最新Swift版本: 创建一个文件，命名为UIWindowExtension.swift，并粘贴以下代码片段:

import UIKit

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

    public static func getVisibleViewControllerFrom(_ vc: UIViewController?) -> UIViewController? {
        if let nc = vc as? UINavigationController {
            return UIWindow.getVisibleViewControllerFrom(nc.visibleViewController)
        } else if let tc = vc as? UITabBarController {
            return UIWindow.getVisibleViewControllerFrom(tc.selectedViewController)
        } else {
            if let pvc = vc?.presentedViewController {
                return UIWindow.getVisibleViewControllerFrom(pvc)
            } else {
                return vc
            }
        }
    }
}

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

可以在任何地方使用:

if let topVC = getTopViewController() {

}

iOS 4在UIWindow上引入了rootViewController属性:

[UIApplication sharedApplication].keyWindow.rootViewController;

你需要在创建视图控制器后自己设置。

@implementation UIWindow (Extensions)

- (UIViewController*) topMostController
{
    UIViewController *topController = [self rootViewController];

    while (topController.presentedViewController) {
        topController = topController.presentedViewController;
    }

    return topController;
}

@end

我知道已经很晚了，可能是多余的。但以下是我提出的对我有用的片段:

    static func topViewController() -> UIViewController? {
        return topViewController(vc: UIApplication.shared.keyWindow?.rootViewController)
    }

    private static func topViewController(vc:UIViewController?) -> UIViewController? {
        if let rootVC = vc {
            guard let presentedVC = rootVC.presentedViewController else {
                return rootVC
            }
            if let presentedNavVC = presentedVC as? UINavigationController {
                let lastVC = presentedNavVC.viewControllers.last
                return topViewController(vc: lastVC)
            }
            return topViewController(vc: presentedVC)
        }
        return nil
    }

Swift替代解决方案:

static func topMostController() -> UIViewController {
    var topController = UIApplication.sharedApplication().keyWindow?.rootViewController
    while (topController?.presentedViewController != nil) {
        topController = topController?.presentedViewController
    }

    return topController!
}

下面两个函数可以帮助在视图控制器堆栈中找到topViewController。以后可能需要自定义，但是对于这段代码来说，理解topViewController或viewcontroller堆栈的概念非常棒。

- (UIViewController*)findTopViewController {

  id  topControler  = [self topMostController];

  UIViewController* topViewController;
  if([topControler isKindOfClass:[UINavigationController class]]) {
        topViewController = [[(UINavigationController*)topControler viewControllers] lastObject];
   } else if ([topControler isKindOfClass:[UITabBarController class]]) {
        //Here you can get reference of top viewcontroller from stack of viewcontrollers on UITabBarController
  } else {
        //topController is a preented viewController
        topViewController = (UIViewController*)topControler;
  }
    //NSLog(@"Top ViewController is: %@",NSStringFromClass([topController class]));
    return topViewController;
}

- (UIViewController*)topMostController
{
    UIViewController *topController = [UIApplication sharedApplication].keyWindow.rootViewController;

    while (topController.presentedViewController) {
        topController = topController.presentedViewController;
    }
    //NSLog(@"Top View is: %@",NSStringFromClass([topController class]));
    return topController;
}

你可以使用[viewController Class]方法找出一个viewController的类的类型。