activity 启动另一个 activity 相互的生命周期，非常重要！！！！！！！！！

The order of lifecycle callbacks is well defined, particularly when the two activities are in the same process (app) and one is starting the other. Here's the order of operations that occur when Activity A starts Activity B:

1. Activity A's onPause() method executes.
2. Activity B's onCreate(), onStart(), and onResume() methods execute in sequence. (Activity B now has user focus.)
3. Then, if Activity A is no longer visible on screen, its onStop() method executes.

This predictable sequence of lifecycle callbacks allows you to manage the transition of information from one activity to another.