first activity
onCreate()
onStart()
onResume()
onPause()
second Activity
onCreate()
onStrart()
onResume()
first Activity onStop() 仅在全遮盖
second Activity onPause()
first Activity
onRestart() 不需要重新创建 即不需调用 onCreate() 因为第一个Activity未被销毁掉
onStart()
onResume()
second Activity
onStop()
onDestroy()
