can anyone suggest any article/sample showing how JetpackCompose can be used with StateFlow?

# compose

[Daniele B]

can anyone suggest any article/sample showing how JetpackCompose can be used with StateFlow?

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

https://cs.android.com/androidx/platform/frameworks/support/+/androidx-master-dev:compose/compose-runtime/samples/src/main/java/androidx/compose/samples/FlowAdapterSamples.kt;l=26?q=StateFlow&sq=&ss=androidx

[Daniele B]

that’s very interesting! so is it that easy to make a component “listen” to a StateFlow?!

[Vinay Gaba]

Yeah pretty much! collectAsState converts it to a form that compose understands (state) and is able to listen to the stream seamlessly.

[Vinay Gaba]

recently played with it and added an example with comments here - https://github.com/vinaygaba/Learn-Jetpack-Compose-By-Example/blob/master/app/src/main/java/com/example/jetpackcompose/state/coroutine/CoroutineFlowActivity.kt

[Daniele B]

Wow! it’s really amazing! Thanks for showing it to me

[Daniele B]

I was looking for a simple example online, but I could not find it

[Daniele B]

did you have any chance to play with StateFlow and SwiftUI in a KotlinMultiplatform context?

[Daniele B]

I wish it was so simple too, but I doubt it 😄

[Vinay Gaba]

I’ve not dabbled with SwiftUI yet but it’s definitely something I will hopefully do at some point 😄

[Daniele B]

great! let’s keep in touch then, I will be working on a multiplatform project in the next months

[Vinay Gaba]

excited to see your progress!

[Daniele B]

thanks! 👍

[Daniele B]

you gave me a very clear starting point, I am very glad

[Daniele B]

Hi Vinay, I have a question about your sample. Is “initial” a special keyword?

[Daniele B]

is it specific of Flow?

[Vinay Gaba]

that’s just a named parameter to the collectAsState method.

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

https://developer.android.com/reference/kotlin/androidx/compose/package-summary#(kotlinx.coroutines.flow.Flow).collectAsState(androidx.compose.kotlinx.coroutines.flow.Flow.collectAsState.T,%20kotlin.coroutines.CoroutineContext)

[Daniele B]

perfect! that’s clear now

[Daniele B]

thanks!

[Vinay Gaba]

🙌🏼

[Daniele B]

@Vinay Gaba I actually realized you are using Flow instead of StateFlow. Is there a specific reason?

[Daniele B]

as far as I understand StateFlow is a hot flow, while Flow is a cold flow

[Daniele B]

which is the effect of using Flow instead of StateFlow inside a Composable?

[Daniele B]

I was reading that: “StateFlow only returns if the value has updated and doesn’t return the same value. In simpler terms, consider two values x and y where x is the value initially emitted and y is the value to be emitted. StateFlow makes sure, if (x == y) the do nothing but if (x !=y) then only emit the new value i.e. y in this case.”

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

As far as the consumer is concerned, the only difference between Flow and StateFlow is that you can ask a StateFlow for its current value without collecting it, and it will always immediately emit a value when collected.

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

That’s why the StateFlow.collectAsState() doesn’t require you to pass in an initial value, but Flow.collectAsState does.

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

as far as I understand StateFlow is a hot flow, while Flow is a cold flow

Not exactly. A Flow can be hot as well, since StateFlow is a subtype of Flow. The types don’t necessarily imply anything about their “temperature”.

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

Unlike Flow vs Channel, where Channel is always hot.

[Daniele B]

@Zach Klippenstein (he/him) [MOD] thanks for the explanation! it’s clear now