尝试知道基于macOS Document的应用程序中的窗口何时关闭

问题在于window属性将始终在viewDidLoadMethod内部返回nil。您需要在viewWillAppear方法中设置委托：

class ViewController: NSViewController, NSWindowDelegate {    override func viewWillAppear() {        super.viewWillAppear()        view.window?.delegate = self    }    func windowWillClose(_ aNotification: Notification) {        print("windowWillClose")    }}