如何在Cocoa应用程序中切换视图？

import Cocoa

class ViewController: NSViewController {
    // 创建视图控制器
    let firstViewController = FirstViewController()
    let secondViewController = SecondViewController()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // 添加第一个子视图
        view.addSubview(firstViewController.view)
    }
    
    // 切换到第一个视图
    @IBAction func switchToFirstView(_ sender: Any) {
        // 移除第二个子视图
        secondViewController.view.removeFromSuperview()
        
        // 添加第一个子视图
        view.addSubview(firstViewController.view)
    }
    
    // 切换到第二个视图
    @IBAction func switchToSecondView(_ sender: Any) {
        // 移除第一个子视图
        firstViewController.view.removeFromSuperview()
        
        // 添加第二个子视图
        view.addSubview(secondViewController.view)
    }
}

class FirstViewController: NSViewController {
    override func loadView() {
        view = NSView(frame: NSRect(x: 0, y: 0, width: 200, height: 200))
        view.wantsLayer = true
        view.layer?.backgroundColor = NSColor.red.cgColor
    }
}

class SecondViewController: NSViewController {
    override func loadView() {
        view = NSView(frame: NSRect(x: 0, y: 0, width: 200, height: 200))
        view.wantsLayer = true
        view.layer?.backgroundColor = NSColor.blue.cgColor
    }
}