Is there a way to "detach" a value from a `@Model`...

# compose

[mon]

Is there a way to "detach" a value from a @Model so that it stops getting updated when the field it is read from changes?

[Chuck Jazdzewski [G]]

I am uncertain what you are asking.

When an @Model changes the FrameManager (which will be renamed, probably to CompositionManager) will check if it was read from any compositions and schedule the function that read it to recompose (internally by invalidating the recompose scope created by the function when it called startRestartGroup()).

The value read from the @Model is not tracked after the read unless it, itself, is an @Model object.

[Leland Richardson [G]]

I think @mon is wondering whether or not you can have a mutable property on a model that won’t trigger recompositions when you read/write to it.

We don’t have an explicit mechanism for this, but it’s not hard to accomplish as is. @Model is a shallow transform, so it won’t transform nested objects.

class ValueHolder<T>(var value: T)

@Model MyModel {
  // x will cause recompositions
  var x = 0
  private val yHolder = ValueHolder(0)
  var y: Int
    get() = yHolder.value
    set(field) = yHolder.value = field
}

[Leland Richardson [G]]

Note that you can also just use mutableStateOf to have a single property that is “tracked”, and the rest of the class won’t be

class MyModel {
  var x by mutableStateOf(0)
  var y = 0
}

[Leland Richardson [G]]

similarly, if you had ValueHolder implement the property delegate operators, you could do the inverse as well:

@Model class MyModel {
  var x = 0
  var y by ValueHolder(0)
}

[mon]

Thank you, I think by mutableStateOf is what I need