Should the automatic recomposition feature of

@Model

be working in the current Compose code? I created this based on the

@Model

KDoc:

@Model
    data class AgreementViewState(var terms: Boolean = true, var privacy: Boolean = false) {
        val canProceed = terms && privacy
    }

    @Composable
    private fun Agreement() {
        Padding(8.dp) {
            val viewState = +model { AgreementViewState() }

            Column(mainAxisAlignment = MainAxisAlignment.Start, crossAxisAlignment = CrossAxisAlignment.Start) {
                Row(mainAxisAlignment = MainAxisAlignment.Start) {
                    Checkbox(
                        checked = viewState.terms,
                        onCheckedChange = { viewState.terms = it }
                    )
                    Text(text = "I agree to the terms and conditions")
                }
                Row(mainAxisAlignment = MainAxisAlignment.Start) {
                    Checkbox(
                        checked = viewState.privacy,
                        onCheckedChange = { viewState.privacy = it }
                    )
                    Text(text = "I agree to the privacy policy")
                }
                Text(text = if (viewState.canProceed) "You may proceed" else "Please indicate your agreement")
            }
        }
    }

The initial state works (the top

Checkbox

is checked). And via logging I can confirm that my

onCheckedChange

lambdas are being called. However, the UI is not being recomposed as I update the

AgreementViewState

, so the checkboxes and text remain fixed. By contrast, this works with automatic recomposition as I update the `checkboxState`:

@Composable
    private fun SimpleCheckbox() {
        Padding(8.dp) {
            val checkboxState = +state { true }

            Checkbox(
                checked = checkboxState.value,
                onCheckedChange = { checkboxState.value = it }
            )
        }
    }

I'm trying to determine if there's something that I'm doing wrong or if this is just a current limitation. Thanks!

Hey! Is this @model class defined as nested or it's top level?

ah, it's nested -- let me try moving it

No problem, I can imagine how annoying this little problems might be. Wild guess on the crashes: if there's "not in a frame" error -- it means that you're reading or writing @model fields from non-ui thread, which we for now don't fully support.

No, I was getting an NPE-equivalent about an

r

value not being set. Then, I mistakenly tried cleaning the project, in case I had lingering code generated from the previous (nested) location. That completely broke the project, so now I need to try to convince the Compose custom Studio build to work again. 😣

Looking at the code, it appears

canProceed

should be a getter (or extension property).

I can confirm that both a function and an extension property work. I filed https://issuetracker.google.com/issues/139653744 to document the derived property not working. Let me know if you think more stuff is needed in that issue. Many thanks!

Also declaring it as

var

works fine for me

Ummm... good point. I'm used to thinking of immutable view states, where

canProceed

would be a derived property.

@Model

is all about the mutability, though.

Not saying a crash is expected, but how can it be updated?

Text(text = if (viewState.canProceed) "You may proceed" else "Please indicate your agreement")

will never print

You may proceed

if you have

canProceed

as a val initialized by default as false