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