如何在Swift4中以编程方式实现UIScrollView和UIPageControl？

import UIKit

class ViewController: UIViewController {
    var scrollView: UIScrollView!
    var pageControl: UIPageControl!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        // 添加UIScrollView
        scrollView = UIScrollView(frame: CGRect(x: 0, y: 0, width: view.frame.width, height: view.frame.height))
        scrollView.isPagingEnabled = true
        scrollView.delegate = self
        view.addSubview(scrollView)
        
        // 添加UIPageControl
        pageControl = UIPageControl(frame: CGRect(x: 0, y: view.frame.height - 50, width: view.frame.width, height: 50))
        pageControl.numberOfPages = 3
        pageControl.currentPage = 0
        pageControl.addTarget(self, action: #selector(pageControlValueChanged(_:)), for: .valueChanged)
        view.addSubview(pageControl)
        
        // 添加内容视图
        let contentViewWidth = view.frame.width * CGFloat(pageControl.numberOfPages)
        let contentView = UIView(frame: CGRect(x: 0, y: 0, width: contentViewWidth, height: view.frame.height))
        contentView.backgroundColor = UIColor.red
        scrollView.addSubview(contentView)
        
        // 设置UIScrollView的contentSize
        scrollView.contentSize = contentView.frame.size
    }
    
    @objc func pageControlValueChanged(_ sender: UIPageControl) {
        let xOffset = scrollView.frame.width * CGFloat(sender.currentPage)
        scrollView.setContentOffset(CGPoint(x: xOffset, y: 0), animated: true)
    }
}

extension ViewController: UIScrollViewDelegate {
    func scrollViewDidScroll(_ scrollView: UIScrollView) {
        let pageIndex = round(scrollView.contentOffset.x / scrollView.frame.width)
        pageControl.currentPage = Int(pageIndex)
    }
}