Issue with Scroll View. Unexpectedly found nil while unwrapping optional value - ios

Question

I have a UIScrollView, and am using a UIPageControl to present images. The moment the first image appears, the program crashes and indicates a nil value was found.
EDIT: I'm no longer downloading images for the Scroll View, yet I'm still getting the error. The image appears and then the program crashes. Here is the stripped down code. Totally at a loss at this point. FYI, the reason I declare the variable i is I intend to loop and add additional images:
import UIKit
class HistoryViewController: UIViewController {
#IBOutlet weak var scrollView: UIScrollView!
var frame = CGRect(origin: CGPoint(x: 0,y :0), size: CGSize(width: 0, height: 0))
override func viewDidLoad() {
super.viewDidLoad()
self.scrollView.isPagingEnabled = true
let i = 0
frame.origin.x = self.scrollView.frame.size.width * CGFloat(i)
frame.size = self.scrollView.frame.size
let subView = UIImageView(frame: frame)
subView.image = UIImage(named: "maudite")
subView.contentMode = .scaleAspectFit
self.scrollView.addSubview(subView)
self.scrollView.contentSize = CGSize(width: self.scrollView.frame.size.width * CGFloat(1), height: self.scrollView.frame.size.height)
}
}
.....................
I have two theories why this is happening. The first is that The images for the subView that I add to the ScrollView haven't loaded yet. I'm using AlamoFireImage, which downloads images asynchronously.
This is the code that configures the Scroll View:
func configureScrollView() {
self.myScrollView.isPagingEnabled = true
for index in 0..<imageURLS.count {
frame.origin.x = self.myScrollView.frame.size.width * CGFloat(index)
frame.size = self.myScrollView.frame.size
let subView = UIImageView(frame: frame)
if let url = URL(string: imageURLS[index]) {
subView.af_setImage(withURL: (url))
subView.contentMode = .scaleAspectFit
self.myScrollView.addSubview(subView)
}
}
self.myScrollView.contentSize = CGSize(width: self.myScrollView.frame.size.width * CGFloat(imageURLS.count), height: self.myScrollView.frame.size.height)
pageControl.numberOfPages = imageURLS.count
}
The other thing that might be the cause of the issue is that I first have to download the image URL's. I do this and store them in an array. When that is complete, I call the configureScrollView(). I do the call on the Main Thread. Does the function then run on the Main Thread?
for dict in responseArray {
if let url = dict["fileName"] as? String {
let fullURL = "http://www.smarttapp.com" + url
print(fullURL)
self.imageURLS.append(fullURL)
}
}
DispatchQueue.main.async {
self.activityIndicator.stopAnimating()
self.activityIndicator.isHidden = true
self.networkingState = .finishedSearching
self.configureScrollView()
}
}