滑动返回过程取消，导航栏出现三个小点

[fengneng]

在iOS10 以下机型，侧滑返回过程中慢慢取消，导航栏左侧出现三个点，并且很难通过重试消除：

self.navigationController.navigationBar.topItem.title = @"";
self.navigationController.navigationBar.backItem.title = @"";

另一种方案，找到UINavigationItemButtonView 将其隐藏，

`
override func viewDidAppear(animated: Bool) {
super.viewDidAppear(animated)
guard let subviews = navigationController?.navigationBar.subviews else {return}

for view in subviews {
if view.isKindOfClass(NSClassFromString("UINavigationItemButtonView")!) {
view.hidden = true
}}}
`