Enhancing your iPad app with pointer interactions

At a glance

Project structure

Source bundle/
├── QuiltSimulator/
│   ├── AppDelegate.swift
│   ├── ThreadPickerViewController.swift
│   ├── ColorBlockView.swift
│   ├── PatchworkView.swift
│   ├── QuiltView.swift
│   ├── SceneDelegate.swift
│   ├── ViewController.swift
│   └── Base.lproj/
│       ├── LaunchScreen.storyboard
│       └── Main.storyboard
├── Configuration/
│   └── SampleCode.xcconfig
└── QuiltSimulator.xcodeproj/
    ├── .xcodesamplecode.plist
    └── project.pbxproj

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 9 source declaration(s).

Overall architecture

flowchart LR
    N1["AppDelegate"]
    N2["ThreadPickerViewController"]
    N3["UIKit APIs"]
    N1 --> N2
    N2 --> N3

Reference code

QuiltSimulator/AppDelegate.swift:10 — architecture anchor

@UIApplicationMain
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 {
        /** Called when a new scene session is being created.
            Use this method to select a configuration to create the new scene with.
        */
        return UISceneConfiguration(name: "Default Configuration", sessionRole: connectingSceneSession.role)
    }

    func application(_ application: UIApplication, didDiscardSceneSessions sceneSessions: Set<UISceneSession>) {
        /** Called when the user discards a scene session.
            If any sessions were discarded while the application was not running,
            this will be called shortly after application:didFinishLaunchingWithOptions.
            Use this method to release any resources that were specific to the discarded scenes, as they will not return.
        */
    }

}

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
    ThreadPickerViewController o-- ThreadPickerViewControllerDelegate : delegate
    ThreadPickerViewController o-- Colors : colors
    ThreadCell o-- UIView : swatch
    ColorBlockView *-- UIStackView : stackView

Ownership evidence

QuiltSimulator/ThreadPickerViewController.swift:17 — stored dependency or nearest verified ownership anchor

class ThreadPickerViewController: UICollectionViewController {
    // ...
    weak var delegate: ThreadPickerViewControllerDelegate?
    // ...
}

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

QuiltSimulator/ThreadPickerViewController.swift:10 — representative type boundary

protocol ThreadPickerViewControllerDelegate: NSObjectProtocol {

    func threadPickerDidPickColor(_ threadPicker: ThreadPickerViewController, color: UIColor)
}

The source explicitly defines local protocol relationships: ViewController → ThreadPickerViewControllerDelegate.

Access control

Reference code

QuiltSimulator/QuiltView.swift:12 — representative boundary

class QuiltView: UIView, UIPointerInteractionDelegate {
    // ...
    private static let straightLineStitchUserDefaultsKey = "useStrightLineStitch"
    private static let colorUserDefaultsKey = "threadColor"

    // ...
}

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: ThreadPickerViewController, ViewController; Delegate: AppDelegate, SceneDelegate, ThreadPickerViewControllerDelegate; View: ColorBlockView, PatchworkView, QuiltView.
• Protocols: ThreadPickerViewControllerDelegate.
• Methods: application, threadPickerDidPickColor, numberOfSections, collectionView, sharedInit, layoutSubviews, pointerInteraction, crosshairBezierPath.
• Files: QuiltSimulator/AppDelegate.swift, QuiltSimulator/ThreadPickerViewController.swift, QuiltSimulator/ColorBlockView.swift, QuiltSimulator/PatchworkView.swift, QuiltSimulator/QuiltView.swift, QuiltSimulator/SceneDelegate.swift.

Architecture takeaways

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