UIStackView won't animate when changing the hidden property on iOS 9 - ios

Question

I am using a Stack view to create a kind of table UI, I have 6 views in a StackView 0,2,4 are visible and 1,3,5 are hidden. When tapping one of the visible views I wish to "open" one of the views that are hidden.
I have this code that works great on iOS 10 but from some reason I can not understand it is not working well on iOS 9.
Note that if I load the views all open, the close animation will work but it won't open when setting the hidden property to false.
Here is my code -
EDIT
After some debugging looks like the view height constraint is nor recovering from the hiding, and it's frame is still height is 0.
import UIKit
class DeckView: UIView {
}
class ViewController: UIViewController {
var scrollView: UIScrollView!
var stackView: UIStackView!
override func viewDidLoad() {
super.viewDidLoad()
scrollView = UIScrollView()
scrollView.translatesAutoresizingMaskIntoConstraints = false
view.addSubview(scrollView)
view.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "H:|[scrollView]|", options: .alignAllCenterX, metrics: nil, views: ["scrollView": scrollView]))
view.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "V:|[scrollView]|", options: .alignAllCenterX, metrics: nil, views: ["scrollView": scrollView]))
stackView = UIStackView()
stackView.translatesAutoresizingMaskIntoConstraints = false
stackView.spacing = 0
stackView.alignment = .center
stackView.distribution = .fillProportionally
stackView.axis = .vertical
scrollView.addSubview(stackView)
scrollView.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "H:|[stackView]|", options: NSLayoutFormatOptions.alignAllCenterX, metrics: nil, views: ["stackView": stackView]))
scrollView.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "V:|[stackView]|", options: NSLayoutFormatOptions.alignAllCenterX, metrics: nil, views: ["stackView": stackView]))
for i in 0 ..< 8 {
let view = DeckView()
view.tag = i
view.translatesAutoresizingMaskIntoConstraints = false
view.widthAnchor.constraint(equalToConstant: UIScreen.main.bounds.width).isActive = true
view.isUserInteractionEnabled = true
if i%2 == 0 {
view.backgroundColor = UIColor.magenta
let constriant = view.heightAnchor.constraint(equalToConstant:160)
constriant.priority = 999
view.addGestureRecognizer(UITapGestureRecognizer(target: self, action: #selector(self.openDeck(_:))))
view.addConstraint(constriant)
} else {
view.backgroundColor = UIColor.red
let constriant = view.heightAnchor.constraint(equalToConstant:160)
constriant.priority = 999
view.addConstraint(constriant)
view.isHidden = false
}
stackView.addArrangedSubview(view)
}
}
func openDeck(_ sender:UIGestureRecognizer) {
if let view = sender.view as? DeckView,
let childView = stackView.viewWithTag(view.tag + 1) {
UIView.animate(withDuration: 0.4, animations: {
childView.isHidden = !childView.isHidden
})
}
}
}

Answer 1

keep the view's height priority lower than 1000(go for 999).
Do not set setHidden:true if it is already hidden(This is UIStackView's bug)

Answer 2

If any one stumble on this issue.
I was able to solve this issue by removing the -
stackView.distribution = .fillProportionally
I am not sure why this happened but I found that Autolayout added a height constraint named 'UISV-fill-proportionally' with a constant of 0 and greater priority then my height constraint. removing the fillProportionally fixed the issue.