swif 4.1 自定義含有 subtitle 的 titleView

    // MARK:自定義 TitleView
    func setTitle(title:String, subtitle:String) -> UIView {
        
        let titleLabel = UILabel(frame: CGRect(x: 0, y: -2, width: 0, height: 0))
        titleLabel.backgroundColor = UIColor.clear
        titleLabel.textColor = UIColor.gray
        titleLabel.font = UIFont.boldSystemFont(ofSize: 17)
        titleLabel.text = title
        titleLabel.sizeToFit()
        
        let subtitleLabel = UILabel(frame: CGRect(x: 0, y: 18, width: 0, height: 0))
        subtitleLabel.backgroundColor = UIColor.clear
        subtitleLabel.textColor = UIColor.black
        subtitleLabel.font = UIFont.systemFont(ofSize: 12)
        subtitleLabel.text = subtitle
        subtitleLabel.sizeToFit()
        
        let titleView = UIView(frame: CGRect(x: 0, y: 0, width: max(titleLabel.frame.size.width, subtitleLabel.frame.size.width), height: 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
    }

調用方法，在 viewDidLoad() 中調用

self.navigationItem.titleView = setTitle(title: "書架", subtitle: "已選擇1本")

效果圖：

custom titleView