Enhancing your iPad app with pointer interactions

At a glance

Project structure

QuiltSimulator/
├── ViewController.swift
├── QuiltView.swift
├── ThreadPickerViewController.swift
├── PatchworkView.swift
├── ColorBlockView.swift
├── AppDelegate.swift
├── SceneDelegate.swift
└── Base.lproj/Main.storyboard

Structure observations

• The main screen coordinates menus and tool selection but does not store stitch locations.
• The thread picker contains its cell because the cell’s lift effect is local to that feature.
• PatchworkView and ColorBlockView build the decorative background independently from the editable stitch overlay.

Overall architecture

flowchart LR
    Main["ViewController"] --> Quilt["QuiltView"]
    Main --> Picker["ThreadPickerViewController"]
    Picker -->|weak delegate color| Main
    Main -->|stitchColor| Quilt
    Quilt --> Locations["stitchLocations"]
    Quilt --> ShapeLayer["CAShapeLayer"]
    Quilt --> Defaults["UserDefaults"]
    Quilt --> Pointer["UIPointerInteractionDelegate"]
    Picker --> Cells["ThreadCell pointer delegates"]
    Main --> ButtonProviders["UIButton pointerStyleProvider"]
    Quilt *-- Patchwork["PatchworkView"]
    Patchwork *-- Blocks["ColorBlockView"]

Reference code

QuiltSimulator/QuiltView.swift:62 — the editor view installs both its drawing input and pointer adapter with the state they affect.

func sharedInit() {
    let patchworkView = PatchworkView()
    patchworkView.translatesAutoresizingMaskIntoConstraints = false
    self.insertSubview(patchworkView, at: 0)
    patchworkView.centerXAnchor.constraint(equalTo: self.safeAreaLayoutGuide.centerXAnchor).isActive = true
    patchworkView.centerYAnchor.constraint(equalTo: self.safeAreaLayoutGuide.centerYAnchor).isActive = true

    self.addGestureRecognizer(UITapGestureRecognizer(target: self, action: #selector(self.handleTap(_:))))
    stitchLayer.lineWidth = 2
    stitchLayer.fillColor = UIColor.clear.cgColor
    stitchLayer.lineCap = .round
    self.layer.addSublayer(stitchLayer)

    self.addInteraction(UIPointerInteraction(delegate: self))
}

Interpretation

Pointer support is an enhancement of existing components, not a central service. Each component calculates a style from its own bounds and purpose, while the controller only provides button-specific closures and tool routing.

Ownership and state

classDiagram
    ViewController *-- UIButton : thread tool
    ViewController o-- QuiltView : storyboard outlet
    ViewController --> ThreadPickerViewController : presents
    ThreadPickerViewController o-- ThreadPickerViewControllerDelegate : weak
    ThreadPickerViewController *-- ThreadCell : collection cells
    QuiltView *-- CAShapeLayer : creates
    QuiltView *-- CGPoint : stitch locations
    QuiltView *-- PatchworkView : creates
    PatchworkView *-- ColorBlockView : creates
    QuiltView ..|> UIPointerInteractionDelegate
    ThreadCell ..|> UIPointerInteractionDelegate

Ownership evidence

QuiltSimulator/ThreadPickerViewController.swift:10 — selection leaves the picker through a class-bound weak delegate rather than direct knowledge of the main screen.

protocol ThreadPickerViewControllerDelegate: NSObjectProtocol {

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

Class and protocol design

ThreadPickerViewControllerDelegate is the only app-defined protocol. It reduces coupling to one UIColor result. Pointer and scroll behavior use UIKit protocols because those callbacks are driven by the framework.

Access control

Reference code

QuiltSimulator/QuiltView.swift:12 — persisted-key names are private, while the view exposes semantic mode and color properties to its controller.

private static let straightLineStitchUserDefaultsKey = "useStrightLineStitch"
private static let colorUserDefaultsKey = "threadColor"

var useStraightLineStitch: Bool {
    get { UserDefaults.standard.bool(forKey: QuiltView.straightLineStitchUserDefaultsKey) }
    set { UserDefaults.standard.set(newValue,
                                    forKey: QuiltView.straightLineStitchUserDefaultsKey) }
}

Logic ownership and placement

Design patterns

Naming conventions

• Types name visual roles: QuiltView, PatchworkView, ColorBlockView, and ThreadCell.
• Commands use domain verbs such as ripLastStitch, ripAllStitches, and threadPickerDidPickColor.
• useStraightLineStitch and stitchColor expose user concepts rather than storage keys.
• sharedInit signals the common initializer path for programmatic and storyboard creation.

Architecture takeaways

• Put pointer-region calculations beside the view geometry they describe.
• Use a weak, semantic delegate when a presented picker needs to return one result.
• Let the screen controller coordinate tools while the custom editor owns its durable interaction state.
• Compose decorative views separately when they do not participate in editing behavior.

Source map

• Official Apple documentation