Hello, how do i make this idea work : api.stream is reading a websocket, the idea is to update a var...

# compose

[Felipe Passos]

Hello, how do i make this idea work :
api.stream is reading a websocket, the idea is to update a variable every time it receives a websocket message.

Sem título.kt

[Se7eN]

You can use a lambda:

suspend fun updateState(api: Api, onRecieve: (String) -> Unit) {
    val notify =  Channel<String>()
    api.stream(notify)
    while(true) {
        onRecieve(notify.receive())
    }
}  

@SuppressLint("CoroutineCreationDuringComposition")
@Composable
fun SomeComposable(api: Api, locationViewModel: LocationViewModel = viewModel()) {
    var state by remember { mutableStateOf("") }
    val composableScope = rememberCoroutineScope()
    composableScope.launch {
        updateState(api, onRecieve = { state = it })
    }
}

[Felipe Passos]

This makes the api.stream goes on some loop and connect multiple times instead of one time and just reading

[Se7eN]

Oh yeah you need LaunchedEffect

[Felipe Passos]

What is this ?

[Se7eN]

https://developer.android.com/jetpack/compose/side-effects#launchedeffect

[Felipe Passos]

What do i use as a key?

[Felipe Passos]

Oh, get it

[Se7eN]

I guess you can use your api as the key since it will relaunch when your api changes

[Se7eN]

Also, shouldn't the updateState be in your view model?

[Felipe Passos]

Any idea why it prints "" then the real state value ?

Sem título.kt

[Se7eN]

Because the initial value of your state is an empty string

[Felipe Passos]

Any way to the variable only holds the newer value ?

[Felipe Passos]

I'm using the view model to store some coordinates that changes when the user click on a map

Sem_titulo.kt

[Se7eN]

You can make the state null initially or maybe use a flow

[Se7eN]

You can make another view model for your api stuff if you don't want it in the location view model

[Felipe Passos]

So a viewModel is better than a simple remember in this case?

[Se7eN]

From what I'm seeing, yes. It's always better to keep the UI separate

[Dominaezzz]

Should probably be fun updateState(api: Api): Flow<String> that returns a channelFlow { .... } . Then you can use collectAsState() .

[Felipe Passos]

What would be a snippet of this ? i never used a channelFlow before

[Dominaezzz]

fun updateState(api: Api): Flow<String> {
    return channelFlow<String> {
        api.stream(this)
        awaitClose { /* do closing things if needed */ }
    }
}

[Dominaezzz]

@SuppressLint("CoroutineCreationDuringComposition")
@Composable
fun SomeComposable(api: Api, locationViewModel: LocationViewModel = viewModel()) {
    val state by remember(api) { updateState(api) }.collectAsState("")
    // do stuff with state
}

[Felipe Passos]

I saw here that it is a experimental api, is this safe to use ?

[Dominaezzz]

It was stabilised in the latest release so don't worry about it.

[Felipe Passos]

Ok, thank you all !