IssueTracker

Component used: lifecycle-viewmodel-savedstate Version used: 2.3.0-alpha01

SavedStateHandle is currently the only mechanism for accessing saved instance state from a ViewModel. However, it currently forces you to only use objects that can be put in a Bundle since set() verifies the type of object immediately.

It would be nice if SavedStateHandle could also support lazy serialization of objects - namely, having some equivalent to being able to register a onSaveInstanceState() like callback.

It seems like this is precisely what something like SavedStateProvider could fill. You could registerSavedStateProvider() with a String key and a SavedStateProvider and the SavedStateHandle would be responsible for calling saveState() on each provider to fill in the Bundle for that key.

It would be the responsibility of the ViewModel for maintaining the non-bundable object outside of SavedStateHandle (i.e., having its own MutableLiveData) as well as in implementing the SavedStateProvider.

There'd need be some way to access the previously saved state - perhaps the underlying get() method would return a Bundle? indicating the previously saved state and/or registerSavedStateProvider() could return that same Bundle?.