What isn't working?

# compose

[brandonmcansh]

What isn't working?

[nglauber]

Both:
1. The delayed welcome message
2. The counter when the Button is pressed.

[nglauber]

Ok. I found a solution…

val count = remember { mutableStateOf(0) }
val welcomeMsg = remember { mutableStateOf("") }

Now I need an explanation 😄

[gildor]

Because you recreated mutableStateOf(0) on every composition

[gildor]

if you want state survive recomposition, use remember

[gildor]

See https://kotlinlang.slack.com/archives/CJLTWPH7S/p1592953325034000

[nglauber]

thanks @gildor. I saw this discussion and once state is deprecated, I thought the mutableStateOf will work as the same way.
Now makes sense 😉

[gildor]

Have you tried to apply auto fix for state?

[nglauber]

What’s that? Is it a AS feature? 🤔

[gildor]

IntelliJ + Kotlin Plugin

[nglauber]

No I din’t 😩

[gildor]

https://stackoverflow.com/questions/52202810/how-does-deprecated-replacewith-work-for-kotlin-in-intellij

[nglauber]

Is there another way to simulate the needs of remember ?

[gildor]

what do you mean “simulate” it?

[nglauber]

I mean a simple example where remember is required.

[nglauber]

Maybe I need to understand the concept of “recomposition”. I thought that “recomposition = composable is updated after the state changes”. But I’m clearly wrong

[gildor]

see, you should understand that any change which cause recomposition (such as state change) will call your compose function again

[gildor]

if you see on your code, you will see that without remember it means that`count` and welcomeMsg will bew set to default value

[gildor]

to avoid this, save this internal state of composable, you can use remember, which saves state, and init default value only first access

[nglauber]

I got that. but why do I need the remember when I’m using that launch and I don’t need it when I simply change the state.

[nglauber]

I both cases I’m changing the state of the composable and (in theory) the function is called again.

[gildor]

change state where?

[gildor]

a side note, you don’t need withContext around delay

[nglauber]

I know… It was just to simulate an IO operation 🙂

[gildor]

what do you mean that you don’t need remember there, isn’t your coroutine changes mutable state?

[nglauber]

Now the thing is more weird… this example is working 😄

@Composable
fun Demo10() {
    val scope = rememberCoroutineScope()
    Log.d("NGVL", "Here")
    val state = mutableStateOf(0)
    Button(
        onClick = {
            scope.launch {
                withContext(<http://Dispatchers.IO|Dispatchers.IO>) {
                    delay(1_000)
                }
                state.value = state.value + 1
            }
        },
        content = {
            Text(text = "Click ${state.value}")
        }
    )
}

[nglauber]

without remember 😕

[gildor]

it’s just avoids recomposition, if something else will cause it, you will lost your state

[gildor]

not really sure honestly

[gildor]

but any external change also may cause your Demo10 to recompose

[romainguy]

state{} is just remember{mutableStateOf()} btw

[nglauber]

but state is deprecated 😕

[romainguy]

Yes

[gildor]

yes, so you have to use remember { mutableStateOf() }

[gildor]

Read doc of state function, it has pretty good explanation

[nglauber]

so why my last snippet is working without the remember? 😕

[gildor]

Probably because it causes recomposition of Button + Text only

[nglauber]

yeah… I guess so…

[gildor]

It acutally recomposes only Text, not even Button. This state it used only there