Has anyone encountered data loss for state variabl...

# compose-android

[Alexandru Gheorghe]

Has anyone encountered data loss for state variables on a physical device? I used my phone with other apps and, upon resuming to the app in development, it correctly showed the right screen that was previously opened, however, all data was lost and the app was rendered unusable. It seems ViewModel mutableStateOf(...) variables were reset to default, initial(ized), values. This is the first time it ever happened to me. Any clues on how to address it without introducing init in ViewModels?

[Stylianos Gakis]

You just experienced what process death looks like. This is a very normal thing to happen, and it happens all the time. It's the entire reason why the architecture guides always talk about working with a single source of truth, using your persistent data layer as your SSOT etc.
Here are some relevant links.

https://developer.android.com/topic/libraries/architecture/saving-states#local
https://developer.android.com/guide/topics/resources/runtime-changes#user-expectations

[Timo Drick]

You also may look at the lifecycle of view models. They do not live for ever.

[Stylianos Gakis]

Indeed, a process death does mean that you will get a whole new instance of your ViewModel. Which is exactly why you saw the mutable states "re-initialize" as you said yourself.
What would persist is if you saved anything in the SavedStateHandle (hence the name).

[Ian Lake]

Note there are a number of savedStateHandle.saveable extensions available for backing your MutableState with the SavedStateHandle so that it can survive configuration change - it uses the same Saver APIs that rememberSaveable uses: https://developer.android.com/reference/kotlin/androidx/lifecycle/viewmodel/compose/package-summary?hl=en#extension-functions