Android Jetpack Compose 从 Composable 内的 Fragment 获取活动视图模型

Question

I'm having an issue getting the activity view model from a fragment in a composable

private val birthdayViewModel: BirthdayViewModel by activityViewModels()

When I use viewModels() there is no issue

private val birthdayViewModel: BirthdayViewModel by viewModels()

Fetching the view model in composable like

val birthdayViewModel: BirthdayViewModel = viewModel()
val formItem by birthdayViewModel.birthdayFormItem.observeAsState()

The issue is that the form item errors to null when using activityViewModels but not when using viewModels

When I run in debug mode to check the value of the formItem I get this error message: "Cannot find local variable 'formItem' with type com.form.FormSpec$FormItem"

Could this be a gradle versioning issue?

Please help :)

Answer 1

If you're not using Hilt, assuming that you have instantiated your view model like this in your activity:

val viewModel: YourViewModel by viewModels()

you can get the same instance using this:

val viewModel = viewModel(
    modelClass = YourViewModel::class.java,
    viewModelStoreOwner = LocalContext.current as YourActivity
)

Answer 2

private val activityViewModel: ActivityViewModel by activityViewModels()
private val fragmentViewModel: FragmentViewModel by viewModels()

Composable(fragmentViewModel, activityViewModel)

The problem had to do with scopes. I was not passing the view models into my composable directly, but rather, was doing this in the composable constructor which didn't lead to both of my viewModels having a fragment scope.

Composable(
   fragmentViewModel: FragmentViewModel = viewModel(), 
   activityViewModel: ActivityViewModel = viewModel()
)