This is my code:

import UIKit

class DocumentViewController: UIViewController, UIScrollViewDelegate {
    
    func viewForZooming(in scrollView: UIScrollView) -> UIView? {
        return scrollViewContainer
    }
    
    func scrollViewDidZoom(_ scrollView: UIScrollView) {
        let scrollViewSize = scrollView.bounds.size
        let scrollViewContainerSize = scrollViewContainer.frame.size
        let verticalPadding = scrollViewContainerSize.height < scrollViewSize.height ? (scrollViewSize.height - scrollViewContainerSize.height) / 2 : 0
        let horizontalPadding = scrollViewContainerSize.width < scrollViewSize.width ? (scrollViewSize.width - scrollViewContainerSize.width) / 2 : 0
        scrollView.contentInset = UIEdgeInsets(top: verticalPadding, left: horizontalPadding, bottom: verticalPadding, right: horizontalPadding)
    }
  
    let scrollView: UIScrollView = {
        let scrollView = UIScrollView()
        scrollView.translatesAutoresizingMaskIntoConstraints = false
        scrollView.minimumZoomScale = 0.1
        scrollView.maximumZoomScale = 4.0
        scrollView.zoomScale = 1.0
        return scrollView
    }()
  
    let scrollViewContainer: UIStackView = {
        let view = UIStackView()
        view.translatesAutoresizingMaskIntoConstraints = false
        view.axis = .vertical
        view.spacing = 15
        return view
    }()

    override func viewDidLoad() {
        super.viewDidLoad()
        scrollView.delegate = self
        view.backgroundColor = .gray
        view.addSubview(scrollView)
        scrollView.addSubview(scrollViewContainer)
        
        let uiview1 = UIView(frame: .zero)
        uiview1.heightAnchor.constraint(equalToConstant: 1000).isActive = true
        uiview1.widthAnchor.constraint(equalToConstant: 1000).isActive = true
        scrollViewContainer.addArrangedSubview(uiview1)
        uiview1.backgroundColor = .white
        
        let uiview2 = UIView(frame: .zero)
        uiview2.heightAnchor.constraint(equalToConstant: 1000).isActive = true
        uiview2.widthAnchor.constraint(equalToConstant: 1000).isActive = true
        scrollViewContainer.addArrangedSubview(uiview2)
        uiview2.backgroundColor = .white
        
        let uiview3 = UIView(frame: .zero)
        uiview3.heightAnchor.constraint(equalToConstant: 1000).isActive = true
        uiview3.widthAnchor.constraint(equalToConstant: 1000).isActive = true
        scrollViewContainer.addArrangedSubview(uiview3)
        uiview3.backgroundColor = .white
        
        let uiview4 = UIView(frame: .zero)
        uiview4.heightAnchor.constraint(equalToConstant: 1000).isActive = true
        uiview4.widthAnchor.constraint(equalToConstant: 1000).isActive = true
        scrollViewContainer.addArrangedSubview(uiview4)
        uiview4.backgroundColor = .white
        
        let uiview5 = UIView(frame: .zero)
        uiview5.heightAnchor.constraint(equalToConstant: 1000).isActive = true
        uiview5.widthAnchor.constraint(equalToConstant: 2000).isActive = true
        scrollViewContainer.addArrangedSubview(uiview5)
        uiview5.backgroundColor = .white
        
        showBounds()
        setConstraints()
    }
    
    func setConstraints() {
        scrollView.leadingAnchor.constraint(equalTo: view.leadingAnchor).isActive = true
        scrollView.trailingAnchor.constraint(equalTo: view.trailingAnchor).isActive = true
        scrollView.topAnchor.constraint(equalTo: view.topAnchor).isActive = true
        scrollView.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true
        scrollViewContainer.leadingAnchor.constraint(equalTo: scrollView.leadingAnchor).isActive = true
        scrollViewContainer.trailingAnchor.constraint(equalTo: scrollView.trailingAnchor).isActive = true
        scrollViewContainer.topAnchor.constraint(equalTo: scrollView.topAnchor).isActive = true
        scrollViewContainer.bottomAnchor.constraint(equalTo: scrollView.bottomAnchor).isActive = true
        
    }
        
    func showBounds() {
        view.layer.borderWidth = 5.0
        view.layer.borderColor = UIColor.blue.cgColor
        scrollViewContainer.layer.borderWidth = 5.0
        scrollViewContainer.layer.borderColor = UIColor.red.cgColor
        scrollView.layer.borderWidth = 3.0
        scrollView.layer.borderColor = UIColor.yellow.cgColor
    }

}

This code gives the following behaviour: https://i.stack.imgur.com/gNxnD.gif

You can see that whereas the last test UIView I made in viewDidLoad has a width of 2000, it ends up being cut off for some reason, as if its width is 1000. Additionally, if I change the width of the last view to 500, I get this behaviour.

So it seems that scrollViewContainer (?) is resizing to the smallest width out of those test UIViews. All I want is for it to allow different sized views, with the default width being the widest child view, as in this mockup.

CodePudding user response：

You need to add 'alignment' to your stack view. Please try this:

let scrollViewContainer: UIStackView = {
    let view = UIStackView()
    view.translatesAutoresizingMaskIntoConstraints = false
    view.axis = .vertical
    view.alignment = .center
    view.spacing = 15
    return view
}()