I've been reading the source code of Compose and f...

# compose

[Julius Marozas]

I've been reading the source code of Compose and found that in the rxjava2 package the subscribeAsState function calls asState and it uses the onPreCommit hook. Why would the onCommit hook not work there? I don't really understand the use case of onPreCommit.

[Adam Powell]

The distinction is probably going away soon. The difference is that onCommit posts the event to happen "a bit later" rather than as we're actually applying the changes to the composition. The direction we're leaning in is that the current deferred onCommit behavior will go away and only the onPreCommit behavior will remain.

[Adam Powell]

so the reason this is using onPreCommit is just a minor latency and timing improvement over onCommit.

[Julius Marozas]

Oh, okay. So the reason they were made separate was
not to overwhelm compose with not as crucial events (and put those in onCommit)?

[Adam Powell]

no, the reason they were made separate is partially historical and had to do with whether it was risky or not to execute side effects of a composition while the process of applying them was still in progress, vs. after all of them have been completely applied.

[Adam Powell]

Some internal dispatching logic around this changed and the onPreCommit path is already "deferred" until after all tree changes happen, but it doesn't yield to a system handler/scheduler to do it, which avoids ordering questions and a small amount of latency.

[Julius Marozas]

Thanks for the detailed response!