Hey guys, I am working on changing background color of button. I want to know my example is good to ...

# compose

[KotlinLeaner]

Hey guys, I am working on changing background color of button. I want to know my example is good to use simple business logic in viewmodel with LaunchEffect . If there is any problem or better way please guide me on this. Thanks

[KotlinLeaner]

@Composable
fun ItemColorStateful() {
    var index by remember { mutableStateOf(-1) }
    val vm = koinViewModel<ColorViewModel>()
    LaunchedEffect(key1 = index) {
        vm.changeBackgroundColor(index)
    }
    Column(modifier = Modifier.fillMaxSize()) {
        Text(text = "Different Color")
        ButtonScopeStateless(
            index = index,
            onIndexChange = {
                index = it
            },
            backgroundColor = vm.backgroundColor
        )
    }
}

class ColorViewModel : BaseViewModel() {
    var backgroundColor by mutableStateOf(Color.Blue)

    fun changeBackgroundColor(index: Int) {
        backgroundColor = if (index != -1) {
            Color.Gray
        } else {
            Color.Blue
        }
    }
}

@Composable
fun ButtonScopeStateless(
    index: Int,
    onIndexChange: (Int) -> Unit,
    backgroundColor: Color,
) {
    Button(
        colors = ButtonDefaults.buttonColors(backgroundColor = backgroundColor),
        onClick = { onIndexChange(index + 1) }
    ) {
        Text(text = "Click Me $index")
    }
}

[KotlinLeaner]

My main goal is to avoid business logic in Composable function.

[Lilly]

Your approach makes only sense if you want to do something else with backgroundColor except simply changing its value

[KotlinLeaner]

yes i'll change with different colors with specfic number

[Lilly]

If you dont need backgroundColor outside of Compose, you can set value of index directly and Compose will automatically recompose the related components since you have defined you index as mutableStateOf

[KotlinLeaner]

How can I set the background color? Sorry I didn't get it. Can you please provide me example?

[Lilly]

What you are doing is correct, but you dont have to involve a viewmodel if you don't need backgroundColor outside of Compose scope

[KotlinLeaner]

Yes I don't need backgroundColor outside of compose. I used viewmodel because It can be used for unit testing. Composable functions are not testable.

[KotlinLeaner]

In my mentor project, testing is mandatory. I cannot find code coverage for composable stuffs. So that's why I moved to all business logic to viewmodel

[Lilly]

If you just want to demonstrate how to extract business logic, then it's done properly

[KotlinLeaner]

Thank you for your guidance. It clears my doubts.