activity 工作流

https://blog.csdn.net/cs_hnu_scw/article/details/79059965

https://blog.csdn.net/xnf1991/article/details/52610277

这个写的比较细

https://blog.csdn.net/yerenyuan_pku/article/details/71307305

这个也不错

https://blog.csdn.net/yerenyuan_pku/article/details/71307305