Add subtitle under the title in navigation bar controller in Xcode

Here is my version using a stack view on an extension.

extension UINavigationItem {
    func setTitle(title:String, subtitle:String) {
        
        let one = UILabel()
        one.text = title
        one.font = UIFont.systemFont(ofSize: 17)
        one.sizeToFit()
        
        let two = UILabel()
        two.text = subtitle
        two.font = UIFont.systemFont(ofSize: 12)
        two.textAlignment = .center
        two.sizeToFit()
        
        let stackView = UIStackView(arrangedSubviews: [one, two])
        stackView.distribution = .equalCentering
        stackView.axis = .vertical
        stackView.alignment = .center
        
        let width = max(one.frame.size.width, two.frame.size.width)
        stackView.frame = CGRect(x: 0, y: 0, width: width, height: 35)
        
        one.sizeToFit()
        two.sizeToFit()
        
        self.titleView = stackView
    }
}

Though there is a solution but it has some known issues

Solution is writing a function like this

func setTitle(title:String, subtitle:String) -> UIView {
    let titleLabel = UILabel(frame: CGRectMake(0, -2, 0, 0))

    titleLabel.backgroundColor = UIColor.clearColor()
    titleLabel.textColor = UIColor.grayColor()
    titleLabel.font = UIFont.boldSystemFontOfSize(17)
    titleLabel.text = title
    titleLabel.sizeToFit()

    let subtitleLabel = UILabel(frame: CGRectMake(0, 18, 0, 0))
    subtitleLabel.backgroundColor = UIColor.clearColor()
    subtitleLabel.textColor = UIColor.blackColor()
    subtitleLabel.font = UIFont.systemFontOfSize(12)
    subtitleLabel.text = subtitle
    subtitleLabel.sizeToFit()

    let titleView = UIView(frame: CGRectMake(0, 0, max(titleLabel.frame.size.width, subtitleLabel.frame.size.width), 30))
    titleView.addSubview(titleLabel)
    titleView.addSubview(subtitleLabel)

    let widthDiff = subtitleLabel.frame.size.width - titleLabel.frame.size.width

    if widthDiff < 0 {
        let newX = widthDiff / 2
        subtitleLabel.frame.origin.x = abs(newX)
    } else {
        let newX = widthDiff / 2
        titleLabel.frame.origin.x = newX
    }

    return titleView
}

Using this function for custom navigation title view in viewDidLoad

self.navigationItem.titleView = setTitle("Title", subtitle: "SubTitle")

Only known issue is that if subtitle becomes very large than the misplacement occurs.

Final Outcome

Source: https://gist.github.com/nazywamsiepawel/0166e8a71d74e96c7898

@iosjillian's Swift 4 extension works great, adding a bit more to honor the bar's appearance and user font preferences:

import UIKit

extension UINavigationItem {

  func setTitle(_ title: String, subtitle: String) {
    let appearance = UINavigationBar.appearance()
    let textColor = appearance.titleTextAttributes?[NSAttributedString.Key.foregroundColor] as? UIColor ?? .black

    let titleLabel = UILabel()
    titleLabel.text = title
    titleLabel.font = .preferredFont(forTextStyle: UIFont.TextStyle.headline)
    titleLabel.textColor = textColor

    let subtitleLabel = UILabel()
    subtitleLabel.text = subtitle
    subtitleLabel.font = .preferredFont(forTextStyle: UIFont.TextStyle.subheadline)
    subtitleLabel.textColor = textColor.withAlphaComponent(0.75)

    let stackView = UIStackView(arrangedSubviews: [titleLabel, subtitleLabel])
    stackView.distribution = .equalCentering
    stackView.alignment = .center
    stackView.axis = .vertical

    self.titleView = stackView
  }
}

Thanks a lot for your answer! @RajanMaheshwari

Your coding worked perfectly except the if statement you made with the widthDiff..

I adjusted it a little bit and everything worked smoothly.

if widthDiff < 0 {
        let newX = widthDiff / 2
        subtitleLabel.frame.origin.x = abs(newX)
    } else {
        let newX = widthDiff / 2
        titleLabel.frame.origin.x = newX
    }

Thanks again for your response!

I really liked @user2325031's answer, but found that sizing the labels to fit and setting the frame wasn't needed. I also set the stackView's alignment to .center per @GerardoMR's suggestion.

extension UINavigationItem {

    func setTitle(_ title: String, subtitle: String) {
        let titleLabel = UILabel()
        titleLabel.text = title
        titleLabel.font = .systemFont(ofSize: 17.0)
        titleLabel.textColor = .black

        let subtitleLabel = UILabel()
        subtitleLabel.text = subtitle
        subtitleLabel.font = .systemFont(ofSize: 12.0)
        subtitleLabel.textColor = .gray

        let stackView = UIStackView(arrangedSubviews: [titleLabel, subtitleLabel])
        stackView.distribution = .equalCentering
        stackView.alignment = .center
        stackView.axis = .vertical

        self.titleView = stackView
    }

}