[iOS 13] UITabBarItem 标题颜色设置无效问题

使用新版XcodeVersion 11.2.1 (11B500)创建项目时，发现对UITabController的UITabBarItem中的字体颜色设置无法生效
原来的写法：

UITabBarItem.appearance().setTitleTextAttributes([NSAttributedString.Key.foregroundColor:UIColor.red], for: UIControl.State.normal)
UITabBarItem.appearance().setTitleTextAttributes([NSAttributedString.Key.foregroundColor:UIColor.blue], for: UIControl.State.selected)

或者

if #available(iOS 13.0, *) {
    let array = self.tabBar.items
    for item:UITabBarItem in array! {
        item.setTitleTextAttributes([NSAttributedString.Key.foregroundColor:UIColor.red], for: UIControl.State.selected)
        item.setTitleTextAttributes([NSAttributedString.Key.foregroundColor:UIColor.orange], for: UIControl.State.normal)
    }
}

OC版

[[UITabBarItem appearance] setTitleTextAttributes:@{NSForegroundColorAttributeName:RGB_COLOR(82, 82, 82, 1)} forState:UIControlStateNormal];
[[UITabBarItem appearance] setTitleTextAttributes:@{NSForegroundColorAttributeName:Main_Dominant_Pass_Color} forState:UIControlStateSelected];

经过Google和查看官方文档，在iOS 13中，Apple将设置UITabBarItem的文字属性的任务，交给了13中新添加的属性UITabBarItem.standardAppearance

下面是适配iOS 13的写法：

class TabBarViewController: UITabBarController {
    
    override func viewDidLoad() {
        super.viewDidLoad()

        // Do any additional setup after loading the view.
        
        UITabBarItem.appearance().setTitleTextAttributes([NSAttributedString.Key.foregroundColor:UIColor.red], for: UIControl.State.normal)
        UITabBarItem.appearance().setTitleTextAttributes([NSAttributedString.Key.foregroundColor:UIColor.blue], for: UIControl.State.selected)
        
        
        if #available(iOS 13.0, *) {
            let array = self.tabBar.items
            for item:UITabBarItem in array! {
                item.setTitleTextAttributes([NSAttributedString.Key.foregroundColor:UIColor.red], for: UIControl.State.selected)
                item.setTitleTextAttributes([NSAttributedString.Key.foregroundColor:UIColor.orange], for: UIControl.State.normal)
                
                let uitabApp:UITabBarAppearance = UITabBarAppearance()
                uitabApp.stackedLayoutAppearance.normal.titleTextAttributes = [NSAttributedString.Key.foregroundColor:UIColor.cyan]
                uitabApp.stackedLayoutAppearance.selected.titleTextAttributes = [NSAttributedString.Key.foregroundColor:UIColor.orange]
                item.standardAppearance = uitabApp
            }
        }
    }
}

以上代码均在UITabBarController子类TabBarViewController的viewDidLoad中设定