Update constraints swift layoutIfNeeded doesn't work

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)