Xcode NSStatusBar Item not appearing - swift

Question

I'm trying to add an item to the status bar, but when I launch the app the item only appears in the top left for a split second and then quickly disappears.
I've looked through the documentation and I can see things have changed recently e.g. statusItem.title has become statusItem.button?.title. But don't seem to be missing anything else. Any help?
Here's my code:
var statusItem : NSStatusItem? = nil
func applicationDidFinishLaunching(_ aNotification: Notification) {
// Insert code here to initialize your application
let statusItem = NSStatusBar.system.statusItem(withLength: NSStatusItem.variableLength)
statusItem.button?.title = "Connect!"
}

Answer 1

Ah brilliant. That's worked! Thanks Saleh. After playing around with both our codes, mine seemed to work with the var declaration at the top and without NSMenuDelegate instance. My issue seems to be that I was saying :
let statusItem = NSStatusBar.system.statusItem(withLength: NSStatusItem.variableLength)
All I had to do to make it work was remove the 'let' and just say:
statusItem = NSStatusBar.system.statusItem(withLength: NSStatusItem.variableLength)

Answer 2

AppDelegate should be an instance of NSMenuDelegate
Define the statusItem at creation
Setup the button title in the applicationDidFinishLaunching callback
class AppDelegate: NSObject, NSApplicationDelegate, NSMenuDelegate {
let statusItem = NSStatusBar.system.statusItem(withLength:NSStatusItem.variableLength)
func applicationDidFinishLaunching(_ aNotification: Notification) {
if let button = statusItem.button {
//button.image = NSImage(named:NSImage.Name("StatusBarButtonImage"))
button.title = "connect"
//button.action = #selector(doSomething(_:))
}
}