Programmatically creating menus with Swift 3 and Cocoa - macos

Question

I am trying my hand at creating a Cocoa GUI app programmatically (i.e. without a nib file) using Swift 3. I've run into trouble getting the application's menus to show.
I would expect the below code to show a File menu items on the menu bar. Instead, while the window launches and works as expected, the code to set the menu seems to have no effect:
import AppKit
final class ApplicationController: NSObject, NSApplicationDelegate {
var mainWindow: NSWindow?
func applicationDidFinishLaunching(_ aNotification: Notification) {
let mainMenu = NSMenu()
let mainMenuFileItem = NSMenuItem(title: "File", action: nil, keyEquivalent: "")
let fileMenu = NSMenu(title: "File")
fileMenu.addItem(withTitle: "New...", action: nil, keyEquivalent: "n")
mainMenuFileItem.submenu = fileMenu
mainMenu.addItem(mainMenuFileItem)
NSApp.mainMenu = mainMenu
let window = NSWindow(contentRect: NSRect(x: 0, y: 0, width: 800, height: 600),
styleMask: [.titled, .closable, .resizable, .miniaturizable],
backing: NSBackingStoreType.buffered, defer: false)
window.orderFrontRegardless()
window.title = "Hello World"
self.mainWindow = window
NSApp.activate(ignoringOtherApps: true)
}
func applicationWillTerminate(_ aNotification: Notification) {
print("terminating")
}
func applicationShouldTerminateAfterLastWindowClosed(_ app: NSApplication) -> Bool{
return true
}
}
let app = NSApplication.shared()
let controller = ApplicationController()
app.delegate = controller
app.run()
The closest I've found to a working example is this answer. However, it appears to be for an earlier version of Swift/Cocoa, and I am not able to get that example working.
What am I doing wrong?

Answer 1

One needs to call NSApp.setActivationPolicy(.regular) to make the application a "regular" one. Making that call before app.run() fixes the issue of no menu showing.
The "main" part of the code should thus be:
let app = NSApplication.shared()
NSApp.setActivationPolicy(.regular)
let controller = ApplicationController()
app.delegate = controller
app.run()