Find the topmost view controller

UIViewController+Topmost.h

//
//  UIViewController+Topmost.h
//
//  Created by Yiming Tang on 13-10-14.
//  Copyright (c) 2013 Yiming Tang. All rights reserved.
//

@interface UIViewController (Topmost)

+ (UIViewController *)topmostViewController;
+ (UIViewController *)topViewControllerWithRootViewController:(UIViewController *)rootViewController;

@end

UIViewController+Topmost.m

//
//  UIViewController+Topmost.m
//
//  Created by Yiming Tang on 13-10-14.
//  Copyright (c) 2013 Yiming Tang. All rights reserved.
//

#import "UIViewController+Topmost.h"

@implementation UIViewController (Topmost)

+ (UIViewController *)topmostViewController
{
    UIViewController *rootViewController = [UIApplication sharedApplication].keyWindow.rootViewController;
	return [self topViewControllerWithRootViewController:rootViewController];
}


+ (UIViewController *)topViewControllerWithRootViewController:(UIViewController *)rootViewController
{
    if ([rootViewController isKindOfClass:[UITabBarController class]]) {
        UITabBarController *tabBarController = (UITabBarController *)rootViewController;
        return [self topViewControllerWithRootViewController:tabBarController.selectedViewController];
    }
    else if ([rootViewController isKindOfClass:[UINavigationController class]]) {
        UINavigationController *navigationController = (UINavigationController *)rootViewController;
        return [self topViewControllerWithRootViewController:navigationController.visibleViewController];
    }
    else if (rootViewController.presentedViewController) {
        UIViewController *presentedViewController = rootViewController.presentedViewController;
        return [self topViewControllerWithRootViewController:presentedViewController];
    }
    else {
        return rootViewController;
    }
}

@end