获取屏幕当前最上层 Controller

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