How to retrieve the current displayed viewcontroller

gistfile1.m

//
// how to retrieve the current displayed viewcontroller
//
+ (UIViewController*)topMostController
{
    UIViewController *topController = [[UIApplication sharedApplication] keyWindow].rootViewController;
    while (topController.presentedViewController) {
        topController = topController.presentedViewController;
    }
    
    return topController;
}