如何使用swift使用页面控件创建滚动视图？

import UIKit

class DummyVC: UIViewController, UIScrollViewDelegate {    let scrollView = UIScrollView(frame: CGRect(x:0, y:0, width:320,height: 300))    var colors:[UIColor] = [UIColor.red, UIColor.blue, UIColor.green, UIColor.yellow]    var frame: CGRect = CGRect(x:0, y:0, width:0, height:0)    var pageControl : UIPageControl = UIPageControl(frame: CGRect(x:50,y: 300, width:200, height:50))    override func viewDidLoad() {        super.viewDidLoad()        configurePageControl()        scrollView.delegate = self        scrollView.isPagingEnabled = true        self.view.addSubview(scrollView)        for index in 0..<4 { frame.origin.x = self.scrollView.frame.size.width * CGFloat(index) frame.size = self.scrollView.frame.size let subView = UIView(frame: frame) subView.backgroundColor = colors[index] self.scrollView .addSubview(subView)        }        self.scrollView.contentSize = CGSize(width:self.scrollView.frame.size.width * 4,height: self.scrollView.frame.size.height)        pageControl.addTarget(self, action: #selector(self.changePage(sender:)), for: UIControlEvents.valueChanged)    }    func configurePageControl() {        // The total number of pages that are available is based on how many available colors we have.        self.pageControl.numberOfPages = colors.count        self.pageControl.currentPage = 0        self.pageControl.tintColor = UIColor.red        self.pageControl.pageIndicatorTintColor = UIColor.black        self.pageControl.currentPageIndicatorTintColor = UIColor.green        self.view.addSubview(pageControl)    }    // MARK : TO CHANGE WHILE CLICKING ON PAGE ConTROL    func changePage(sender: AnyObject) -> () {        let x = CGFloat(pageControl.currentPage) * scrollView.frame.size.width        scrollView.setContentOffset(CGPoint(x:x, y:0), animated: true)    }    func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {        let pageNumber = round(scrollView.contentOffset.x / scrollView.frame.size.width)        pageControl.currentPage = Int(pageNumber)    }}