解决方法
我用这段代码解决了它：
override func viewWillDisappear(animated: Bool) {
self.navigationController?.setNavigationBarHidden(false,animated: animated);
super.viewWillDisappear(animated)
}
override func viewWillAppear(animated: Bool) {
super.viewWillAppear(animated)
self.navigationController?.setNavigationBarHidden(true,animated: animated)
}
