Are there other ways to cause recompositions other than changing UI state backed by `State`?

# compose-android

[Lucas Kivi]

Are there other ways to cause recompositions other than changing UI state backed by State?

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

Yes, to name a few:
• your caller is recomposed and passes you some new values
• a static composition local is changed
• I think maybe if you’re in a movableContent and moved? Not sure though
But compose doesn’t make any guarantees about all the reasons a recomposition could happen, so even if you had an exhaustive list of reasons right now, it could change in the future.

[Lucas Kivi]

Thank you for your response! I want to keep trying to poke holes in this.
• In a purely compose world, the caller would be recomposed only when State changes too, right?
• the static composition local would only be altered in a composition or recomposition, right? Which means in a purely compose world, State would have to change too, right? But State might change way up in the UI hierarchy and therefore the updated static composition local would really be the cause of the recompositions in the child composables.
• does moving movableContent change some State ? I didn’t look too far into the implementation.

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

Oh I misread your question, I thought you meant a state read by the composable in question. I guess technically all changes happen due to a snapshot state change somewhere? I think even when you call setContent on a ComposeView it just updates a state object.

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

Ok this is maybe one: the size of the host view could change based on some external trigger, and then some layout inside the composition could choose to subcompose something else based on this new constraints

[Lucas Kivi]

whooooaaa.. that is an interesting one. But for all intents and purposes, all changes are due to a snapshot state change somewhere. Very good. I am writing an article and was going to claim that all recompositions can be sourced to some State update. It seems like that is mostly true.

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

Don’t quote me on that though. I’d need to comb through the source to verify. And more importantly, it’s not a guarantee made by compose.

[Lucas Kivi]

Right I am just making a general claim about how recompositions occur and discussing how you can minimize them using some simple techniques

[Lucas Kivi]

Thank you again for you time, Mr. Sir.

[shikasd]

It is generally true, recomposition is driven by state changes. There are a few notable exceptions like subcompose layout, which Zach outlined above, but 99% of changes are driven by state.

[Lucas Kivi]

Thank you! Love you guys ❤️