // ...
}

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: Controller: GridViewController, PhotoProjectViewController, SlideViewController, SlideshowViewController; DataSource: CollectionViewDataSource; Delegate: AppDelegate; Model: AssetModel, ProjectModel; View: SimpleImageView.
• Protocols: AnimatableSlide, Animator.
• Methods: applicationDidFinishLaunching, applicationWillTerminate, encode, collectionView, viewDidLoad, loadCollectionView, models, viewDidAppear.
• Files: Photos Project Slideshow/AppDelegate.swift, Slideshow Sample/Model/ProjectModel.swift, Slideshow Sample/Grid/CollectionViewDataSource.swift, Slideshow Sample/Grid/GridViewController.swift, Slideshow Sample/Model/AssetModel.swift, Slideshow Sample/PhotoProjectViewController.swift.

Architecture takeaways

• AppDelegate is the main source-visible entry or composition anchor for this sample.
• Framework work reaches Cocoa, PhotosUI, CoreGraphics, Photos 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