two lines title for navigationbar

two lines title for navigationbar.swift

//http://stackoverflow.com/questions/2422383/uinavigationbar-multi-line-title
private func setupTitleView() {
    let topText = NSLocalizedString("key", comment: "")
    let bottomText = NSLocalizedString("key", comment: "")

    let titleParameters = [NSForegroundColorAttributeName : UIColor.<Color>(),
                           NSFontAttributeName : UIFont.<Font>]
    let subtitleParameters = [NSForegroundColorAttributeName : UIColor.<Color>(),
                              NSFontAttributeName : UIFont.<Font>]

    let title:NSMutableAttributedString = NSMutableAttributedString(string: topText, attributes: titleParameters)
    let subtitle:NSAttributedString = NSAttributedString(string: bottomText, attributes: subtitleParameters)

    title.appendAttributedString(NSAttributedString(string: "\n"))
    title.appendAttributedString(subtitle)

    let size = title.size()

    let width = size.width
    guard let height = navigationController?.navigationBar.frame.size.height else {return}

    let titleLabel = UILabel(frame: CGRectMake(0,0, width, height))
    titleLabel.attributedText = title
    titleLabel.numberOfLines = 0
    titleLabel.textAlignment = .Center

    navigationItem.titleView = titleLabel
}

thank you for the code. I am still new to Xcode and swift. I do most of the work in the storyboard. My question is, where do I paste the code above.