Building and improving your app with Mac Catalyst

At a glance

Project structure

Source bundle/
└── Trip Planner/
    ├── AppDelegate.swift
    ├── Model/
    │   └── DataModel.swift
    ├── SidebarViewController.swift
    ├── Printing/
    │   └── ItemPrintPageRenderer.swift
    ├── SupplementaryViewController.swift
    ├── Item Detail/
    │   ├── DetailSceneDelegate.swift
    │   ├── RewardsProgramDetailViewController.swift
    │   ├── DetailViewController.swift
    │   ├── LocatedItemDetailViewController.swift
    │   └── SharingImageView.swift
    ├── SceneDelegate.swift
    └── BrowserSplitViewController.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 9 project/configuration file(s) and 38 source declaration(s).

Overall architecture

flowchart LR
    N1["AppDelegate"]
    N2["BrowserSplitViewController"]
    N3["DetailToolbarModel"]
    N4["ItemPrintPageRenderer"]
    N5["UIKit APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4
    N4 --> N5

Reference code

Trip Planner/AppDelegate.swift:10 — architecture anchor

@main
class AppDelegate: UIResponder, UIApplicationDelegate {

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        // Override point for customization after application launch.
        return true
    }
    // MARK: UISceneSession Lifecycle

    func application(_ application: UIApplication,
                     configurationForConnecting connectingSceneSession: UISceneSession,
                     options: UIScene.ConnectionOptions) -> UISceneConfiguration {
        if let activity = options.userActivities.first, activity.activityType == DetailSceneDelegate.activityType {
            let config = UISceneConfiguration(name: "DetailViewer", sessionRole: connectingSceneSession.role)
            return config
        }
        return UISceneConfiguration(name: "Default Configuration", sessionRole: connectingSceneSession.role)
    }
}

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 UIKit.

Ownership and state

classDiagram
    Country o-- ItemID : itemID
    Country *-- String : name
    Country *-- Array : lodgings
    Country *-- Array : restaurants

Ownership evidence

Trip Planner/Model/DataModel.swift:39 — stored dependency or nearest verified ownership anchor

struct Country: ModelItem, IconNameProviding {
    let itemID: ItemID
    // ...
}

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.

No source-visible execution, scheduling, or synchronization boundary was found in the indexed source.

@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.

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

Trip Planner/Model/DataModel.swift:12 — representative type boundary

protocol Model {
    var countries: [Country] { get }
    var rewardsPrograms: [RewardsProgram] { get }
}

The source explicitly defines local protocol relationships: Country → ModelItem, Country → IconNameProviding, Lodging → IconNameProviding, Restaurant → IconNameProviding, Sight → IconNameProviding, RewardsProgram → ModelItem.

Access control

Reference code

Trip Planner/BrowserSplitViewController.swift:11 — representative boundary

class BrowserSplitViewController: UISplitViewController {
    private(set) var selectedItemsCollection = ModelItemsCollection()
    // ...
}

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: BrowserSplitViewController, DetailViewController, LocatedItemDetailViewController, RewardsProgramDetailViewController, SidebarViewController; Delegate: AppDelegate, DetailSceneDelegate, SceneDelegate; Model: DetailToolbarModel, MainSceneToolbarModel, Model; Renderer: ItemPrintPageRenderer; View: SharingImageView.
• Protocols: Model, ItemIdentifierProviding, ImageProviding, LocationProviding, IconNameProviding, ModelItem, ImageNaming.
• Methods: application, isEqual, item, findItem, children, hash, loadView, addCountriesToSnapshot.
• Files: Trip Planner/AppDelegate.swift, Trip Planner/SidebarViewController.swift, Trip Planner/Printing/ItemPrintPageRenderer.swift, Trip Planner/SupplementaryViewController.swift, Trip Planner/Item Detail/DetailSceneDelegate.swift, Trip Planner/Item Detail/RewardsProgramDetailViewController.swift.

Architecture takeaways

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