Modernize your AppKit app

// Modern dragging delegate methods
func tableView(_ tableView: NSTableView,
        pasteboardWriterForRow row: Int) -> (any NSPasteboardWriting)? {
    let pasteboardItem = NSPasteboardItem()
    pasteboardItem.setString(..., forType: .string)
    return pasteboardItem
}

// Use control events
let button = NSButton()
button.addTarget(
    self,
    action: #selector(trackingEndedOutsideHandler),
    for: .trackingEndedOutside
)

override func hitTest(_ point: NSPoint) -> NSView? {
    return nil
}

window.autorecalculatesKeyViewLoop = true

// Set the expanded interface delegate
@main class LightAppDelegate: NSObject, NSApplicationDelegate {
    lazy var lightStatusItem: NSStatusItem = { ... }()

    func applicationDidFinishLaunching(_ notification: Notification) {
        // ...
        lightStatusItem.expandedInterfaceDelegate = self
    }
}

// Implement the delegate methods
extension LightAppDelegate: NSStatusItemExpandedInterfaceDelegate {
    // ...
    func statusItem(_ statusItem: NSStatusItem, didBegin session:
                    NSStatusItemExpandedInterfaceSession) {
        // Show window
    }
    func statusItemDidEndExpandedInterfaceSession(
        _ statusItem: NSStatusItem, animated: Bool) {
        // Hide window
    }
    func selectedAction() {
        // Take the action
        // Cancel session to request window dismissal
        lightStatusItem.expandedInterfaceSession?.cancel()
    }
}

// Cancel the session when dismissing
extension LightAppDelegate: NSStatusItemExpandedInterfaceDelegate {
    // ...
    func statusItem(_ statusItem: NSStatusItem, didBegin session:
                    NSStatusItemExpandedInterfaceSession) {
        // Show window
    }
    func statusItemDidEndExpandedInterfaceSession(
        _ statusItem: NSStatusItem, animated: Bool) {
        // Hide window
    }
    func selectedAction() {
        // Take the action
        // Cancel session to request window dismissal
        lightStatusItem.expandedInterfaceSession?.cancel()
    }
}

window.preventsApplicationTerminationWhenModal = false

// Set window identifiers for state restoration
@MainActor class MainWindowController: NSWindowController, NSWindowDelegate {
    // ...
    convenience init() {
        let window = NSWindow( ... )
        // ...
        window.identifier = NSUserInterfaceItemIdentifier(WindowIdentifiers.mainWindow)
        window.setFrameAutosaveName(WindowIdentifiers.mainWindow)
        window.isRestorable = true
        window.restorationClass = WindowRestorationHandler.self
        // ...
    }
}

// Preserve state to recreate the UI
@MainActor class MainWindowController: NSWindowController, NSWindowDelegate {
    // ...
    override func encodeRestorableState(with coder: NSCoder) {
        super.encodeRestorableState(with: coder)
        // ...
        coder.encode(selectedProduct?.identifier.uuid,
                    forKey: RestorationKeys.productIdentifier)
        // ...
    }
    // ...
}

// Invalidate restorable state when the view hierarchy changes
@MainActor class MainWindowController: NSWindowController, NSWindowDelegate {
    // ...
    convenience init() {
        // ...
        splitViewController.onProductSelected = { [weak self] product in
            self?.invalidateRestorableState()
        }
    }
}

// Restore windows
class WindowRestorationHandler: NSObject, NSWindowRestoration {
    static func restoreWindow(
        withIdentifier identifier: NSUserInterfaceItemIdentifier,
        state: NSCoder,
        completionHandler: @escaping (NSWindow?, Error?) -> Void
    ) {
        //...
        if identifier == .mainWindow, let window = appDelegate.mainWindowController?.window {
            completionHandler(window, nil)
        } else if identifier == .imageWindow {
            let controller = ImageWindowController()
            appDelegate.imageWindowControllers.append(controller)
            completionHandler(controller.window, nil)
        } else {
            completionHandler(nil, error)
        }
    }
}

// Restore window UI
@MainActor class MainWindowController: NSWindowController, NSWindowDelegate {
    //...
    override func restoreState(with coder: NSCoder) {
        super.restoreState(with: coder)
        if let productId = coder.decodeObject(
            of: [NSString.self],
            forKey: RestorationKeys.productIdentifier) as? String {
            splitViewController?.selectedProductId = productId
        }
        //...
    }
}

// Subclass NSView to override cornerConfiguration
class LocalWeatherView: NSView {
    // ...
    override var cornerConfiguration: NSViewCornerConfiguration? {
        let radius: NSViewCornerRadius = .containerConcentric(minimumCornerRadius)
        return .uniformCorners(radius: radius)
    }
    // ...
}