Multiline UILabel with adjustsFontSizeToFitWidth

Question

I have a multiline UILabel whose font size I\'d like to adjust depending on the text length. The whole text should fit into the label\'s frame without truncating it.

Answer 1

Swift 4.2:

//
//  String+Utility.swift
//
//  Created by Philip Engberg on 29/11/2018.
//  Original code from http://stackoverflow.com/a/4383281/463892 & http://stackoverflow.com/a/18951386
//

import Foundation
import UIKit

extension String {
    func fontSize(with font: UIFont, constrainedTo size: CGSize, minimumScaleFactor: CGFloat) -> CGFloat {
        var fontSize = font.pointSize
        let minimumFontSize = fontSize * minimumScaleFactor

        var attributedText = NSAttributedString(string: self, attributes: [.font: font])
        var height = attributedText.boundingRect(with: CGSize(width: size.width, height: CGFloat.greatestFiniteMagnitude), options: [.usesLineFragmentOrigin], context: nil).size.height

        var newFont = font
        //Reduce font size while too large, break if no height (empty string)
        while height > size.height && height != 0 && fontSize > minimumFontSize {
            fontSize -= 1
            newFont = UIFont(name: font.fontName, size: fontSize)!

            attributedText = NSAttributedString(string: self, attributes: [.font: newFont])
            height = attributedText.boundingRect(with: CGSize(width: size.width, height: CGFloat.greatestFiniteMagnitude), options: [.usesLineFragmentOrigin], context: nil).size.height
        }

        // Loop through words in string and resize to fit
        for word in self.components(separatedBy: NSCharacterSet.whitespacesAndNewlines) {
            var width = word.size(withAttributes: [.font: newFont]).width
            while width > size.width && width != 0 && fontSize > minimumFontSize {
                fontSize -= 1
                newFont = UIFont(name: font.fontName, size: fontSize)!
                width = word.size(withAttributes: [.font: newFont]).width
            }
        }
        return fontSize
    }
}

Answer 2

Thought I would add my own take on the answer:

I think it's a slight improvement on some of the other answers because:

1. Caching while looping through words to find the longest by width, to prevent unnecessary calculations
2. All the label attributes are used when doing size calculations

https://gist.github.com/chrisjrex/c571056a4b621f7099bcbd5e179f184f

Note: This solution should only be used when a UILabel has .numberOfLines = 0 and .lineBreakMode = .byWordWrapping

Otherwise you are better off using: .adjustFontSizeForWidth = true from the standard swift library

The other answers on this thread were very helpful to me in coming up with my solution, thank you