android - When is the savedInstanceState bundle actually used?

Question

Does anyone know of an exhaustive list of when the savedInstanceState bundle will be used in an activity?

I know it's used when the device orientation changes. However, it doesn't seem to be used when the user force closes the app from the Android settings, but this might be due to something in my code.

What other cases are there?

To be clear, by "used" I mean when onCreate() is called, the savedInstanceState bundle is not null and contains the data I passed into it the last time onSaveInstanceState() was called.

Answer 1

It's used when the Activity is forcefully terminated by the OS (ex: when your Activity is in the background and another task needs resources). When this happens, onSaveInstanceState(Bundle outstate) will be called and it's up to your app to add any state data you want to save in outstate.

When the user resumes your Activity, onCreate(Bundle savedInstanceState) gets called and savedInstanceState will be non-null if your Activity was terminated in a scenario described above. Your app can then grab the data from savedInstanceState and regenerate your Activity's state to how it was when the user last saw it.

Basically in onCreate, when savedInstanceState is null, then it means this is a 'fresh' launch of your Activity. And when it's non-null (if your app saved the data in onSaveInstanceState(...), it means the Activity state needs to be recreated.