Update constraints swift layoutIfNeeded doesn't work - ios

Question

I need to update constraints (height of my CollectionView) when request is done and I have images from server, so height of View also will change.
Result screen
what I need screen
My code:
DispatchQueue.main.async {
self.cvActivity.alpha = 0
self.collectionView.reloadData()
self.collectionView.heightAnchor.constraint(equalToConstant: self.cellWidth * 2).isActive = true
self.collectionView.setNeedsUpdateConstraints()
self.collectionView.setNeedsLayout()
self.view.layoutIfNeeded()
}

Answer 1

Well, basic idea by #J. Doe is correct, here some code explanation (for simplicity i used UIView, not UICollectionView):
import UIKit
class ViewController: UIViewController {
#IBOutlet var heightConstraint: NSLayoutConstraint! // link the height constraint to your collectionView
private var height: CGFloat = 100 // you should keep constraint height for different view states somewhere
override func updateViewConstraints() {
heightConstraint.constant = height // set the correct height
super.updateViewConstraints()
}
// update height by button press with animation
#IBAction func increaseHight(_ sender: UIButton) {
height *= 2
UIView.animate(withDuration: 0.3) {
self.view.setNeedsUpdateConstraints()
self.view.layoutIfNeeded() // if you call `layoutIfNeeded` on your collectionView, animation doesn't work
}
}
}
Result:

Answer 2

Define a height for your collectionView, create an outlet from that constraint and increase the constant of that constraint and call layoutifneeded in an animation block

Answer 3

You need to make object of your Height constraint from storyboard
#IBOutlet weak var YourHeightConstraintName: NSLayoutConstraint!
YourConstraintName.constant = valueYouWantToGive
---------OR--------
collectionViewOutlet.view.frame = CGRect(x:
collectionViewOutlet.frame.origin.x , y:
collectionViewOutlet.frame.origin.y, width:
collectionViewOutlet.frame.width, height:
yourheightValue)