跳转到当前页面时隐藏导航栏，返回上一级时显示导航栏
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
self.navigationController?.navigationBar.isHidden = true
}
override func viewWillDisappear(_ animated: Bool) {
super.viewWillDisappear(animated)
self.navigationController?.navigationBar.isHidden = false
}
场景：
当前控制器有标签栏，点击跳转到下一个界面时，需要隐藏标签栏，返回当前控制器时，标签栏又显示
vc.hidesBottomBarWhenPushed = true
