在一个非常罕见的情况下，使用自定义segue，最顶层的视图控制器不在导航堆栈或选项卡栏控制器中或被呈现，但它的视图被插入到关键窗口子视图的顶部。

在这种情况下，有必要检查UIApplication.shared.keyWindow.subviews.last == self。视图来确定当前视图控制器是否是最顶端的。

iOS13+ //top最多视图控制器

extension UIViewController {
    func topMostViewController() -> UIViewController {
        if self.presentedViewController == nil {
            return self
        }
        if let navigation = self.presentedViewController as? UINavigationController {
            return navigation.visibleViewController!.topMostViewController()
        }
        if let tab = self.presentedViewController as? UITabBarController {
            if let selectedTab = tab.selectedViewController {
                return selectedTab.topMostViewController()
            }
            return tab.topMostViewController()
        }
        return self.presentedViewController!.topMostViewController()
    }
}

extension UIApplication {
    func topMostViewController() -> UIViewController? {
        return UIWindow.key!.rootViewController?.topMostViewController()
    }
}

extension UIWindow {
    static var key: UIWindow? {
        if #available(iOS 13, *) {
            return UIApplication.shared.windows.first { $0.isKeyWindow }
        } else {
            return UIApplication.shared.keyWindow
        }
    }
}

//use let vc = UIApplication.shared.topMostViewController()

// End top Most view Controller

你把密码放哪了?

我在我的演示中尝试了你的代码，我发现，如果你把代码放进去

func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool { 

将失败，因为关键窗口已经设置。

但我把你的代码放到了视图控制器中

override func viewDidLoad() {

它就是有用。

我使用下面的代码来获得topViewController-

它向后兼容旧的iOS版本，并照顾UIScene太

extension UIApplication {
    func topViewController() -> UIViewController? {
        var topViewController: UIViewController? = nil
        if #available(iOS 13, *) {
            for scene in connectedScenes {
                if let windowScene = scene as? UIWindowScene {
                    for window in windowScene.windows {
                        if window.isKeyWindow {
                            topViewController = window.rootViewController
                        }
                    }
                }
            }
        } else {
            topViewController = keyWindow?.rootViewController
        }
        while true {
            if let presented = topViewController?.presentedViewController {
                topViewController = presented
            } else if let navController = topViewController as? UINavigationController {
                topViewController = navController.topViewController
            } else if let tabBarController = topViewController as? UITabBarController {
                topViewController = tabBarController.selectedViewController
            } else {
                // Handle any other third party container in `else if` if required
                break
            }
        }
        return topViewController
    }
}

它可以这样使用:

let topController = UIApplication.shared.topViewController()
topController?.present(controllerToPresent, animated: true, completion: nil)

对我来说，最好的解决方案是一个带有函数的扩展。 用这个扩展名创建一个swift文件

首先是UIWindow扩展:

public extension UIWindow {
    var visibleViewController: UIViewController? {
        return UIWindow.visibleVC(vc: self.rootViewController)
    }

    static func visibleVC(vc: UIViewController?) -> UIViewController? {
        if let navigationViewController = vc as? UINavigationController {
            return UIWindow.visibleVC(vc: navigationViewController.visibleViewController)
        } else if let tabBarVC = vc as? UITabBarController {
            return UIWindow.visibleVC(vc: tabBarVC.selectedViewController)
        } else {
            if let presentedVC = vc?.presentedViewController {
                return UIWindow.visibleVC(vc: presentedVC)
            } else {
                return vc
            }
        }
    }
}

在该文件中添加函数

func visibleViewController() -> UIViewController? {
    let appDelegate = UIApplication.shared.delegate
    if let window = appDelegate!.window {
        return window?.visibleViewController
    }
    return nil
}

如果你想使用它，你可以在任何地方调用它。 例子:

  override func viewDidLoad() {
    super.viewDidLoad()
      if let topVC = visibleViewController() {
             //show some label or text field 
    }
}

文件代码如下:

import UIKit

public extension UIWindow {
    var visibleViewController: UIViewController? {
        return UIWindow.visibleVC(vc: self.rootViewController)
    }

    static func visibleVC(vc: UIViewController?) -> UIViewController? {
        if let navigationViewController = vc as? UINavigationController {
            return UIWindow.visibleVC(vc: navigationViewController.visibleViewController)
        } else if let tabBarVC = vc as? UITabBarController {
            return UIWindow.visibleVC(vc: tabBarVC.selectedViewController)
        } else {
            if let presentedVC = vc?.presentedViewController {
                return UIWindow.visibleVC(vc: presentedVC)
            } else {
                return vc
            }
        }
    }
}

func visibleViewController() -> UIViewController? {
    let appDelegate = UIApplication.shared.delegate
    if let window = appDelegate!.window {
        return window?.visibleViewController
    }
    return nil
}

extension UIWindow {

    func visibleViewController() -> UIViewController? {
        if let rootViewController: UIViewController = self.rootViewController {
            return UIWindow.getVisibleViewControllerFrom(vc: rootViewController)
        }
        return nil
    }

    static func getVisibleViewControllerFrom(vc:UIViewController) -> UIViewController {
        if let navigationController = vc as? UINavigationController,
            let visibleController = navigationController.visibleViewController  {
            return UIWindow.getVisibleViewControllerFrom( vc: visibleController )
        } else if let tabBarController = vc as? UITabBarController,
            let selectedTabController = tabBarController.selectedViewController {
            return UIWindow.getVisibleViewControllerFrom(vc: selectedTabController )
        } else {
            if let presentedViewController = vc.presentedViewController {
                return UIWindow.getVisibleViewControllerFrom(vc: presentedViewController)
            } else {
                return vc
            }
        }
    }
}

用法:

if let topController = window.visibleViewController() {
    println(topController)
}