override func viewDidAppear(animated: Bool) {
        super.viewDidAppear(animated)

        btnTwoLine?.titleLabel?.lineBreakMode = NSLineBreakMode.ByWordWrapping;
}

@IBOutlet weak var btnTwoLine: UIButton?

override func viewDidAppear(animated: Bool) {
        super.viewDidAppear(animated)

        //applying the line break mode
        btnTwoLine?.titleLabel?.lineBreakMode = NSLineBreakMode.ByWordWrapping;

        var buttonText: NSString = "hellonthere"

        //getting the range to separate the button title strings
        var newlineRange: NSRange = buttonText.rangeOfString("n")

        //getting both substrings
        var substring1: NSString = ""
        var substring2: NSString = ""

        if(newlineRange.location != NSNotFound) {
            substring1 = buttonText.substringToIndex(newlineRange.location)
            substring2 = buttonText.substringFromIndex(newlineRange.location)
        }

        //assigning diffrent fonts to both substrings
        let font:UIFont? = UIFont(name: "Arial", size: 17.0)
        let attrString = NSMutableAttributedString(
            string: substring1 as String,
            attributes: NSDictionary(
                object: font!,
                forKey: NSFontAttributeName) as [NSObject : AnyObject])

        let font1:UIFont? = UIFont(name: "Arial", size: 11.0)
        let attrString1 = NSMutableAttributedString(
            string: substring2 as String,
            attributes: NSDictionary(
                object: font1!,
                forKey: NSFontAttributeName) as [NSObject : AnyObject])

        //appending both attributed strings
        attrString.appendAttributedString(attrString1)

        //assigning the resultant attributed strings to the button
        btnTwoLine?.setAttributedTitle(attrString, forState: UIControlState.Normal)

    }

let str = NSMutableAttributedString(string: "First linenSecond Line")
str.addAttribute(NSFontAttributeName, value: UIFont.systemFont(ofSize: 17), range: NSMakeRange(0, 10))
str.addAttribute(NSFontAttributeName, value: UIFont.systemFont(ofSize: 12), range: NSMakeRange(11, 11))
button.setAttributedTitle(str, for: .normal)

override func viewDidLoad() {
        super.viewDidLoad()
        var str = NSMutableAttributedString(string: "First linenSecond Line")
        str.addAttribute(NSFontAttributeName, value: UIFont.systemFontOfSize(17), range: NSMakeRange(0, 10))
        str.addAttribute(NSFontAttributeName, value: UIFont.systemFontOfSize(12), range: NSMakeRange(11, 11))
        button.setAttributedTitle(str, forState: .Normal)

    }

let firstLabel = UILabel()

    firstLabel.backgroundColor = UIColor.lightGrayColor()
    firstLabel.text = "Hi"
    firstLabel.textColor = UIColor.blueColor()
    firstLabel.textAlignment = NSTextAlignment.Center
    firstLabel.frame = CGRectMake(0, testButton.frame.height * 0.25, testButton.frame.width, testButton.frame.height * 0.2)
    testButton.addSubview(firstLabel)

    let secondLabel = UILabel()

    secondLabel.backgroundColor = UIColor.lightGrayColor()
    secondLabel.textColor = UIColor.blueColor()
    secondLabel.font = UIFont(name: "Arial", size: 12)
    secondLabel.text = "There"
    secondLabel.textAlignment = NSTextAlignment.Center
    secondLabel.frame = CGRectMake(0, testButton.frame.height * 0.5, testButton.frame.width, testButton.frame.height * 0.2)
    testButton.addSubview(secondLabel)

let button = UIButton()
    button.titleLabel?.numberOfLines = 0
    button.titleLabel?.lineBreakMode = .byWordWrapping
    button.setTitle("FoonBar", for: .normal)
    button.titleLabel?.textAlignment = .center
    button.sizeToFit()
    button.addTarget(self, action: #selector(rightBarButtonTapped), for: .allEvents)
    navigationItem.rightBarButtonItem = UIBarButtonItem(customView: button)