下面是一个简单的红色斑点githubGist的例子。当然，如果你想在里面添加一个标签，你可以自定义你自己的badgeView = UIView()。

Swift 4.2

fileprivate let tabBarItemTag: Int = 10090
extension UITabBar {
    public func addItemBadge(atIndex index: Int) {
        guard let itemCount = self.items?.count, itemCount > 0 else {
            return
        }
        guard index < itemCount else {
            return
        }
        removeItemBadge(atIndex: index)

        let badgeView = UIView()
        badgeView.tag = tabBarItemTag + Int(index)
        badgeView.layer.cornerRadius = 5
        badgeView.backgroundColor = UIColor.red

        let tabFrame = self.frame
        let percentX = (CGFloat(index) + 0.56) / CGFloat(itemCount)
        let x = (percentX * tabFrame.size.width).rounded(.up)
        let y = (CGFloat(0.1) * tabFrame.size.height).rounded(.up)
        badgeView.frame = CGRect(x: x, y: y, width: 10, height: 10)
        addSubview(badgeView)
    }

    //return true if removed success.
    @discardableResult
    public func removeItemBadge(atIndex index: Int) -> Bool {
        for subView in self.subviews {
            if subView.tag == (tabBarItemTag + index) {
                subView.removeFromSuperview()
                return true
            }
        }
        return false
    }
}

试试这个：

func repositionBadge(tabIndex: Int){

    for badgeView in self.tabBarController!.tabBar.subviews[tabIndex].subviews {

        if NSStringFromClass(badgeView.classForCoder) == "_UIBadgeView" {
            badgeView.layer.transform = CATransform3DIdentity
            badgeView.layer.transform = CATransform3DMakeTranslation(-17.0, 1.0, 1.0)
        }
    }
}

注意，tabIndex从1开始

基于Marco Santarossa的answer，我将其更新为UITabBarController扩展，并进行了一些额外的调整：

extension UITabBarController {
    func repositionBadgeLayer(_ badgeView: UIView) {
        if NSStringFromClass(badgeView.classForCoder) == "_UIBadgeView" {
            badgeView.layer.transform = CATransform3DIdentity
            badgeView.layer.transform = CATransform3DMakeTranslation(-17.0, 1.0, 1.0)
        }
    }

    func repositionBadges(tab: Int? = nil) {
        if let tabIndex = tab {
            for badgeView in self.tabBar.subviews[tabIndex].subviews {
                repositionBadgeLayer(badgeView)
            }
        } else {
            for tabBarSubviews in self.tabBar.subviews {
                for badgeView in tabBarSubviews.subviews {
                    repositionBadgeLayer(badgeView)
                }
            }
        }
    }
}

现在你可以在你的自定义UITabBarController类上使用它，只需调用：

1. repositionBadges()应用于选项卡栏中可用的每个选项卡栏项目

或

1. repositionBadges(0)，其中0指选项卡栏项索引，用于选择性应用

我不确定转换徽章层是否可以孤立，因为它有一些缺陷：

• 选项卡选择后将重置
• 徽章标签一变它就不停的变

我想到了另一个解决办法

if UIDevice.current.userInterfaceIdiom == .pad {
        self.standatartTabBarAppearance.inlineLayoutAppearance.normal.badgePositionAdjustment.horizontal = .init(16.0)
        self.standatartTabBarAppearance.stackedLayoutAppearance.normal.badgePositionAdjustment.horizontal = .init(16.0)
        self.standatartTabBarAppearance.compactInlineLayoutAppearance.normal.badgePositionAdjustment.horizontal = .init(16.0)
    }
self.tabBar.standardAppearance = self.standatartTabBarAppearance

iOS 13或更高版本时，可以通过将UITabBarItemAppearance对象分配给UITabBarAppearance对象的项目外观属性，并将其分配给tabBar控件的appearance属性来更改徽章位置。
示例：

let itemAppearance = UITabBarItemAppearance()
 itemAppearance.normal.badgePositionAdjustment.horizontal = 10
    
 let appearance = UITabBarAppearance()
 appearance.stackedLayoutAppearance = itemAppearance
 appearance.inlineLayoutAppearance = itemAppearance
 appearance.compactInlineLayoutAppearance = itemAppearance

 tabBar.standardAppearance = appearance