Setting a key/value on a `SavedStateHandle` within...

# android

[jeff]

Setting a key/value on a SavedStateHandle within a (Fragment's) ViewModel's onCleared() does not appear to take effect (i.e. survive activity death). Setting it prior to onCleared() e.g. in init {} does successfully persist. Is that expected? I don't see that behavior documented anywhere, other than that onCleared comes after onDestroy.

[Ian Lake]

onCleared() means that ViewModel is never, ever coming back. There's no state saved for things never coming back

[jeff]

onCleared() is called if the activity is killed but may be resumed later via savedInstanceState. That specific instance of the viewmodel isn't coming back, but the data in SavedStateHandle does.

[jeff]

Granted I'm doing this from a Fragment not an Activity, so maybe there's some nuance I'm missing there, but:
1. I have a ViewModel accessed from my Fragment via by viewModels()
2. that ViewModel injects a SavedStateHandle
3. I call set() on that SavedStateHandle either in A) init{} or B) onCleared()
4. Developer Settings -> don't keep activities is ON
5. Minimize app -> Activity destroyed
6. Return to app -> SavedStateHandle DOES contain my data in the case of A) and does NOT in the case of B)

[Ian Lake]

Yeah, onCleared() is never going to work for your use case, since the state is saved at the activity level (which percolates down to every fragment and every ViewModel) before/right after onStop() (depending on your API level), which is well before onCleared() is called

[Ian Lake]

Lifecycle 2.3 lets you just-in-time save data into your saved state, which would be the very last moment of time that saving is possible: https://stackoverflow.com/a/62800312/1676363

[jeff]

Thanks! I'll check that out.