hi all. I’m still grasping thinking in Compose, a...

# compose

[james]

hi all. I’m still grasping thinking in Compose, and I’m wondering if someone can guide me on the “correct” way to do this in the world of Compose.

I have a parent screen which holds some master context (let’s say someParentId), and that screen is made up of some child Composables, and those Composables each have their own ViewModels. I would like to re-initialize those child ViewModels when someParentId changes, so that they re-load their data (and in turn recompose whatever is required)

if I completely blow away the child ViewModels when someParentId changes and construct new ones, the corresponding UI must be recomposed every time, right? and that would be a very inefficient way to do it?

so does this mean that the correct way would be to have ParentViewModel hold a reference to ChildA ViewModel and ChildB ViewModel, and when someParentId changes I can just get my existing child ViewModel references, and tell them to fetch the relevant new data?
(hastily drawn pic for reference in case the relationships were unclear)

[Daniel]

You could probably use a LaunchedEffect with someParentId as the key to trigger data reload in the ChildVIewModels, when someParentId changes..
LaunchedEffect(key = someParentId) {
childViewModel.reload()
}
This also means that you need to expose someParentId as an observable type (flow, rx) and the observe it as compose state. Optimally pass it as a function paramter all the way down to the child composables.

[Daniel]

I'm not sure a viewmodel holding a reference to several other viewmodels is a good idea. If a ViewModel with a wider scope holds reference to viewmodels with a small scope, then you might have a memory leak when the smaller scoped viewmodels are disposed