Is it possible to remember a value `Bitmap` for longer than

Question

Is it possible to remember a value `Bitmap` for longer than the usual `remember` but without using `rememberSaveable` Im basically putting my screen in the backstack for a few moments and upon return Id still like to be able to access the bitmap At the same time I dont want to cache it in a variable outside of composition skull

Zoltan Demant · Answer

This question can also be rephrased to How can I know when my composable is actually 100 leaving the composiiton without being part of the backstack

Alex · Answer

The typical solution would be a `ViewModel` but you could also create your own `remember` which stores the bitmap in the `nonconfigurationinstance`

Alex · Answer

May I ask why you dont want to ~store~ cache the bitmap outside of the composition

Zoltan Demant · Answer

Can you please elaborate on what you mean by `remember` that stores it in `nonconfigurationinstance` About storing it outside of composition gt I would have no way of knowing when to dispose it

Zoltan Demant · Answer

Also not using viewmodels in my project otherwise I think its the best or at least simplest solution to this

Pablichjenkov · Answer

To know when your Composable is leaving the composition 100 doesn t DisposableEffect work for this matter I would place a disposable effect in the screen you said will be put in the backstack for a moment then place some logs to see what happens when it is place in the backstack and presented again

Zoltan Demant · Answer

The DisposableEffect onDispose is called when the composable enters the backstack unfortunately

Zoltan Demant · Answer

And that makes sense its no longer called while its in the backstack smiley

Pablichjenkov · Answer

Got you unfortunately for your use case

Zoltan Demant · Answer

Ultimately I got it working with `rememberSaveable` I forgot that Bitmap was Parcelable Not sure if its the best solution but Im glad the Bitmap goes away when the composable does If anyone has any better solution still Id love to hear it

yschimke · Answer

Do you have any sort of scope similar to ActivityRetained or ViewModel in your app Or you are just using rememberSaveable to restore

Zoltan Demant · Answer

Yes its effectively similar to how viewmodels are scoped to navgraph destinations BUT this blur effect is a design system component

Alex · Answer

Saving the bitmap is usually not the best solution because the bitmap can easily exceed 1mb which is the limit for parcels of modern devices

Alex · Answer

But your comment gave me a nice idea for a good solution for you instead of saving the bitmap to a parcel you can create a remembersaveable that stores the bitmap in a cache file and saves the uri of that file to the parcel

Alex · Answer

In that way you will avoid the parcel size limitation because only the cache file path will be contained inside of the parcel

Zoltan Demant · Answer

When how would I remove the bitmap from the cache in that case

Alex · Answer

That s an interesting question let me check the api if there is something suitable

yschimke · Answer

Where does the bitmap come from originally an Image Loader library would handle this normally And take in a URL

Zoltan Demant · Answer

I m creating it from my composable similar to taking a screenshot of it

Zoltan Demant · Answer

Basically doing that and applying a blur to it then rendering it So it looks weird if it disappears momentarily when you navigate back to this screen

Zoltan Demant · Answer

Unfortunately I have not been able to find a solution to this yet Feel free to suggest if you have any ideas smiley `rememberSaveable` is the closest to a proper solution but as others have mentioned it will likely cause issues due to the size of the bitmaps

Zoltan Demant · Answer

I dont think this is possible to do with compose only disappointed I ended up involving my framework so basically caching the bitmap in a viewmodel of sorts It works as expected the bitmap is removed when the viewmodel leaves the backstack etc Its an okay workaround for now but ultimately I want to find a way to do this without involving the framework If anyone has any further ideas please let me know pray skin tone 4 Thanks for the discussions