创建两行大标题导航栏的问题| Swift 5

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        
        // 创建导航栏
        let navigationBar = UINavigationBar(frame: CGRect(x: 0, y: 0, width: view.frame.width, height: 100))
        
        // 创建导航项
        let navigationItem = UINavigationItem()
        
        // 创建第一行标题
        let firstTitleLabel = UILabel()
        firstTitleLabel.text = "第一行标题"
        firstTitleLabel.font = UIFont.boldSystemFont(ofSize: 20)
        
        // 创建第二行标题
        let secondTitleLabel = UILabel()
        secondTitleLabel.text = "第二行标题"
        secondTitleLabel.font = UIFont.systemFont(ofSize: 14)
        
        // 创建标题视图
        let titleView = UIStackView(arrangedSubviews: [firstTitleLabel, secondTitleLabel])
        titleView.axis = .vertical
        titleView.alignment = .center
        
        // 将标题视图设置为导航项的标题视图
        navigationItem.titleView = titleView
        
        // 将导航项添加到导航栏
        navigationBar.items = [navigationItem]
        
        // 将导航栏添加到视图
        view.addSubview(navigationBar)
    }
}