Animate subview AutoLayout constraint changes - ios

Question

Numerous tutorials on animating AutoLayout constraints suggest to update constant property of a constraint and then call layoutIfNeeded() in animation block.
My situation is a bit tricky.
I have a view that houses 3 subviews. The height of this superview is not fixed - it is calculated as a sum of heights of its subviews.
On some event, I ask one of those 3 subviews to toggle its height (it changes between 0 and 30, i.e. I want to smoothly hide and show it).
The code is similar to this:
// In superview
subview1.isVisibleInContext = !subview1.isVisibleInContext
// In subview
class MySubview: UIView {
#IBOutlet var heightConstraint: NSLayoutConstraint!
var isVisibleInContext = false {
didSet {
updateHeight()
}
}
func toggleHeight() {
let newHeight = isVisibleInContext ? 30 : 0
layoutIfNeeded()
heightConstraint.constant = newHeight
UIView.animate(withDuration: 0.8) {
self.layoutIfNeeded()
}
}
}
Unfortunately, this does not work as I expect.
I can see the smooth change of the height of my subview, but the height of my superview is recalculated immediately after I set the new value for my subview height constraint.
I want to see the height of the superview gradually increasing/decreasing as on of its subviews grows or decreases.
Please someone point me in the right direction. Any help is appreciated.
Thanks a lot!

Answer 1

The animation block should be in the UIView that contains the 3 MySubviews. Inside the MySubview class you only update the height constraint's constant:
In Subview
func toggleHeight() {
let newHeight = isVisibleInContext ? 30 : 0
heightConstraint.constant = newHeight
}
Then in the UIView that contains the 3 MySubviews you animate the change:
In Superview
func toggleHeight(with subview: MySubview) {
subview.toggleHeight()
UIView.animate(withDuration: 0.8) {
self.view.layoutIfNeeded()
}
}

Answer 2

The first thing, that was incorrect in my approach was executing self.layoutIfNeeded(). Having investigated the issue I learned out that I had to execute it on the superivew, like this:
self.superview?.layoutIfNeeded()
That also didn't work out for a reason. The main issue in this case was that the view, which had 3 subviews inside was itself a subview of view. So to make it work I had to use the following code:
self.superview?.superview?.layoutIfNeeded()
Definitely not good that subview has to know the hierarchy of views, however it works.