Composable AndroidView update block is run on every key press

[jonnyandrew]

Problem

The update block of the composable AndroidView is run on every key press, whereas it should only run when a variable used inside the block is changed.

This block is supposed to run any time the style or callbacks are changed and isn't optimised to be run very frequently.

• Version 2.14.1 is not affected.
• Version 2.15.0 is affected.
• The main branch works around the issue to reduce performance impact (see [Android] Add support for mentions to the Compose library #854 (comment)) but the AndroidView still recomposed on every key press.

Proposed solution

Workaround implemented in #854

No solution is known.

[jmartinesp]

I think this is actually working as expected (although we didn't expect it to work like that 😅 ): looking at the source code, we can see the update lambda will only be called when the lambda instance changes, and this can happen in 2 scenarios:

1. Any variable captured in the lambda changes.
2. A recomposition of the parent composable.

By using a remember block we can cache the lambda using some keys (in this case, the captured arguments) and reuse it even if the parent composable is recomposed, instead of getting a new lamda.

As for why there were different behaviours after a clean build and an incremental one, I have no idea. It might be a compiler bug.

[jonnyandrew]

the update lambda will be called on a recomposition of the parent composable.

I thought the update block should only run again when one of the variables inside it changes, not whenever the parent recomposes. I created a small sample to test it and it seems to be working in this way. Can you let me know if I misunderstood something here?

[jmartinesp]

My theory was the AndroidView would be recomposed when anything captured in the onFactory lambda changed too, and this would in turn recompose the update lambda, but that wasn't the case after some quick testing, so it seems like I was wrong.

[jonnyandrew]

With Android Studio Hedgehog we're able to debug the reasons for recomposition and it looks to be caused by the onError passed from the sample app:

The only difference seems to be that we're passing a function reference. Replacing it with a lambda seems to make the issue go away but I have no idea why.