Supporting coordinated media playback

At a glance

Project structure

Source bundle/
└── GroupWatching/
    ├── App/
    │   ├── AppDelegate.swift
    │   └── SceneDelegate.swift
    ├── UI/
    │   ├── MovieListViewController.swift
    │   ├── MovieDetailViewController.swift
    │   ├── MovieInfoViewController.swift
    │   ├── PosterImageView.swift
    │   └── ViewExtensions.swift
    ├── MoviePlayerViewController.swift
    ├── CoordinationManager.swift
    ├── MovieWatchingActivity.swift
    └── Model/
        ├── Library.swift
        └── Poster.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 6 project/configuration file(s) and 16 source declaration(s).

Overall architecture

flowchart LR
    N1["AppDelegate"]
    N2["MovieDetailViewController"]
    N3["CoordinationManager"]
    N4["AVFoundation APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4

Reference code

GroupWatching/App/AppDelegate.swift:11 — architecture anchor

@main
class AppDelegate: UIResponder, UIApplicationDelegate {

    func application(_ application: UIApplication,
                     didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]? = nil) -> Bool {
        do {
            // Configure the audio session for movie playback.
            try AVAudioSession.sharedInstance().setCategory(.playback, mode: .moviePlayback)
        } catch {
            print("Unable to set the audio session category: \(error)")
        }

        return true
    }
}

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
    MovieListViewController o-- Subscriptions : subscriptions
    MovieListViewController o-- UICollectionView : collectionView
    MovieListViewController o-- UICollectionViewDiffableDataSource : dataSource
    MoviePlayerViewController o-- AVCoordinatedPlaybackSuspension : whatHappened

Ownership evidence

GroupWatching/UI/MovieListViewController.swift:13 — stored dependency or nearest verified ownership anchor

class MovieListViewController: UIViewController {
    // ...
    private var subscriptions = Set<AnyCancellable>()
    // ...
}

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

GroupWatching/CoordinationManager.swift:24 — representative execution boundary

        Task {
            // ...
                self.groupSession = groupSession
            // ...
        }

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

GroupWatching/App/AppDelegate.swift:12 — representative type boundary

@main
class AppDelegate: UIResponder, UIApplicationDelegate {
    // ...
            try AVAudioSession.sharedInstance().setCategory(.playback, mode: .moviePlayback)
    // ...
}

No local protocol conformance is claimed as protocol-oriented design; external framework conformances are listed only as dependencies.

Access control

Reference code

GroupWatching/App/SceneDelegate.swift:22 — representative boundary

    private func createWindow(for windowScene: UIWindowScene) -> UIWindow {
        // ...
        let list = MovieListViewController()
        // ...
    }

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: MovieDetailViewController, MovieInfoViewController, MovieListViewController, MoviePlayerViewController; Delegate: AppDelegate, SceneDelegate; Manager: CoordinationManager; View: PosterImageView.
• Protocols: no local protocol declaration in the scanned source.
• Methods: application, viewDidLoad, selectRow, configureDataSource, collectionView, updateConfiguration, configuration, performWhatHappened.
• Files: GroupWatching/App/AppDelegate.swift, GroupWatching/UI/MovieListViewController.swift, GroupWatching/MoviePlayerViewController.swift, GroupWatching/App/SceneDelegate.swift, GroupWatching/CoordinationManager.swift, GroupWatching/UI/MovieDetailViewController.swift.

Architecture takeaways

• AppDelegate is the main source-visible entry or composition anchor for this sample.
• Framework work reaches UIKit, GroupActivities, AVFoundation, AVKit 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.
• The source does not justify labeling the design protocol-oriented.

Source map

• Official Apple documentation