如何在ModalView中添加多个按钮到ScrollView？

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        
        // 创建一个ModalView
        let modalView = UIView(frame: CGRect(x: 0, y: 0, width: 300, height: 400))
        modalView.backgroundColor = .white
        
        // 创建一个ScrollView
        let scrollView = UIScrollView(frame: CGRect(x: 0, y: 0, width: 300, height: 400))
        
        // 添加按钮到ScrollView
        let button1 = UIButton(frame: CGRect(x: 20, y: 20, width: 100, height: 40))
        button1.setTitle("按钮1", for: .normal)
        button1.addTarget(self, action: #selector(button1Tapped), for: .touchUpInside)
        scrollView.addSubview(button1)
        
        let button2 = UIButton(frame: CGRect(x: 20, y: 80, width: 100, height: 40))
        button2.setTitle("按钮2", for: .normal)
        button2.addTarget(self, action: #selector(button2Tapped), for: .touchUpInside)
        scrollView.addSubview(button2)
        
        let button3 = UIButton(frame: CGRect(x: 20, y: 140, width: 100, height: 40))
        button3.setTitle("按钮3", for: .normal)
        button3.addTarget(self, action: #selector(button3Tapped), for: .touchUpInside)
        scrollView.addSubview(button3)
        
        // 设置ScrollView的contentSize
        scrollView.contentSize = CGSize(width: 300, height: 200)
        
        // 将ScrollView添加到ModalView中
        modalView.addSubview(scrollView)
        
        // 显示ModalView
        self.view.addSubview(modalView)
    }
    
    @objc func button1Tapped() {
        // 按钮1的点击事件处理
    }
    
    @objc func button2Tapped() {
        // 按钮2的点击事件处理
    }
    
    @objc func button3Tapped() {
        // 按钮3的点击事件处理
    }
}