-systemLayoutSizeFittingSize: returning incorrect height for tableHeaderView under iOS 8

Question

There are numerous threads about correctly sizing a tableHeaderView with auto-layout (one such thread) but they tend to pre-date iOS 8.

I have a situation with numerous

Answer 1

If the header just contains a single label then I use a UILabel extension to find a multiline label height given a 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.

With the size calculated above you can return the correct height in the UITableViewDelegate method:

func tableView(tableView: UITableView, heightForHeaderInSection section: Int) -> CGFloat