iOS 13 之前， 去掉黑线：设置UITarBar的 backgroundImage 和 shadowImage即可：

        tabbar.backgroundImage = UIImage(color: UIColor.clear)

        tabbar.shadowImage = UIImage(color: UIColor.clear)

iOS13之后不好使了，改用下面的方法：

        let appearance = tabbar.standardAppearance.copy()

        appearance.backgroundImage = UIImage(color: UIColor.clear)

        appearance.shadowImage = UIImage(color: UIColor.clear)

        tabbar.standardAppearance = appearance

1

所以兼容代码如下：

    if #available(iOS 13, *) {

        let appearance = tabbar.standardAppearance.copy()

        appearance.backgroundImage = UIImage(color: UIColor.clear)

        appearance.shadowImage = UIImage(color: UIColor.clear)

        tabbar.standardAppearance = appearance

    } else {

        tabbar.backgroundImage = UIImage(color: UIColor.clear)

        tabbar.shadowImage = UIImage(color: UIColor.clear)

    }