http://hi.baidu.com/mapleelf/blog/item/717b87994f79260b6e068cb8.html 转载一片文章做例子
自己加了例子.
http://topic.csdn.net/t/20041110/08/3537882.html
http://hi.baidu.com/hibydu/blog/item/6569bb3d72ae1102bba16747.html
http://hi.baidu.com/lsl_322/blog/item/834b08627e8942680c33fa9d.html
