Core Text - NSAttributedString line height done right?

Question

I\'m completely in the dark with Core Text\'s line spacing. I\'m using NSAttributedString and I specify the following attributes on it: - kCTFontAttributeName - kCTParagraph

Answer 1

This worked for me in Xcode 7.2. iOS 9.2.1. (Swift 2.1.):

  dispatch_async(dispatch_get_main_queue()) { () -> Void in
        let paragraphStyleWithSpacing           = NSMutableParagraphStyle()
        paragraphStyleWithSpacing.lineSpacing   = 2.0 //CGFloat
        let textWithLineSpacing                 = NSAttributedString(string: str, attributes: [NSParagraphStyleAttributeName : paragraphStyleWithSpacing])
        self.MY_TEXT_VIEW_NAME.attributedText   = textWithLineSpacing
    }

Answer 2

Swift 4 & 5

extension NSAttributedString {

    /// Returns a new instance of NSAttributedString with same contents and attributes with line spacing added.
     /// - Parameter spacing: value for spacing you want to assign to the text.
     /// - Returns: a new instance of NSAttributedString with given line spacing.
     func withLineSpacing(_ spacing: CGFloat) -> NSAttributedString {
         let attributedString = NSMutableAttributedString(attributedString: self)
         let paragraphStyle = NSMutableParagraphStyle()
         paragraphStyle.lineBreakMode = .byTruncatingTail
         paragraphStyle.lineSpacing = spacing
         attributedString.addAttribute(.paragraphStyle,
                                       value: paragraphStyle,
                                       range: NSRange(location: 0, length: string.count))
         return NSAttributedString(attributedString: attributedString)
     }
}

Answer 3

I tried all these answers, but to really get the EXACT line height that usually comes in design files from Sketch or Zeplin then you need to:

let ps = NSMutableParagraphStyle()
ps.minimumLineHeight = 34
ps.maximumLineHeight = 34
let attrText = NSAttributedString(
    string: "Your long multiline text that will have exact line height spacing",
    attributes: [
        .paragraphStyle: ps
    ]
)
someLabel.attributedText = attrText
someLabel.numberOfLines = 2
...

Answer 4

You can set/update line spacing and line height multiple from storyboard as well as programatically.

From Interface Builder:

Programmatically:

SWift 4

extension UILabel {

    // Pass value for any one of both parameters and see result
    func setLineSpacing(lineSpacing: CGFloat = 0.0, lineHeightMultiple: CGFloat = 0.0) {

        guard let labelText = self.text else { return }

        let paragraphStyle = NSMutableParagraphStyle()
        paragraphStyle.lineSpacing = lineSpacing
        paragraphStyle.lineHeightMultiple = lineHeightMultiple

        let attributedString:NSMutableAttributedString
        if let labelattributedText = self.attributedText {
            attributedString = NSMutableAttributedString(attributedString: labelattributedText)
        } else {
            attributedString = NSMutableAttributedString(string: labelText)
        }

        // Line spacing attribute

// Swift 4.2++


attributedString.addAttribute(NSAttributedString.Key.paragraphStyle, value:paragraphStyle, range:NSMakeRange(0, attributedString.length))

// Swift 4.1--
attributedString.addAttribute(NSAttributedStringKey.paragraphStyle, value:paragraphStyle, range:NSMakeRange(0, attributedString.length))

        self.attributedText = attributedString
    }
}

Now call extension function

let label = UILabel()
let stringValue = "How to\ncontrol\nthe\nline spacing\nin UILabel"

// Pass value for any one argument - lineSpacing or lineHeightMultiple
label.setLineSpacing(lineSpacing: 2.0) .  // try values 1.0 to 5.0

// or try lineHeightMultiple
//label.setLineSpacing(lineHeightMultiple = 2.0) // try values 0.5 to 2.0

Or using label instance (Just copy & execute this code to see result)

let label = UILabel()
let stringValue = "How to\ncontrol\nthe\nline spacing\nin UILabel"
let attrString = NSMutableAttributedString(string: stringValue)
var style = NSMutableParagraphStyle()
style.lineSpacing = 24 // change line spacing between paragraph like 36 or 48
style.minimumLineHeight = 20 // change line spacing between each line like 30 or 40

// Swift 4.2++
// Line spacing attribute
attrString.addAttribute(NSAttributedString.Key.paragraphStyle, value: style, range: NSRange(location: 0, length: stringValue.characters.count))

// Character spacing attribute
attrString.addAttribute(NSAttributedString.Key.kern, value: 2, range: NSMakeRange(0, attrString.length))


// Swift 4.1--
// Line spacing attribute
attrString.addAttribute(NSAttributedStringKey.paragraphStyle, value: style, range: NSRange(location: 0, length: stringValue.characters.count))

// Character spacing attribute
attrString.addAttribute(NSAttributedStringKey.kern, value: 2, range: NSMakeRange(0, attrString.length))

label.attributedText = attrString

Swift 3

let label = UILabel()
let stringValue = "How to\ncontrol\nthe\nline spacing\nin UILabel"
let attrString = NSMutableAttributedString(string: stringValue)
var style = NSMutableParagraphStyle()
style.lineSpacing = 24 // change line spacing between paragraph like 36 or 48
style.minimumLineHeight = 20 // change line spacing between each line like 30 or 40
attrString.addAttribute(NSParagraphStyleAttributeName, value: style, range: NSRange(location: 0, length: stringValue.characters.count))
label.attributedText = attrString