Populate in UIScrollView.

ScrollViewController.swift

//add all images to the list
  func setupList() {
    
    for i in herbs.indices {
      
      //create image view
      let imageView  = UIImageView(image: UIImage(named: herbs[i].image))
      imageView.tag = i
      imageView.contentMode = .scaleAspectFill
      imageView.isUserInteractionEnabled = true
      imageView.layer.cornerRadius = 20.0
      imageView.layer.masksToBounds = true
      listView.addSubview(imageView)
      
      //attach tap detector
      imageView.addGestureRecognizer(UITapGestureRecognizer(target: self, action: #selector(didTapImageView)))
    }
    
    listView.backgroundColor = UIColor.clear
    positionListItems()
  }
  
  //position all images inside the list
  func positionListItems() {
    let listHeight = listView.frame.height
    let itemHeight: CGFloat = listHeight * 1.33
    let aspectRatio = UIScreen.main.bounds.height / UIScreen.main.bounds.width
    let itemWidth: CGFloat = itemHeight / aspectRatio
    
    let horizontalPadding: CGFloat = 10.0
    
    for i in herbs.indices {
      let imageView = listView.viewWithTag(i) as! UIImageView
      imageView.frame = CGRect(
        x: CGFloat(i) * itemWidth + CGFloat(i+1) * horizontalPadding, y: 0.0,
        width: itemWidth, height: itemHeight)
    }
    
    listView.contentSize = CGSize(
      width: CGFloat(herbs.count) * (itemWidth + horizontalPadding) + horizontalPadding,
      height:  0)
  }
  
  //MARK: Actions
  
  func didTapImageView(_ tap: UITapGestureRecognizer) {
    selectedImage = tap.view as? UIImageView
    
    let index = tap.view!.tag
    let selectedHerb = herbs[index]
    
    //present details view controller
    let herbDetails = storyboard!.instantiateViewController(withIdentifier: "HerbDetailsViewController") as! HerbDetailsViewController
    herbDetails.herb = selectedHerb
    present(herbDetails, animated: true, completion: nil)
  }