Adding hardware keyboard support to your app

At a glance

Project structure

ProIllustratorSample/
├── AppDelegate.swift
├── SceneDelegate.swift
├── MainViewController.swift
├── FileListViewController.swift
├── GlobalKeyboardShortcutRespondable.swift
├── Model.swift
└── Canvas/
    ├── CanvasViewController.swift
    ├── AddShapeViewController.swift
    ├── ShapeView.swift
    └── ShapeSelectionView.swift

Structure observations

• Root composition is programmatic; no storyboard owns the screen graph.
• The global-command protocol is separate because AppDelegate defines commands while active child responders implement effects.
• Raw-key and gesture movement share the canvas’s selection/movement state.

Overall architecture

flowchart LR
    Scene["SceneDelegate"] --> Main["MainViewController"]
    Main --> Files["FileListViewController"]
    Main --> Canvas["CanvasViewController"]
    Files -. weak delegate .-> Main
    Main -->|selected file| Canvas
    App["AppDelegate.buildMenu"] --> Commands["UIKeyCommand selectors"]
    Commands -. responder chain .-> Capability["GlobalKeyboardShortcutRespondable"]
    Files ..-> Capability
    Canvas ..-> Capability
    Files --> Store["FileStore"]
    Canvas --> Model["IllustrationFile and Shape"]

Reference code

ProIllustratorSample/MainViewController.swift:11 — the split controller owns both children and translates file selection into canvas state.

class MainViewController: UISplitViewController, FileListViewControllerDelegate {
    let fileListViewController = FileListViewController(style: .plain)
    let canvasViewController = CanvasViewController(nibName: nil, bundle: nil)

    override init(nibName: String?, bundle: Bundle?) {
        super.init(nibName: nil, bundle: nil)
        fileListViewController.delegate = self
        viewControllers = [UINavigationController(rootViewController: fileListViewController),
                           UINavigationController(rootViewController: canvasViewController)]
    }
}

Interpretation

UIKit’s responder chain is the command bus. The app publishes selectors globally, but the first active child that conforms and can perform the action becomes the handler; the root does not manually switch on focus.

Ownership and state

classDiagram
    SceneDelegate *-- MainViewController : creates
    MainViewController *-- FileListViewController : owns
    MainViewController *-- CanvasViewController : owns
    FileListViewController *-- FileStore : owns value
    FileStore *-- IllustrationFile : stores
    IllustrationFile *-- Shape : stores
    CanvasViewController o-- IllustrationFile : selected reference
    CanvasViewController *-- ShapeView : creates for shapes
    AddShapeViewController o-- AddShapeViewControllerDelegate : weak
    FileListViewController o-- FileListViewControllerDelegate : weak

Ownership evidence

ProIllustratorSample/FileListViewController.swift:15 — the list owns its store/data source but delegates selection without retaining the root.

class FileListViewController: UITableViewController {
    var store = FileStore()
    weak var delegate: FileListViewControllerDelegate?
    var tableViewDataSource: UITableViewDiffableDataSource<Int, Int>?
}

Class and protocol design

The optional @objc capability is deliberate: each responder implements only commands meaningful in its current context, and canPerformAction controls availability.

Access control

Reference code

ProIllustratorSample/Canvas/CanvasViewController.swift:195 — raw-key translation and movement mechanics remain private to the canvas.

private func movementDirectionForKeyPresses(_ presses: Set<UIPress>) -> UIRectEdge? {
    guard let key = presses.first?.key else { return nil }
    switch key.keyCode {
        case .keyboardLeftArrow: return .left
        case .keyboardDownArrow: return .bottom
        case .keyboardUpArrow: return .top
        case .keyboardRightArrow: return .right
        default: return nil
    }
}

Logic ownership and placement

Design patterns

Naming conventions

• ...Respondable names a responder-chain capability; delegate protocols name the source controller.
• User commands use standard responder verbs: createNewItem, deleteSelectedItem, and selectAll.
• Input-state helpers use directional verbs such as startMoving... and stopMoving....
• Canvas/ groups the view, controller, and modal needed by one feature.

Architecture takeaways

• Put global shortcuts in the application menu, but let focus and the responder chain choose the handler.
• Use canPerformAction to express contextual command availability.
• Keep raw-key state, gesture state, and model commits in the same interaction owner.
• Use weak delegates for child-to-parent events and strong ownership from parent to child.

Source map

• Official Apple documentation