I'm implementing a custom NSToolbarItem that has a button and a dropdown, like Mail. The only thing that's not working, though, is that the NSMenuItem is disabled. Whatever I do, I can't get it enabled. Any idea what I'm doing wrong here?
class DropdownTypeToolbarItem: NSToolbarItem {
    private var handler: ((NSNumber) -> Void)?
    init(itemIdentifier: NSToolbarItem.Identifier, handler: ((NSNumber) -> Void)?) {
        super.init(itemIdentifier: itemIdentifier)
        self.handler = handler
        let control = NSSegmentedControl(labels: ["Open", ""],
                                         trackingMode: .momentary,
                                         target: self,
                                         action: #selector(open))
        let menu = NSMenu(title: "")
        menu.addItem(withTitle: "Export", action: #selector(export(_:)), keyEquivalent: "")
        control.setMenu(menu, forSegment: 1)
        control.setShowsMenuIndicator(true, forSegment: 1)
        self.view = control
    }
    @objc func open() {
        print("select open")
        self.handler?(0)
    }
    @objc func export(_ sender: Any) {
        print("select export")
        self.handler?(1)
    }
}