如何更改导航栏(UISearchController)的文本？

let searchController = UISearchController(searchResultsController: nil)
navigationItem.searchController = searchController

searchController.searchBar.placeholder = "搜索"
searchController.searchBar.tintColor = UIColor.white
searchController.searchBar.barTintColor = UIColor.black

if let textField = searchController.searchBar.value(forKey: "searchField") as? UITextField {
    textField.textColor = UIColor.white
}

searchController.searchBar.setValue("取消", forKey: "cancelButtonText")

searchController.searchBar.backgroundImage = UIImage(named: "searchBarBackground")

searchController.searchBar.backgroundColor = UIColor.black

searchController.searchBar.searchBarStyle = .minimal

searchController.searchBar.setImage(UIImage(named: "searchIcon"), for: .search, state: .normal)