一 介绍
Activity是android中使用最为频繁的组件，在官方文档中是这样描述的：An activity is a single, focused thing that the user can do. Almost all activities interact with the user, so the Activity class takes care of creating a window for you in which you can place your UI with setContentView(View). Activity是android中使用最为频繁的组件，在官方文档中是这样描述的：An act
