，

swift设置根视频，需要用UINavigationController,否则在后面使用导航栏跳转时会 出现导航栏为nil

let view = ViewController()
        let nav = UINavigationController(rootViewController: view)
        window = UIWindow(windowScene: scene as! UIWindowScene)
        window?.rootViewController = nav

但是登录页面一般不需要导航栏，所以我们需要在登录视图中对导航栏的显示进行控制

 /*将显示界面隐藏导航栏*/
    override func viewWillAppear(_ animated: Bool) {
        self.navigationController?.navigationBar.isHidden = true
       
    }
    /*将消失界面显示导航栏*/
    override func viewWillDisappear(_ animated: Bool) {
        self.navigationController?.navigationBar.isHidden = false
        
    }

下面是登出操作

let view = ViewController() // 
        let nav = UINavigationController(rootViewController: view)
        self.view.window?.rootViewController = nav