Building a handwriting recognition experience with PencilKit

At a glance

Project structure

Source bundle/
├── HandwritingRecognitionTutor/
│   ├── HandwritingRecognitionTutorApp.swift
│   ├── FlashcardView.swift
│   ├── CanvasView.swift
│   ├── ContentView.swift
│   ├── Flashcard.swift
│   ├── TutorModel.swift
│   └── GeometryHelpers.swift
├── Configuration/
│   └── SampleCode.xcconfig
└── HandwritingRecognitionTutor.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 3 project/configuration file(s) and 19 source declaration(s).

Overall architecture

flowchart LR
    N1["HandwritingRecognitionTutorApp"]
    N2["ContentView"]
    N3["Coordinator"]
    N4["PencilKit APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4

Reference code

HandwritingRecognitionTutor/HandwritingRecognitionTutorApp.swift:10 — architecture anchor

@main
struct HandwritingRecognitionTutorApp: App {
    var body: some Scene {
        WindowGroup {
            ContentView()
        }
    }
}

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 PencilKit.

Ownership and state

classDiagram
    FlashcardCarouselView o-- TutorModel : model
    FlashcardCarouselView *-- Task : runningTask
    FreeInputView *-- String : recognizedText
    FlashcardView o-- Flashcard : flashcard

Ownership evidence

HandwritingRecognitionTutor/FlashcardView.swift:14 — stored dependency or nearest verified ownership anchor

struct FlashcardCarouselView: View {
    @Bindable var model: TutorModel
    // ...
}

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

HandwritingRecognitionTutor/CanvasView.swift:74 — representative execution boundary

    @MainActor
    final class Coordinator: NSObject, PKCanvasViewDelegate {
        let model: TutorModel
        // ...
    }

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

HandwritingRecognitionTutor/HandwritingRecognitionTutorApp.swift:11 — representative type boundary

@main
struct HandwritingRecognitionTutorApp: App {
    // ...
            ContentView()
    // ...
}

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

Access control

Reference code

HandwritingRecognitionTutor/ContentView.swift:11 — representative boundary

struct ContentView: View {
    @State private var model = TutorModel()
    // ...
}

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: App: HandwritingRecognitionTutorApp; Coordinator: Coordinator; Model: TutorModel; View: CanvasView, CanvasWrapperView, ConfettiView, ContentView, FlashcardCarouselView.
• Protocols: no local protocol declaration in the scanned source.
• Methods: cardChrome, path, startTask, effectValue, makeUIView, updateUIView, makeCoordinator, canvasViewDrawingDidChange.
• Files: HandwritingRecognitionTutor/HandwritingRecognitionTutorApp.swift, HandwritingRecognitionTutor/FlashcardView.swift, HandwritingRecognitionTutor/CanvasView.swift, HandwritingRecognitionTutor/ContentView.swift, HandwritingRecognitionTutor/Flashcard.swift, HandwritingRecognitionTutor/TutorModel.swift.

Architecture takeaways

• HandwritingRecognitionTutorApp is the main source-visible entry or composition anchor for this sample.
• Framework work reaches SwiftUI, PencilKit, CoreGraphics, 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.
• The source does not justify labeling the design protocol-oriented.

Source map

• Official Apple documentation