How to make autosave in a fragment on the back button?

Question

Android

There are two fragments in one list, the second is a form. When closing the form by Back, you need to save and so that the data in the list is updated.
Tried Observer. I connect it in Attach, I disconnect it in Detach. But something does not grow together and nothing is updated.

Answer 1

Is it correct?
If you think that is correct from the user's point of view, then look at
onStop
onPause
onBackPressed