http://blog.csdn.net/qq_25073253/article/details/73730249?locationNum=5&fps=1
https://groups.google.com/forum/#!topic/digits-users/FfeFp0MHQfQ
http://blog.csdn.net/c437yuyang/article/details/76686212
http://www.cnblogs.com/denny402/p/5082341.html