呈现View时导航栏不显示？

Question

选择此行代码时，导航栏不会出现

  self.present(vc, animated: true, completion: nil)

但是在试用这段代码时

let vc = storyboard.instantiateViewController(withIdentifier: "view")
let navController = UINavigationController(rootViewController: vc)
self.present(vc, animated: true, completion: nil)

我的应用崩溃，发出错误

NSInvalidArgumentException', reason: 'Application tried to present modally an active controller 

在呈现视图而不是推动视图时，请帮助我获取导航栏

Answer 1

尝试这样做 -

self.present(navController, animated: true, completion: nil)