what would you use for effects (like error message, navigation etc) instead of StateFlow? Would just a broadcast channel be used or is that going to be deprecated?

We wrote our own

EventFlow

for that. It is like a StateFlow with respect that it is a hot stream of data, but it differs that it is state-less (a new collector will not receive the last value it had emitted). Think of a StateFlow like it could've been backed by a Conflated Broadcast Channel and of an EventFlow like it could've been backed by a rendezvous Channel.

ya thats basically exactly what im looking for. Is there a downside to using rendezvous channel directly?

You can emit a value outside of a coroutine scope context (suspend function) by calling

offer

instead of

send

. But you risk loosing an emission if no one is listening/collecting (but then it wouldn’t be a problem… 🙂 )

Oh ok. Then I'll probably just use a channel I guess

I have to back-track the “when non one is listening” a bit. Also, if a collector/listener is on a different thread and is too slow in handling an emitted event, it may get lost when using

offer

instead of

send

.

ah ok. it probably still works for something like an error message or navigation event though

E.g you (your producer) calls

channel.send(event)

in one background thread more than once in really quick succession. And your collector in the UI, on the Main thread (Main dispatcher), which should finish in 16ms, but is somehow a bit slower than the producer calling the

send

method for the 2nd time. Usually this is not a big issue, since Events are often used for navigation and two navigation events should not be emitted in such quick succession (faster than the UI can handle them).

You also could use consumable event approach with StateFlow, so emit special event object with event inside, which can be retrieved only once (consumed) We use this approach in RxJava too

Hmm Rx java has that built in with the publish subject

Yes, but we use this approach not because we missed publish subject, just because it's safer, someone have to dispatch event, so it's harder to lost it

But if you'd use a rendezvous Channel that is backing a (custom) EventFlow, emitting a value by calling

send

on that channel would not risk losing any events, even if the consumer's CoroutineScope is cancelled (eg UI detached), because if the consumer (collector) is detached no one is listening and the sender/producer will just suspend until a new collector arrives (UI re-attached).

Yes, but doesn’t allow have multiple subscribers