UIApplication+TopVC.swift

extension UIApplication {
    
    static var topViewController: UIViewController? {
        var topVC = UIApplication.sharedApplication().keyWindow?.rootViewController
        
        if let tabController = rootTabBarController {
            topVC = tabController.selectedViewController
        }
        
        while(topVC?.presentedViewController != nil) {
            topVC = topVC!.presentedViewController
        }
        
        if let navController = topVC as? UINavigationController {
            topVC = navController.visibleViewController
        }
        
        return topVC
    }

}