Hey all - I've got an issue that I don't fully understand with MutableStateFlow not triggering a re-...

# compose

[Eric Boggs]

Hey all - I've got an issue that I don't fully understand with MutableStateFlow not triggering a re-compose when a deeply nested value changes. Basically, radio buttons set their value based on their status in state. When one is pressed, it toggles its value in state. Ideally, this should trigger a recompose but it doesn't. Made a little repro here if someone has any thoughts. https://github.com/boggsey/stateflow-test

[Eric Boggs]

It feels like I'm fundamentally not understanding something about Lists or about how Stateflow subscribes

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

I think your main problem is here: map just returns a new list with the result of the map function, so if you’re not assigning the returned value to anything it’s effectively a no-op.

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

I don’t understand what problem that deepCopy is trying to solve.

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

I think a better approach to selection would be for your view model to expose a selectedId property, which your composable could then compare to each article ID. That way you don’t need to walk the entire list in your view model every time the selection changes, and it means that if only the selection changes then only the two rows that actually had their selection state change need to recompose.

[Alex Vanyo]

The main issue I see is the var isSelected: Boolean in your Tag class.

This means that you have a mutable object inside an observable type, and the observable type has no way of knowing when the mutable object changes.

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

Oh i missed that, yea that’s no good either.

[Eric Boggs]

Ok, this is all helpful. I'm new to Kotlin and Android, so still figuring it all out. Regarding deepCopy, I wasn't sure how to push a deeply nested change as something that would trigger StateFlow to recognize the change

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

I wasn’t sure how to push a deeply nested change as something that would trigger StateFlow to recognize the change

As long as the equals method returns false, that will happen.

[Eric Boggs]

Thanks all! This sent me down the right path. Appreciate the help!