The model is read-only by default. To make it read-write, you must subclass it and reimplement
setData() and flags().
尝试edit半天，最后在文档中发现这句话。哎，"edit: editing failed"问题终于解决了！
http://www.cnblogs.com/codingmylife/archive/2010/04/25/1719913.html