How to you keep the value of `state { ... }` across configuration changes?

# compose

[Archie]

How to you keep the value of state { ... } across configuration changes?

[Zach Klippenstein (he/him) [MOD]]

I think using the saved state registry should help, i.e. use savedInstanceState {} instead of state {}

[matvei]

Substitute state {} for savedInstanceState {}

[matvei]

Oh Zach is so fast 😅

[Archie]

ohh i see thank you :D

[Sinan Kozak]

why are those two different thing? Is there a benefit choosing state over savedInstanceState?

[Ricardo C.]

savedInstanceState has the usual restrictions. You can’t put big objects there and you’ll have to parcel/serialize them

[Adam Powell]

Once you get into the discussion of, "yes but what about ViewModels? Those don't need to parcel!" you also get into the property of config changes where you commonly rearrange the UI shape in those different configurations and the API has to again account for different things. Compose doesn't know which parts of a very different composition shape are semantically equivalent and how to key them without your help.

[Adam Powell]

So yes, parts of this are WIP 🙂

[Sinan Kozak]

A different question, could compose has its own rotation state independent from activity? Is this possible, having portrait locked activity and letting compose to handle rotation?

[Adam Powell]

Camera apps more or less do that but it would have a lot of side effects affecting a lot of view interop. There's nothing stopping one from trying it, really. If you're looking primarily to preserve state, marking the host activity as handling its own configuration changes is probably a less disruptive path.

[Adam Powell]

(and it's also worth noting that the activity configuration signals to do the camera-style thing are quite new in terms of which API level they were introduced in, if I recall)

[Adam Powell]

It would, however, open the door to doing some neat things with transition animations

[Sinan Kozak]

I will definitely experiment with transition for this, Just to check if having smooth rotation is possible 😄

[Adam Powell]

aha, thanks @Ian Lake for finding the other magic flag: https://developer.android.com/reference/android/view/WindowManager.LayoutParams#ROTATION_ANIMATION_SEAMLESS