Dynamic UICollectionView header size based on UILabel

Question

I\'ve read a bunch of posts on adding header to UICollectionView. In an iOS 7+ app in Swift, I\'m trying to add a header with a UILabel in it whose height should adjust base

Answer 1

Like the questioner, I had a UICollectionView that contained a header with a single label, whose height I wanted to vary. I created an extension to UILabel to measure the height of a multiline label with a known width:

public extension UILabel {
    public class func size(withText text: String, forWidth width: CGFloat) -> CGSize {
        let measurementLabel = UILabel()
        measurementLabel.text = text
        measurementLabel.numberOfLines = 0
        measurementLabel.lineBreakMode = .byWordWrapping
        measurementLabel.translatesAutoresizingMaskIntoConstraints = false
        measurementLabel.widthAnchor.constraint(equalToConstant: width).isActive = true
        let size = measurementLabel.systemLayoutSizeFitting(UILayoutFittingCompressedSize)
        return size
    }
}

Note: the above is in Swift 3 syntax.

Then I implement the header size method of UICollectionViewDelegateFlowLayout as:

extension MyCollectionViewController : UICollectionViewDelegateFlowLayout {
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, referenceSizeForHeaderInSection section: Int) -> CGSize {
        let text = textForHeader(inSection: section)
        var size =  UILabel.size(withAttributedText: text, forWidth: collectionView.frame.size.width)
        size.height = size.height + 16
        return size
    }
}

The work of calculating the header size is delegated to the above UILabel extension. The +16 is a experimentally derived fixed offset (8 + 8) that is based on margins and could be obtained programmatically.

All that's needed in the header callback is just to set the text:

override func collectionView(_ collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, at indexPath: IndexPath) -> UICollectionReusableView {
    if kind == UICollectionElementKindSectionHeader, let headerView = collectionView.dequeueReusableSupplementaryView(ofKind: kind, withReuseIdentifier: headerIdentifier, for: indexPath) as?  MyCollectionHeader {
        let text = textForHeader(inSection: section)
        headerView.label.text = text
        return headerView
    }
    return UICollectionReusableView()
}