Hello, we have a state object `CommonInput` in viewModel, which gets posted to StateFlow and then co...

# compose

[ildar.i [Android]]

Hello, we have a state object CommonInput in viewModel, which gets posted to StateFlow and then converted into a @Composable fun CommonInputDisplay in our Composable screen. CommonInput has a value param that gets converted to MutableState and used in TextField as value.
The problem is that once it has initialized, we can’t change TextField value by modifying state object from ViewModel anymore. How can we initiate a recomposition with a new value from viewModel by modifying CommonInput?

Untitled.cpp

[Filip Wiesner]

CommonInput::value could be a Compose State 🤷

[Filip Wiesner]

Something like

class CommonInput(
  val initialValue: String? = null
  ...
) {
  var value by mutableStateOf(initialalue)
    private set
}

[ildar.i [Android]]

I know, but can ViewModel be not aware of compose? Ideally it should just post new state and Compose screen just updates

[yschimke]

You could pass it in as a State<X> or lambda. But that feels wrong. Why not make it a val and pass in a new CommonInput instance. If you want to avoid work on recomposition, you could remember other things on the stable fields.

[Filip Wiesner]

Ideally it should just post new state and Compose screen just updates

Sure but in that case the CommonInput cannot have mutable properties and cannot mutate iteslf. ViewModel has to do that like yschmke suggests:

make it a val and pass in a new CommonInput instance

[yschimke]

Exactly. I think you are fighting compose by using mutable fields.

[ildar.i [Android]]

Right now even if I change all vars to val my screen doesn’t recompose after I post updated state to StateFlow. The values on ViewModel are new, but UI stays the same

[Filip Wiesner]

Try changing the CommonInput class to data class

[ildar.i [Android]]

No change as well with data class

[Filip Wiesner]

Can you show us how do you emit new values to your state flow and how do you collect it?

[ildar.i [Android]]

Untitled.txt

[ildar.i [Android]]

LaunchedEffect(item.value) {
    if (item.value.orEmpty() != inputText) inputText = item.value.orEmpty()
}

I added this after inputText initialization and it started to work properly. Is that a correct thing to do here?

[Filip Wiesner]

The inpuText should just be val inputText = item.value.orEmpty(). No need to create internal state

[ildar.i [Android]]

yeah, indeed) thank you!

[Filip Wiesner]

And your onValueChange should just call the VM to emit new state - single source of truth