如何在带有工具栏的窗口控制器上显示第二个视图？

import UIKit

class ToolbarViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // 创建工具栏
        let toolbar = UIToolbar(frame: CGRect(x: 0, y: 0, width: view.frame.width, height: 44))
        view.addSubview(toolbar)
        
        // 创建按钮
        let button = UIBarButtonItem(title: "显示第二个视图", style: .plain, target: self, action: #selector(showSecondView))
        toolbar.items = [button]
    }
    
    @objc func showSecondView() {
        // 创建第二个视图
        let secondView = SecondView(frame: CGRect(x: 0, y: 44, width: view.frame.width, height: view.frame.height - 44))
        view.addSubview(secondView)
    }
}

class FirstView: UIView {
    // 第一个视图的实现
}

class SecondView: UIView {
    // 第二个视图的实现
}