https://blog.csdn.net/jdsjlzx/article/details/46860563 https://github.com/qibin0506/DropEditText
https://download.csdn.net/download/heiyelijie/6954347
https://blog.csdn.net/u014293306/article/details/52402537
http://yuxiatongzhi.iteye.com/blog/2067343
原文：https://www.cnblogs.com/genggeng/p/8900759.html