override func viewDidLoad() {
 super.viewDidLoad()
 // 替換 tabbar
 let _tabBar = TabBar()
 // 監(jiān)聽按鈕點擊事件
 _tabBar.handleBtnReleaseClick(self, action: #selector(btnReleaseClick))
 setValue(_tabBar, forKey: "tabBar")
}

// MARK: 刪除占位“按鈕”，添加自定義按鈕
override func layoutSubviews() {
 super.layoutSubviews()
 btnRelease.backgroundColor = UIColor.white
 // 過濾掉 _UIBarBackground 類型的對象，只保留 UITabBarButton 類型的對象
 let tabbarButtonList = iews.filter{NSStringFromClass(type(of: $0)) == abBarButton"}
 // 取出需要刪除的“按鈕”（經(jīng)測試，知道中間那個加號按鈕的下標是2）
 let tmpView = tabbarButtonList[safe: 2]
 // 把默認生成的從父容器中移除
 tmpView?.removeFromSuperview()
 let x = (InnerConst.ScreenW - btnRelease.w) * 0.5
 let y = InnerConst.ButtonOffsetY
 btnRelease.origin = CGPoint(x: x, y: y)
 addSubview(btnRelease)
}

// MARK: 處理默認情況下，按鈕超出 TabBar 以外區(qū)域不能點擊問題
override func hitTest(_ point: CGPoint, with event: UIEvent?) -View? {
 if isHidden == false {
  let newPoint = convert(point, to: btnRelease)
  if btnRelease.point(inside: newPoint, with: event) {
   return btnRelease
  }
  return super.hitTest(point, with: event)
 }
 return super.hitTest(point, with: event)
}

func handleBtnReleaseClick(_ target: AnyObject?, action: Selector) {
 btnRelease.addTarget(target, action: action, for: .touchUpInside)
}