vertically align text in a CATextLayer?

Question

I am working on a CATextLayer that I want to use in both Mac and iOS. Can I control the vertical alignment of the text within the layer?

In this particular case, I

Answer 1

So there is no "direct" way of doing this but you can accomplish the same thing by using text metrics:

http://developer.apple.com/library/ios/#documentation/UIKit/Reference/NSString_UIKit_Additions/Reference/Reference.html

... for example, find the size of the text then use that information to place it where you want in the parent layer. Hope this helps.

Answer 2

I'd like to propose a solution that takes multiline wrapping inside the available box into account:

final class CACenteredTextLayer: CATextLayer {
    override func draw(in ctx: CGContext) {
        guard let attributedString = string as? NSAttributedString else { return }

        let height = self.bounds.size.height
        let boundingRect: CGRect = attributedString.boundingRect(
            with: CGSize(width: bounds.width,
                         height: CGFloat.greatestFiniteMagnitude),
            options: NSString.DrawingOptions.usesLineFragmentOrigin,
            context: nil)
        let yDiff: CGFloat = (height - boundingRect.size.height) / 2

        ctx.saveGState()
        ctx.translateBy(x: 0.0, y: yDiff)
        super.draw(in: ctx)
        ctx.restoreGState()
    }
}

Answer 3

Swift 5.3 for macOS

class VerticallyAlignedTextLayer : CATextLayer {
    /* Credit - purebreadd - 6/24/2020
        https://stackoverflow.com/questions/4765461/vertically-align-text-in-a-catextlayer
     */

    func calculateMaxLines() -> Int {
        let maxSize = CGSize(width: frame.size.width, height: frame.size.width)
        let font = NSFont(descriptor: self.font!.fontDescriptor, size: self.fontSize)
        let charSize = floor(font!.capHeight)
        let text = (self.string ?? "") as! NSString
        let textSize = text.boundingRect(with: maxSize, options: .usesLineFragmentOrigin, attributes: [NSAttributedString.Key.font: font!], context: nil)
        let linesRoundedUp = Int(floor(textSize.height/charSize))
        return linesRoundedUp
    }
        
    override func draw(in context: CGContext) {
        let height = self.bounds.size.height
        let fontSize = self.fontSize
        let lines = CGFloat(calculateMaxLines())
        let yDiff = -(height - lines * fontSize) / 2 - lines * fontSize / 6.5 // Use -(height  - lines * fontSize) / 2 - lines * fontSize / 6.5 when in non-flipped coordinates (like macOS's default)

        context.saveGState()
        context.translateBy(x: 0, y: yDiff)
        super.draw(in: context)
        context.restoreGState()
    }
}

Notice I am dividing fontSize by 6.5, which seems to work better for my application of this solution. Thanks @purebreadd!