Objective-c版本：

- (UIViewController *)appRootViewController
{
    UIViewController *appRootVC = [UIApplication sharedApplication].keyWindow.rootViewController;
    UIViewController *topVC = appRootVC;
    while (topVC.presentedViewController) {
        topVC = topVC.presentedViewController;
    }
    return topVC;
}

Swift版本：

func AppRootViewController() -> UIViewController? {
    var topVC = UIApplication.sharedApplication().keyWindow?.rootViewController
    while topVC?.presentedViewController != nil {
        topVC = topVC?.presentedViewController
    }
    return topVC?
}