这是对Eric的回答的改进:

UIViewController *_topMostController(UIViewController *cont) {
    UIViewController *topController = cont;

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

    if ([topController isKindOfClass:[UINavigationController class]]) {
        UIViewController *visible = ((UINavigationController *)topController).visibleViewController;
        if (visible) {
            topController = visible;
        }
    }

    return (topController != cont ? topController : nil);
}

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

    UIViewController *next = nil;

    while ((next = _topMostController(topController)) != nil) {
        topController = next;
    }

    return topController;
}

UIViewController *cont是一个辅助函数。

现在你所需要做的就是调用topMostController()和最顶端的UIViewController应该被返回!

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。

@implementation UIWindow (Extensions)

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

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

    return topController;
}

@end

使用下面的扩展抓取当前可见的UIViewController。适用于Swift 4.0及更高版本

Swift 4.0及以上版本:

extension UIApplication {
    
    class func topViewController(_ viewController: UIViewController? = UIApplication.shared.keyWindow?.rootViewController) -> UIViewController? {
        if let nav = viewController as? UINavigationController {
            return topViewController(nav.visibleViewController)
        }
        if let tab = viewController as? UITabBarController {
            if let selected = tab.selectedViewController {
                return topViewController(selected)
            }
        }
        if let presented = viewController?.presentedViewController {
            return topViewController(presented)
        }
        return viewController
    }
}

如何使用?

let objViewcontroller = UIApplication.topViewController()

另一个Swift解决方案

extension UIViewController {
    static var topmostViewController: UIViewController? {
        return UIApplication.sharedApplication().keyWindow?.topmostViewController
    }

    var topmostViewController: UIViewController? {
        return presentedViewController?.topmostViewController ?? self
    }
}

extension UINavigationController {
    override var topmostViewController: UIViewController? {
        return visibleViewController?.topmostViewController
    }
}

extension UITabBarController {
    override var topmostViewController: UIViewController? {
        return selectedViewController?.topmostViewController
    }
}

extension UIWindow {
    var topmostViewController: UIViewController? {
        return rootViewController?.topmostViewController
    }
}

斯威夫特5

试试这个

let topVisibleVC = UIApplication.shared.keyWindow?.rootViewController?.visibleViewController