系统tabbar选中和未选中文字颜色修改记录

需要，tabbar顶部无横线，不带模糊和透明度效果，遇到小坑，特此记录,
appearance 和 unselectedItemTintColor 不可兼得，只能取其一。

        tabBarController.tabBar.tintColor = UIColor.white
        tabBarController.tabBar.unselectedItemTintColor = UIColor.white.withAlphaComponent(0.5)
        tabBarController.tabBar.barTintColor = #colorLiteral(red: 0.6392156863, green: 0.6862745098, blue: 0.8, alpha: 1)
        tabBarController.tabBar.shadowImage = UIImage()
        tabBarController.tabBar.backgroundImage = UIImage(named: "tabbarBg")
//       if #available(iOS 13, *) {
//           let appearance = tabBarController.tabBar.standardAppearance.copy();
//           appearance.backgroundColor = #colorLiteral(red: 0.6392156863, green: 0.6862745098, blue: 0.8, alpha: 1)
//           appearance.shadowImage = UIImage(named: "alpha");
//          appearance.configureWithTransparentBackground();
//           tabBarController.tabBar.standardAppearance = appearance;
//       } else {
//           tabBarController.tabBar.backgroundImage = UIImage();
//           tabBarController.tabBar.shadowImage = UIImage();
//       }