Swift 3 - Adjust Font Size to Fit Width, Multiple Lines

Question

I have a UILabel and it is set to 42.0 pt font, and the width of the label is set using autoconstraints based on factors other than the label itself (aka the things to the right

Answer 1

Swift 5

func setFontForLabel(label:UILabel, maxFontSize:CGFloat, minFontSize:CGFloat, maxLines:Int) {

    var numLines: Int = 1
    var textSize: CGSize = CGSize.zero
    var frameSize: CGSize = CGSize.zero
    let font: UIFont = label.font.withSize(maxFontSize)

    frameSize = label.frame.size

    textSize = (label.text! as NSString).size(withAttributes: [NSAttributedString.Key.font: font])

    // Determine number of lines
    while ((textSize.width/CGFloat(numLines)) / (textSize.height * CGFloat(numLines)) > frameSize.width / frameSize.height) && numLines < maxLines {
        numLines += 1
    }

    label.font = font
    label.adjustsFontSizeToFitWidth = true
    label.numberOfLines = numLines
    label.minimumScaleFactor = minFontSize/maxFontSize
}

Swift 3

I looked at the post that paper111 posted. Unfortunately it's in Obj-C and the sizeWithFont: ,constrainedToSize: , lineBreakMode: method has been deprecated. (- - );

His answer was good, but still didn't provide a fixed size. What I did was to start with a UILabel that had everything but the height (this is probably the same for most people).

let myFrame = CGRect(x: 0, y:0, width: 200, height: self.view.height)
let myLbl = UILabel(frame: myFrame)
let finalHeight:CGFloat = 300

myLbl.font = UIFont(name: "Chalkduster", size: 16.0)
myLbl.lineBreakMode = .byWordWrapping
myLbl.numberOfLines = 0
myLbl.text = "Imagine your long line of text here"
addSubview(myLbl)
myLbl.sizeToFit()

guard myLbl.frame.height > finalHeight else { return }
var fSize:CGFloat = 16 //start with the default font size
    repeat {
        fSize -= 2
        myLbl.font = UIFont(name: "Chalkduster", size: fSize)
        myLbl.sizeToFit()
    } while myLbl.frame.height > finalHeight

You can see that there's a guard blocking the resize if it's not needed. Also, calling sizeToFit() many times isn't ideal, but I can't think of another way around it. I tried to use myLbl.font.withSize(fSize) in the loop but it wouldn't work, so I used the full method instead.

Hope it works for you!