CODEWITHSUNDEEP
androidkotlinandroid-jetpack-compose
Elye
Elye

Reputation: 60081

How can I pass a delegated mutableVariable to a Compose function?

I'm trying to pass the MutableState variable over another function. The below is all good. But I don't like the myMutableState.value

@Composable
fun Func() {
    val myMutableState = remember { mutableStateOf(true) }
    Column {
        AnotherFunc(mutableValue = myMutableState)
        Text(if (myMutableState.value) "Stop" else "Start")
    }
}

@Composable
fun AnotherFunc(mutableValue: MutableState<Boolean>) {
}

So I decided to use val myMutableState by remember { mutableStateOf(true) }, as shown below. I no longer need to use myMutableState.value as shown below.

Unfortunately, the below won't compile. This is because I cannot pass it over the function AnotherFunc(mutableValue = myMutableState)

@Composable
fun Func() {
    val myMutableState by remember { mutableStateOf(true) }
    Column {
        AnotherFunc(mutableValue = myMutableState) // Error here
        Text(if (myMutableState) "Stop" else "Start")
    }
}

@Composable
fun AnotherFunc(mutableValue: MutableState<Boolean>) {
}

How can I still use by and still able to pass the MutableState over the function?

Upvotes: 9

Views: 7561

Answers (3)

ultrastal
ultrastal

Reputation: 1

by and remember don't have to be used together, you can split into 2 statements and extract the MutableState variable.

val myMutableState = remember { mutableStateOf(true) }
var myValue by myMutableState

@Composable
fun Func() {
    val myMutableState = remember { mutableStateOf(true) }
    var myValue by myMutableState
    Column {
        AnotherFunc(myMutableState)
        Text(if (myValue) "Stop" else "Start")
    }
}

@Composable
fun AnotherFunc(mutableState: MutableState<Boolean>) {
}

Upvotes: 0

Aaron Liu
Aaron Liu

Reputation: 761

While Johann's solution works for OP's specific scenario, to be able to assign the passed parameter another value, you'd need a Lambda function for each change, like this:

@Composable
fun AnotherFunc(mutableValue: Boolean, onMutableValueChange: (Boolean) -> Unit){
    onMutableValueChange(false) // myMutableState would now also be false
}

@Composable
fun Func() {
    val myMutableState by remember { mutableStateOf(true) }
    Column {
        AnotherFunc(mutableValue = myMutableState, onMutableValueChange = {myMutableState = it})
    }
}

(Boolean) -> Unit means a function that accepts a Boolean as a parameter and doesn't have a return value. Simply pass a lambda function to change mutableValue as seen in the example above, and call it in AnotherFunc whenever you need to change mutableValue.

Upvotes: 8

Johann
Johann

Reputation: 29867

=-0987our composable function should just take a boolean:

@Composable
fun AnotherFunc(mutableValue: Boolean) {
}

Not sure why your composable function (AnotherFun) needs to have a mutable state. The calling function (Fun) will automatically recompose when the value changes, triggering recomposition of AnotherFun.

Upvotes: 2

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