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When adjusting a label's text for self seizing collectionView cells I use the following function in sizeForItem:

func estimatedLabelHeight(text: String, width: CGFloat, font: UIFont) -> CGFloat 
 let size = CGSize(width: width, height: 1000)
 let options = NSStringDrawingOptions.usesFontLeading.union(.usesLineFragmentOrigin)
 let attributes = [NSAttributedStringKey.font: font]
 let rectangleHeight = String(text).boundingRect(with: size, options: options, attributes: attributes, context: nil).height
 return rectangleHeight

The function works fine and my cells expand accordingly.

What has happened though is there are several line breaks inside some of the text from the pricesLabel that get fed into the function. The line breaks are too "tight" so I followed this answer when creating my label to expand the spacing in between the line breaks.

let attributedString = NSMutableAttributedString(string: pricesText)
let paragraphStyle = NSMutableParagraphStyle()
paragraphStyle.lineSpacing = 7 // if I set this at 2 I have no problems
attributedString.addAttribute(.paragraphStyle, value: paragraphStyle, range: NSMakeRange(0, attributedString.length))

The problem is the text from pricesLabel inside the cell expands to far downwards. Using paragraphStyle.lineSpacing = 7 creates the space I want but it causes problems. If I set this to paragraphStyle.lineSpacing = 2 have no problems but the spacing is to tight.

As you can see in the picture the cell sizes the way it's supposed to but the the line break spacing in between the $8.00 and $12.00 makes the text expand to far and the text of $20.00 from the computedTotalLabel gets obscured.

I called sizeToFit() in layoutSubViews() but it made no difference:

override func layoutSubviews() 
 super.layoutSubviews()

 pricesLabel.sizeToFit()
 computedTotalLabel.sizeToFit()

How can I make the pricesLabel text adjusted with the line breaks size itself accordingly

class MyCell: UICollectionViewCell 

 let pricesLabel: UILabel = 
 let label = UILabel()
 label.translatesAutoresizingMaskIntoConstraints = false
 label.textAlignment = .right
 label.sizeToFit()
 label.font = UIFont.systemFont(ofSize: 15.5)
 label.adjustsFontSizeToFitWidth = true
 label.minimumScaleFactor = 0.5
 label.numberOfLines = 0
 label.sizeToFit()
 return label
 ()

 let computedTotalLabel: UILabel = 
 let label = UILabel()
 label.translatesAutoresizingMaskIntoConstraints = false
 label.textAlignment = .right
 label.textColor = .black
 label.sizeToFit()
 label.font = UIFont.boldSystemFont(ofSize: 15.5)
 label.adjustsFontSizeToFitWidth = true
 label.minimumScaleFactor = 0.5
 label.numberOfLines = 1
 label.sizeToFit()
 return label
 ()

 let staticTotalLabel: UILabel = 
 let label = UILabel()
 label.translatesAutoresizingMaskIntoConstraints = false
 label.text = "Total"
 label.textAlignment = .left
 label.textColor = .black
 label.font = UIFont.boldSystemFont(ofSize: 15.5)
 label.adjustsFontSizeToFitWidth = true
 label.minimumScaleFactor = 0.5
 label.numberOfLines = 1
 label.sizeToFit()
 return label
 ()

 let separatorLine: UIView = 
 let view = UIView()
 view.translatesAutoresizingMaskIntoConstraints = false
 view.backgroundColor = .lightGray
 return view
 ()

 override func layoutSubviews() 
 super.layoutSubviews()

 pricesLabel.sizeToFit()
 computedTotalLabel.sizeToFit()
 

 var myObject: MyObject? 
 didSet 

 // text is "$8.00n$12.00n"
 let pricesText = myObject?.myText ?? "error"

 let attributedString = NSMutableAttributedString(string: pricesText, attributes: [NSAttributedStringKey.font: UIFont.systemFont(ofSize: 15.5)])
 let paragraphStyle = NSMutableParagraphStyle()
 paragraphStyle.lineSpacing = 7
 attributedString.addAttribute(.paragraphStyle, value: paragraphStyle, range: NSMakeRange(0, attributedString.length))

 pricesLabel.attributedText = attributedString

 computedTotalLabel.text = functionThatTalliesUpAllThePrices(pricesText)

 configureAnchors()
 
 

 func configureAnchors() 

 addSubview(pricesLabel)
 addSubview(totalLabel)
 addSubview(staticTotalLabel) // this is the label on the left side of the pic that says Total:
 addSubview(separatorLine)

 pricesLabel.topAnchor.constraint(equalTo: self.topAnchor, constant: 12).isActive = true
 pricesLabel.rightAnchor.constraint(equalTo: self.rightAnchor, constant: -10).isActive = true

 staticTotalLabel.lastBaselineAnchor.constraint(equalTo: totalLabel.lastBaselineAnchor).isActive = true
 staticTotalLabel.leftAnchor.constraint(equalTo: self.leftAnchor, constant: 10).isActive = true
 staticTotalLabel.rightAnchor.constraint(equalTo: totalLabel.leftAnchor, constant: -10).isActive = true

 computedTotalLabel.topAnchor.constraint(equalTo: pricesLabel.bottomAnchor, constant: 0).isActive = true
 computedTotalLabel.rightAnchor.constraint(equalTo: self.rightAnchor, constant: -10).isActive = true

 separatorLine.topAnchor.constraint(equalTo: computedTotalLabel.bottomAnchor, constant: 12).isActive = true
 separatorLine.leftAnchor.constraint(equalTo: self.leftAnchor, constant: 10).isActive = true
 separatorLine.rightAnchor.constraint(equalTo: self.rightAnchor, constant: -10).isActive = true
 separatorLine.bottomAnchor.constraint(equalTo: self.bottomAnchor).isActive = true
 separatorLine.heightAnchor.constraint(equalToConstant: 1).isActive = true
 

This is the sizeForItem inside the collectionView cell. Not sure if this makes a difference to the problem so I added it anyway

class MyClass: UIViewController 

 let tableData = [MyObect]()

 func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize 

 let myObect = tableData[indexPath.item]

 // text is "$8.00n$12.00n"
 let pricesText = myObject?.myText ?? "error"

 let width = collectionView.frame.width

 let pricesLabelHeight = estimatedLabelHeight(text: pricesText, width: width, font: UIFont.systemFont(ofSize: 15.5))

 let total = functionThatTalliesUpAllThePrices(pricesText)
 let totalLabelHeight = estimatedLabelHeight(text: functionThatAddsUp, width: width, font: UIFont.boldSystemFont(ofSize: 15.5))

 // the 12 + 0 + 12 + 1 are the constant sizes I use inside the cell's configureAnchors functions
 let cellHeight = 12 + pricesLabelHeight + 0 + totalLabelHeight + 12 + 1

 return CGSize(width: width, height: ceil(cellHeight))
 

1st. I had to place the same estimatedLabelHeight(text: String, width: CGFloat, font: UIFont) inside the collectionView cell itself.

2nd. Inside the configureAnchors functions at the bottom of it I call pricesLabel.sizeToFit() and pricesLabel.layoutSubviews() and then I call the above function from step 1 to get the height of the pricesLabel from it's text.

3rd. I set the pricesLabel.heightAnchor.constraint(equalToConstant:) to the the height returned from step 2.

class MyCell: UICollectionViewCell 

 // step 1. place this function inside the collectionView cell
 func estimatedLabelHeight(text: String, width: CGFloat, font: UIFont) -> CGFloat 

 let size = CGSize(width: width, height: 1000)

 let options = NSStringDrawingOptions.usesFontLeading.union([.usesLineFragmentOrigin, .usesFontLeading])

 let attributes = [NSAttributedStringKey.font: font]

 let rectangleHeight = String(text).boundingRect(with: size, options: options, attributes: attributes, context: nil).height

 return rectangleHeight
 

 func configureAnchors() 

 // all the other anchors are here

 pricesLabel.sizeToFit()
 computedTotalLabel.sizeToFit()

 computedTotalLabel.layoutIfNeeded()
 pricesLabel.layoutIfNeeded()

 let pricesLabelText = pricesLabel.text ?? "error"

 let width = self.frame.width

 // step 2.
 let pricesLabelHeight = estimatedLabelHeight(text: pricesLabelText, width: width, font: UIFont.systemFont(ofSize: 15.5))

 // step 3.
 pricesLabel.heightAnchor.constraint(equalToConstant: pricesLabelHeight).isActive = true