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 self.keyWindow?.rootViewController?.topMostViewController()
    }
}

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。

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
}

在SWIFT 5.2中

你可以使用下面的代码:

import UIKit

extension UIWindow {
    static func getTopViewController() -> UIViewController? {
        if #available(iOS 13, *){
            let keyWindow = UIApplication.shared.windows.filter {$0.isKeyWindow}.first
            
            if var topController = keyWindow?.rootViewController {
                while let presentedViewController = topController.presentedViewController {
                    topController = presentedViewController
                }
                return topController
            }
        } else {
            if var topController = UIApplication.shared.keyWindow?.rootViewController {
                while let presentedViewController = topController.presentedViewController {
                    topController = presentedViewController
                }
                return topController
            }
        }
        return nil
    }
}

斯威夫特 5+

声明

func topViewController() -> UIViewController? {
    
    let keyWindow = UIApplication.shared.windows.filter {$0.isKeyWindow}.first

    if var topController = keyWindow?.rootViewController {
        
        while let presentedViewController = topController.presentedViewController {
            topController = presentedViewController
        }
        
        return topController
        
    } else {
        
        return nil
        
    }
    
}

Use

topViewController()?.view.addSubview(UIView())

  var topViewController: UIViewController? {
        guard var topViewController = UIApplication.shared.keyWindow?.rootViewController else { return nil }
        while let presentedViewController = topViewController.presentedViewController {
            topViewController = presentedViewController
        }
        return topViewController
    }