以编程方式在indexpath.item中呈现UIViewController (嵌入到UITabBarController中

// 创建一个UITabBarController实例
let tabBarController = UITabBarController()

// 获取indexPath.item的值，即当前选项卡的索引
let itemIndex = indexPath.item

// 根据itemIndex实例化相应的UIViewController对象
var viewController: UIViewController?

if itemIndex == 0 {
    viewController = storyboard?.instantiateViewController(withIdentifier: "FirstViewController")
} else if itemIndex == 1 {
    viewController = storyboard?.instantiateViewController(withIdentifier: "SecondViewController")
} else if itemIndex == 2 {
    viewController = storyboard?.instantiateViewController(withIdentifier: "ThirdViewController")
}

// 设置选项卡的标题和图标
viewController?.tabBarItem = UITabBarItem(title: "Tab \(itemIndex+1)", image: UIImage(named: "tab\(itemIndex+1)"), tag: itemIndex)

// 将实例化的UIViewController对象添加到UITabBarController的视图控制器数组中
if let viewController = viewController {
    tabBarController.viewControllers = [viewController]
}

// 将UITabBarController设置为应用程序的根视图控制器
UIApplication.shared.keyWindow?.rootViewController = tabBarController