AppDelegate.swift

import Cocoa
import AXSwift

class AppDelegate: NSObject, NSApplicationDelegate {

    var observer: Observer!

    func applicationDidFinishLaunching(_ aNotification: Notification) {
        let app = Application.allForBundleID("com.apple.finder").first!

        do {
            try startWatcher(app)
        } catch let error {
            NSLog("Error: Could not watch app [\(app)]: \(error)")
            abort()
        }
    }

    func startWatcher(_ app: Application) throws {
        var updated = false
        observer = app.createObserver { (observer: Observer, element: UIElement, event: AXNotification, info: [String: AnyObject]?) in
            var elementDesc: String!
            if let role = try? element.role()!, role == .window {
                elementDesc = "\(element) \"\(try! (element.attribute(.title) as String?)!)\""
            } else {
                elementDesc = "\(element)"
            }
            print("\(event) on \(String(describing: elementDesc)); info: \(info ?? [:])")

            // Watch events on new windows
            if event == .windowCreated {
                do {
                    try observer.addNotification(.uiElementDestroyed, forElement: element)
                    try observer.addNotification(.moved, forElement: element)
                } catch let error {
                    NSLog("Error: Could not watch [\(element)]: \(error)")
                }
            }

            // Group simultaneous events together with --- lines
            if !updated {
                updated = true
                // Set this code to run after the current run loop, which is dispatching all notifications.
                DispatchQueue.main.async {
                    print("---")
                    updated = false
                }
            }
        }

        try observer.addNotification(.windowCreated, forElement: app)
        try observer.addNotification(.mainWindowChanged, forElement: app)
    }

    func applicationWillTerminate(_ aNotification: Notification) {
        // Insert code here to tear down your application
    }

}