Rewritten for Swift + UIButton extension

NSString+KBAdditions.swift

//
//  NSString+KBAdditions.swift
//
//  Created by Alexander Mayatsky on 16/03/16.
//
//  Original code from http://stackoverflow.com/a/4383281/463892 & http://stackoverflow.com/a/18951386
//

import Foundation
import UIKit

protocol NSStringKBAdditions {
    func fontSizeWithFont(font: UIFont, constrainedToSize size: CGSize, minimumScaleFactor: CGFloat) -> CGFloat
}

extension NSString : NSStringKBAdditions {
    func fontSizeWithFont(font: UIFont, constrainedToSize size: CGSize, minimumScaleFactor: CGFloat) -> CGFloat {
        var fontSize = font.pointSize
        let minimumFontSize = fontSize * minimumScaleFactor
        
        
        var attributedText = NSAttributedString(string: self as String, attributes:[NSFontAttributeName: font])
        var height = attributedText.boundingRectWithSize(CGSize(width: size.width, height: CGFloat.max), options:NSStringDrawingOptions.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--;
            newFont = UIFont(name: font.fontName, size: fontSize)!
            
            attributedText = NSAttributedString(string: self as String, attributes:[NSFontAttributeName: newFont])
            height = attributedText.boundingRectWithSize(CGSize(width: size.width, height: CGFloat.max), options:NSStringDrawingOptions.UsesLineFragmentOrigin, context:nil).size.height
        }
        
        // Loop through words in string and resize to fit
        for word in self.componentsSeparatedByCharactersInSet(NSCharacterSet.whitespaceAndNewlineCharacterSet()) {
            var width = word.sizeWithAttributes([NSFontAttributeName:newFont]).width
            while (width > size.width && width != 0 && fontSize > minimumFontSize) {
                fontSize--
                newFont = UIFont(name: font.fontName, size: fontSize)!
                width = word.sizeWithAttributes([NSFontAttributeName:newFont]).width
            }
        }
        return fontSize;
    }
}

UIButton+KBAdditions.swift

//
//  UIButton+KBAdditions.swift
//
//  Created by Alexander Mayatsky on 16/03/16.
//
//  Original code from http://stackoverflow.com/a/4383281/463892 & http://stackoverflow.com/a/18951386
//

import Foundation
import UIKit

protocol UIButtonKBAdditions {
    func sizeToFitMultipleLines(sizeToFit: Bool)
}

extension UIButton : UIButtonKBAdditions {
    func sizeToFitMultipleLines(sizeToFit: Bool = false) {
        if let label = self.titleLabel {
            if label.adjustsFontSizeToFitWidth {
                if let text = label.text {
                    let adjustedFontSize = text.fontSizeWithFont(label.font, constrainedToSize:self.frame.size, minimumScaleFactor:label.minimumScaleFactor)
                    label.font = label.font.fontWithSize(adjustedFontSize)
                    if sizeToFit {
                        self.sizeToFit()
                    }
                }
            }
        }
    }
}

UILabel+KBAdditions.swift

//
//  UILabel+KBAdditions.swift
//
//  Created by Alexander Mayatsky on 16/03/16.
//
//  Original code from http://stackoverflow.com/a/4383281/463892 & http://stackoverflow.com/a/18951386
//

import Foundation
import UIKit

protocol UILabelKBAdditions {
    func sizeToFitMultipleLines()
}

extension UILabel : UILabelKBAdditions {
    func sizeToFitMultipleLines() {
        if self.adjustsFontSizeToFitWidth {
            if let text = self.text {
                let adjustedFontSize = text.fontSizeWithFont(self.font, constrainedToSize:self.frame.size, minimumScaleFactor:self.minimumScaleFactor)
                self.font = self.font.fontWithSize(adjustedFontSize)
                self.sizeToFit()
            }
        }
    }
}