IOS Swift：当用户到达滚动底部时，如何扩展scrollview并执行新进程？

Question

我希望通过快速代码在我的照片显示应用中制作无限的Scrollview。 我可以找到像“scrollViewDidEndDragging：willDecelerate”这样的Object-c方法来启用它，但不能用于swift。这是我的代码，我尝试使用“scrollView.contentOffset.y”但不起作用。有人可以帮助实现这一目标吗？ 我还在故事板中创建了UIScrollView。

import UIKit

class ViewController: UIViewController {

@IBOutlet var scrollView: UIScrollView!

    scrollView.pagingEnabled = true
    scrollView.scrollEnabled = true
    scrollView.directionalLockEnabled = true
    scrollView.showsHorizontalScrollIndicator = false
    scrollView.showsVerticalScrollIndicator = true
    scrollView.bounces = true
    scrollView.scrollsToTop = false
    self.scrollView.contentSize = CGSizeMake(620, 480*3);
            self.navigationItem.titleView = pageControl

    let imgarray2 = ["1446420031.jpg", "4500129.jpg", 475323.jpg"]

    for (index, value) in enumerate(imgarray2) {
        var setx = 0
        var sety = index*480
        var imgnum = index+1
        let url = NSURL.URLWithString("\(value)");
        var err: NSError?
        var imageData :NSData = NSData.dataWithContentsOfURL(url,options: NSDataReadingOptions.DataReadingMappedIfSafe, error: &err)
        var blueimage = UIImage(data:imageData)
        var blueView = UIImageView(image: blueimage)
        blueView.contentMode = UIViewContentMode.ScaleAspectFill
        blueView.frame = CGRect(origin: CGPoint(x: setx, y: sety), size:blueimage.size)
        scrollView.addSubview(blueView)
    }

    if (scrollView.contentOffset.y >= (scrollView.contentSize.height - scrollView.frame.size.height)) {
        self.scrollView.contentSize = CGSizeMake(620, 480*6);
        for (index, value) in enumerate(imgarray2) {
            var setx = 0
            var sety = index*480+(480*3)
            var imgnum = index+1
            let url = NSURL.URLWithString("\(value)");
            var err: NSError?
            var imageData :NSData = NSData.dataWithContentsOfURL(url,options: NSDataReadingOptions.DataReadingMappedIfSafe, error: &err)
            var blueimage = UIImage(data:imageData)
            var blueView = UIImageView(image: blueimage)
            blueView.contentMode = UIViewContentMode.ScaleAspectFill
            blueView.frame = CGRect(origin: CGPoint(x: setx, y: sety), size:blueimage.size)
            scrollView.addSubview(blueView)
        }
    }