Difference between instantiating VC from storyboard vs. programatically - ios

Question

The comparison is between this:
let viewController = storyboard!.instantiateViewControllerWithIdentifier("ViewController") as! AViewController
versus this:
let viewController = AViewController()
Unfortunately, this question is not able to answer my question.
I've created this view controller:
final class ImageVC: UIViewController {
var imageView: UIImageView!
var scrollView: UIScrollView!
var originLabel: UILabel!
var image: UIImage?
override func viewDidLoad() {
super.viewDidLoad()
guard let image = image else { fatalError() }
imageView = UIImageView(image: image)
scrollView = UIScrollView(frame: view.bounds)
scrollView.autoresizingMask = [.FlexibleWidth, .FlexibleHeight]
scrollView.backgroundColor = UIColor.blackColor()
scrollView.contentSize = imageView.bounds.size
scrollView.addSubview(imageView)
view.addSubview(scrollView)
originLabel = UILabel(frame: CGRect(x: 20, y: 30, width: 0, height: 0))
originLabel.backgroundColor = UIColor.blackColor()
originLabel.textColor = UIColor.whiteColor()
view.addSubview(originLabel)
scrollView.delegate = self
setZoomParametersForSize(scrollView.bounds.size)
}
override func viewWillLayoutSubviews() {
print("layout")
setZoomParametersForSize(scrollView.bounds.size)
}
func setZoomParametersForSize(scrollViewSize: CGSize) {
let imageSize = imageView.bounds.size
let widthScale = scrollViewSize.width / imageSize.width
let heightScale = scrollViewSize.height / imageSize.height
let minScale = min(widthScale, heightScale)
scrollView.minimumZoomScale = minScale
scrollView.maximumZoomScale = 3.0
scrollView.zoomScale = minScale
}
}
extension ImageVC: UIScrollViewDelegate {
func viewForZoomingInScrollView(scrollView: UIScrollView) -> UIView? {
return imageView
}
func scrollViewDidScroll(scrollView: UIScrollView) {
originLabel.text = "\(scrollView.contentOffset)"
originLabel.sizeToFit()
}
}
This is meant to take an image, and when presented, will allow the user to zoom/pan through the image.
When I instantiate this VC using the first method (by instantiating from storyboard with identifier), it behaves fine.
However, when instantiating it the second way; let viewController = ImageVC(), viewWillLayoutSubviews will be triggered whenever scrollView detects movement, disallowing the ability to zoom in and out.
Advice appreciated.