Using another scroll view to scroll tableview, cells aren't loading - ios

Question

I have a weird requirement for UI, and need to scroll a table view in a page view using the scroll view I embed the page view in. For example:
import UIKit
class TableVC: UIViewController {
let tableView = UITableView()
var observer: NSKeyValueObservation?
override func viewDidLoad() {
super.viewDidLoad()
setupTableView()
}
func setupTableView() {
view.addSubview(tableView)
tableView.translatesAutoresizingMaskIntoConstraints = false
NSLayoutConstraint.activate([
tableView.leadingAnchor.constraint(equalTo: view.leadingAnchor),
tableView.trailingAnchor.constraint(equalTo: view.trailingAnchor),
tableView.topAnchor.constraint(equalTo: view.topAnchor),
tableView.heightAnchor.constraint(equalToConstant: 2000)
])
tableView.dataSource = self
tableView.delegate = self
tableView.isScrollEnabled = false
tableView.backgroundColor = .blue
let handler = { (tableView: UITableView, change: NSKeyValueObservedChange<CGSize>) in
if let contentSize = change.newValue {
print("contentSize:", contentSize)
}
}
observer = tableView.observe(\UITableView.contentSize, options: [NSKeyValueObservingOptions.new], changeHandler: handler)
}
}
extension TableVC: UITableViewDelegate {
func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
50.0
}
}
extension TableVC: UITableViewDataSource {
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return 40
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = UITableViewCell()
cell.backgroundColor = .green
return cell
}
}
And the main view controller:
import UIKit
class ViewController: UIViewController {
private enum Constants {
static let pageViewControllerOptions: [UIPageViewController.OptionsKey: Any] = [
.interPageSpacing: CGFloat(8.0)
]
}
private let pageVC: UIPageViewController = UIPageViewController(
transitionStyle: .scroll,
navigationOrientation: .horizontal,
options: Constants.pageViewControllerOptions
)
let scrollView: UIScrollView = UIScrollView()
override func viewDidLoad() {
super.viewDidLoad()
view.addSubview(scrollView)
scrollView.pin(to: view)
let stackView = UIStackView()
stackView.axis = .vertical
stackView.frame = view.bounds
stackView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
scrollView.addSubview(stackView)
let blueView = UIView()
blueView.backgroundColor = .blue
stackView.addArrangedSubview(blueView)
blueView.translatesAutoresizingMaskIntoConstraints = false
blueView.heightAnchor.constraint(equalToConstant: 100.0).isActive = true
addChild(pageVC)
pageVC.didMove(toParent: self)
let pageView = pageVC.view!
stackView.addArrangedSubview(pageView)
pageVC.setViewControllers([TableVC()], direction: .forward, animated: false, completion: nil)
// 50 height with 20 cells works fine
// 50 height with 40 cells won't work beacuse it doesn't seem to load them all
scrollView.contentSize = CGSize(width: view.bounds.width, height: 2000 + 100)
}
}
With 40 cells I am expecting a content size of 2000, I set this above (allowing for the height of the blue view also). The scrolling works but it seems like at some point it has stopped generating the cells:
In the gif above you can see there are less than 40 cells. I have tried using a larger table view height, calling layoutIfNeeded but the result is the same. Is there anything I can do to fix this? I imagine the cells are not loading because I am not using the table view's own scroll view so cellForRow isn't triggered. Is there another way to load the cells?