UIView animating its own height - ios

Question

I have made a simple example of a UIView inside a UIViewController, so that when I tap on the inner view, it increases and decreases its height. That works fine, but I can't make the height transition animate.
Here is the view controller, followed by the view:
class ViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
let theView = MyView()
theView.translatesAutoresizingMaskIntoConstraints = false
self.view.addSubview(theView)
NSLayoutConstraint.activate([
theView.topAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.topAnchor, constant: 50.0),
theView.leadingAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.leadingAnchor, constant:0.0),
theView.trailingAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.trailingAnchor, constant: 0.0),
theView.heightAnchor.constraint(equalToConstant: 925)
])
}
}
class MyView: UIView {
fileprivate var closedChanger = NSLayoutConstraint()
fileprivate var isOpen = false
init() {
super.init(frame: CGRect.zero)
setupView()
}
fileprivate func setupView() {
self.backgroundColor = .gray
self.translatesAutoresizingMaskIntoConstraints = true
closedChanger = self.heightAnchor.constraint(equalToConstant: 150.0)
NSLayoutConstraint.activate([
closedChanger // start off with it shorter
])
self.addGestureRecognizer(UITapGestureRecognizer(target: self, action: #selector(handleTap(sender:))))
}
#objc func handleTap(sender: UITapGestureRecognizer) {
UIView.animate(withDuration: 1.0, animations: {
self.closedChanger.constant = self.isOpen ? self.closedChanger.constant - 25 : self.closedChanger.constant + 25
// self.layoutIfNeeded()
})
isOpen.toggle()
}
}
The layoutIfNeeded doesn't affect it. Is a UIView not allowed to animate its own height change?

Answer 1

Your are kind of right when you say that a view can't animate itself. The problem is that you need to animate the change to the containing view, since that the is the view hierarchy that is changing.
You need to make the change to the constraint outside of the animation block, and then call layoutIfNeeded on the superview in the animation block.
#objc func handleTap(sender: UITapGestureRecognizer) {
self.closedChanger.constant = self.isOpen ? self.closedChanger.constant - 25 : self.closedChanger.constant + 25
UIView.animate(withDuration: 1.0, animations: {
self.superview?.layoutIfNeeded()
})
isOpen.toggle()
}