[FIXED] Remember mutableStateOf custom class in Android Compose

Issue

I created a android compose component and to avoid multiple params, it takes only one parameter : an object

Here is my component :

@Composable
fun ValidationButton(validationButtonModel: ValidationButtonModel)

My object :

import android.os.Parcelable
import kotlinx.parcelize.Parcelize

@Parcelize
data class ValidationButtonModel(
    var title: Int,
    var contentDescription: Int,
    var rfidReadingStarted: Boolean,
    var progression: Float,
    var read: Int,
    var expected: Int,
) : Parcelable

Here is how i define it to compose for being remember between recomposition AND being a state (launch recomposition when change) :

val validationButtonModelState by rememberSaveable() {
        mutableStateOf(
            ValidationButtonModel(
                R.string.common_validate,
                R.string.common_contentDescription,
                true,
                0.1f,
                7,
                10
            )
        )
    }

But if i try to update it with for example this :

ValidationButton(
                    validationButtonModelState,
                )

Button(onClick = 
          {
                 validationButtonModelState.rfidReadingStarted = true
                 if (validationButtonModelState.progression < 1.0f) {
                    validationButtonModelState.progression += 0.1f
                    validationButtonModelState.read += 1
                 }
          }, content = {
              Text("INCREMENT")
            })

There is no re composition.

I try to add a Saver but doesn't work too :

val validationButtonModelSaver = listSaver<ValidationButtonModel, Any>(
    save = { listOf(it.rfidReadingStarted, it.read, it.progression, it.expected, it.title, it.contentDescription) },
    restore = { ValidationButtonModel(rfidReadingStarted = it[0] as Boolean, read = it[1] as Int, progression = it[2] as Float, expected = it[4] as Int, title = it[5] as Int, contentDescription = it[6] as Int)}
)

val validationButtonModelState by rememberSaveable(validationButtonModelSaver) {
        mutableStateOf(
            ValidationButtonModel(
                R.string.common_validate,
                R.string.common_contentDescription,
                true,
                0.1f,
                7,
                10
            )
        )
    }

Am i missing something ? Following this : https://developer.android.com/jetpack/compose/state#parcelize It should works

Solution

If you only change the fields inside your model, mutableStateOf(ModValidationButtonModel) it won't work, as you are still updating your old instance. You need to pass in a new instance of your model effectively.

try

validationButtonModelState = ModValidationButtonModel()

or since it is a data class you can also do

validationButtonModelState = validationButtonModelState.copy(
    read = validationButtonModelState.read+1
)

Answered By - AagitoEx
Answer Checked By - Dawn Plyler (JavaFixing Volunteer)