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?}