fileprivate let lxfFlag: Int = 666
extension UITabBar {
 // MARK:- 显示小红点
 func showBadgOn(index itemIndex: Int, tabbarItemNums: CGFloat = 4.0) {
  // 移除之前的小红点
  self.removeBadgeOn(index: itemIndex)
  // 创建小红点
  let bageView = UIView()
  bageView.tag = itemIndex + lxfFlag
  bageView.layer.cornerRadius = 5
  bageView.backgroundColor = UIColor.red
  let tabFrame = self.frame
  // 确定小红点的位置
  let percentX: CGFloat = (CGFloat(itemIndex) + 0.59) / tabbarItemNums
  let x: CGFloat = CGFloat(ceilf(Float(percentX * tabFrame.size.width)))
  let y: CGFloat = CGFloat(ceilf(Float(0.115 * tabFrame.size.height)))
  bageView.frame = CGRect(x: x, y: y, width: 10, height: 10)
  self.addSubview(bageView)
 }
 // MARK:- 隐藏小红点
 func hideBadg(on itemIndex: Int) {
  // 移除小红点
  self.removeBadgeOn(index: itemIndex)
 }
 // MARK:- 移除小红点
 fileprivate func removeBadgeOn(index itemIndex: Int) {
  // 按照tag值进行移除
  _ = subviews.map {
   if $0.tag == itemIndex + lxfFlag {
    $0.removeFromSuperview()
   }
  }
 }
}

// 默认4个tabbarItem
self.tabBarController?.tabBar.showBadgOn(index: 2)
// 如果不是则用这个方法
// self.tabBarController?.tabBar.showBadgOn(index: Int, tabbarItemNums: CGFloat)