为什么这个 swift 代码不显示文本字段？

问：

代码应该只在窗口中查看“Hello， World！”。窗口随即出现，但文本未显示。为什么？

我可以看到偶数命令文本字段在前面查看。window.makeKeyAndOrderFront(nil)

错误：没有错误或警告

import Cocoa

@main
class AppDelegate: NSObject, NSApplicationDelegate {

    @IBOutlet var window: NSWindow!

    func applicationDidFinishLaunching(_ aNotification: Notification) {
        // Create a new window
        window = NSWindow(contentViewController: TextFieldViewController())
        // Make the window visible
        window.makeKeyAndOrderFront(nil)
    }

    func applicationWillTerminate(_ aNotification: Notification) {
        // Insert code here to tear down your application
    }

    func applicationSupportsSecureRestorableState(_ app: NSApplication) -> Bool {
        return true
    }
}

class TextFieldViewController: NSViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        // Create a label
        let label = NSTextField(labelWithString: "Hello, World!")
        label.frame = NSRect(x: 20, y: 100, width: 200, height: 20)
        // Add the label to the view
        view.addSubview(label)
    }
}