如何在启动Cocoa应用程序时显示启动画面？

import Cocoa

class AppDelegate: NSObject, NSApplicationDelegate {
    var splashWindow: NSWindow?
    var mainWindow: NSWindow?

    func applicationDidFinishLaunching(_ aNotification: Notification) {
        // 创建启动画面窗口
        let splashViewController = SplashViewController()
        let splashWindow = NSWindow(contentViewController: splashViewController)
        self.splashWindow = splashWindow

        // 设置启动画面窗口的样式和内容
        splashWindow.styleMask = .borderless
        splashWindow.backgroundColor = .clear
        splashWindow.level = .floating
        splashWindow.isOpaque = false
        splashWindow.center()

        // 显示启动画面窗口
        splashWindow.makeKeyAndOrderFront(nil)

        // 创建主窗口
        let mainViewController = MainViewController()
        let mainWindow = NSWindow(contentViewController: mainViewController)
        self.mainWindow = mainWindow

        // 在主窗口加载完成后，隐藏启动画面窗口
        mainWindow.delegate = self
    }
}

extension AppDelegate: NSWindowDelegate {
    func windowDidLoad(_ notification: Notification) {
        // 隐藏启动画面窗口
        splashWindow?.orderOut(nil)

        // 显示主窗口
        mainWindow?.center()
        mainWindow?.makeKeyAndOrderFront(nil)
    }
}