如果根控制器是一个导航控制器，找到顶部可见控制器的正确方法是:

UIViewController *rootVC = [[UIApplication sharedApplication] keyWindow].rootViewController;
if ([rootVC respondsToSelector:@selector(visibleViewController)])
{
    UIViewController *topVC = [(UINavigationController *)rootVC visibleViewController];
    // do your thing with topVC
}

以下是UINavigationController.h的节选:

@property(nonatomic,readonly,retain) UIViewController *topViewController; // The top view controller on the stack.
@property(nonatomic,readonly,retain) UIViewController *visibleViewController; // Return modal view controller if it exists. Otherwise the top view controller.

另一个Swift解决方案

func topController() -> UIViewController? {

    // recursive follow
    func follow(from:UIViewController?) -> UIViewController? {
        if let to = (from as? UITabBarController)?.selectedViewController {
            return follow(to)
        } else if let to = (from as? UINavigationController)?.visibleViewController {
            return follow(to)
        } else if let to = from?.presentedViewController {
            return follow(to)
        }
        return from
    }

    let root = UIApplication.sharedApplication().keyWindow?.rootViewController

    return follow(root)

}

I am thinking that perhaps one thing is being overlooked here. Perhaps it is better to pass the parent viewController into the function that is using the viewController. If you are fishing around in the view hierarchy to find the top view controller that it is probably violating separation of the Model layer and UI layer and is a code smell. Just pointing this out, I did the same, then realized it was much simpler just to pass it in to function, by having the model operation return to the UI layer where I have a reference to the view controller.

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
    }
}

另一个解决方案依赖于responder链，它可能工作，也可能不工作，这取决于第一个responder是什么:

获取第一个响应器。 获取与第一个responder相关联的UIViewController。

示例伪代码:

+ (UIViewController *)currentViewController {
    UIView *firstResponder = [self firstResponder]; // from the first link above, but not guaranteed to return a UIView, so this should be handled more appropriately.
    UIViewController *viewController = [firstResponder viewController]; // from the second link above
    return viewController;
}

你可以通过使用找到最顶层视图控制器

NSArray *arrViewControllers=[[self navigationController] viewControllers];
UIViewController *topMostViewController=(UIViewController *)[arrViewControllers objectAtIndex:[arrViewControllers count]-1];