Configuring the PencilKit tool picker

At a glance

Project structure

Source bundle/
├── PencilKitCustomToolPicker/
│   ├── AppDelegate.swift
│   ├── AttributeViewController.swift
│   ├── SignatureViewController.swift
│   ├── DrawingViewController.swift
│   ├── AnimalStampWrapper.swift
│   ├── CustomPickerItemImageProviding.swift
│   ├── StampGestureRecognizer.swift
│   └── Base.lproj/
│       ├── LaunchScreen.storyboard
│       └── Main.storyboard
├── Configuration/
│   └── SampleCode.xcconfig
└── PencilKitCustomToolPicker.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 13 source declaration(s).

Overall architecture

flowchart LR
    N1["AppDelegate"]
    N2["AttributeViewController"]
    N3["Model"]
    N4["ImageProvider"]
    N5["PencilKit APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4
    N4 --> N5

Reference code

PencilKitCustomToolPicker/AppDelegate.swift:10 — architecture anchor

@main
class AppDelegate: UIResponder, UIApplicationDelegate {
    var window: UIWindow?
}

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
    AppDelegate o-- UIWindow : window
    AttributeViewController o-- Model : attributeModel
    AttributeViewController o-- UICollectionView : collectionView
    Model *-- Array : attributes

Ownership evidence

PencilKitCustomToolPicker/AppDelegate.swift:12 — stored dependency or nearest verified ownership anchor

@main
class AppDelegate: UIResponder, UIApplicationDelegate {
    var window: UIWindow?
}

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.

Class and protocol design

PencilKitCustomToolPicker/SignatureViewController.swift:11 — representative type boundary

@MainActor protocol SignatureViewControllerDelegate: NSObjectProtocol {
    var signature: PKDrawing { get set }
}

The source explicitly defines local protocol relationships: ImageProvider → CustomPickerItemImageProviding, DrawingViewController → SignatureViewControllerDelegate.

Access control

Reference code

PencilKitCustomToolPicker/AttributeViewController.swift:198 — representative boundary

        private func buttonTapped() {
            action?(name)
        }

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: AttributeViewController, DrawingViewController, SignatureViewController; Delegate: AppDelegate, SignatureViewControllerDelegate; Model: Model; Provider: ImageProvider.
• Protocols: SignatureViewControllerDelegate, CustomPickerItemImageProviding.
• Methods: reload, viewDidLoad, collectionView, addSubview, prepareForReuse, buttonTapped, setSelected, removeBorder.
• Files: PencilKitCustomToolPicker/AppDelegate.swift, PencilKitCustomToolPicker/AttributeViewController.swift, PencilKitCustomToolPicker/SignatureViewController.swift, PencilKitCustomToolPicker/DrawingViewController.swift, PencilKitCustomToolPicker/AnimalStampWrapper.swift, PencilKitCustomToolPicker/CustomPickerItemImageProviding.swift.

Architecture takeaways

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