可以参考这篇文章
https://medium.com/@ali.muzaffar/which-context-should-i-use-in-android-e3133d00772c
Context
|— ContextWrapper
|— —Application
|— —ContextThemeWrapper
|— — — —Activity
|— —Service
|— — — IntentService
Application的Context对于Activity而言没有返回栈
Context一般用来access system level resources (getSystemSer
