iOS 10.3: NSStrikethroughStyleAttributeName is not rendered if applied to a sub range of NSMutableAttributedString

Question

A strikethrough (single, double, ...) added as attribute to an instance of NSMutableAttributedString is not rendered if the apply range is not the whole string range.

This happens using addAttribute(_ name: String, value: Any, range: NSRange), insert(_ attrString: NSAttributedString, at loc: Int), append(_ attrString: NSAttributedString), ...

Broken by Apple in early iOS 10.3 betas, and not fixed in 10.3 final.

Credit: https://openradar.appspot.com/31034683

Answer 1

Setting the baseline offset seems to fix it:

[attributedStr addAttribute:NSBaselineOffsetAttributeName value:@0 range:NSMakeRange(0, 10)];
[attributedStr addAttribute:NSStrikethroughStyleAttributeName value:@2 range:NSMakeRange(0, 10)];

This is a known bug in iOS 10.3

Answer 2

Adding a NSBaselineOffsetAttributeName, as explained here, to the attributed string brings back the strikethrough line. Overriding drawText:in: can be slow especially on Collection View or Table View Cells.

Answer 3

Found a workaround for our specific scenario (we don't specify any styling with UILabel's properties, but all with NSAttributedString attributes):

/// This UILabel subclass accomodates conditional fix for NSAttributedString rendering broken by Apple in iOS 10.3
final class PriceLabel: UILabel {

    override func drawText(in rect: CGRect) {
        guard let attributedText = attributedText else {
            super.drawText(in: rect)
            return
        }

        if #available(iOS 10.3, *) {
            attributedText.draw(in: rect)
        } else {
            super.drawText(in: rect)
        }
    }
}

NOTE: if you mix UILabel's styling properties with NSAttributedString attributes, you should think of creating a new attributed string before rendering, apply UILabel's styling on it and then re-apply all attributedText's attributes over it.