如何在ios 8中设置键盘的alpha

Question

我使用ios8的键盘扩展编码，当我使用下面的代码时，它不能正常工作，有人可以帮助我吗？

   self.view.backgroundColor = UIColor.clearColor() //it became gray
   self.view.alpha = 0.1 //it made all the view on keyboard become transparent