Android nested ViewModel with navigation controller

Question

I have an activity with a fragment inside ( ParentFragment ).

The ParentFragment has a fragment with its navigation controller with multiple fragments.

The ParentFragment's ViewModel has title, subtitle and color properties.

Every time I navigate to another fragment the ParentFragment's ViewModel data should be updated (the fragments are the ones with the data), how can I achieve that?

I know how to share a viewModel, It doesn't fit the project needs, each fragment should have its viewModel, and the same for the ParentFragment .

class ParentFragment: Fragment() {
    private lateinit var parentViewModel: ParentViewModel
}

class ChildFragment: Fragment() {
    private lateinit var childViewModel: ChildViewModel
}

class ParentViewModel : ViewModel() {
     var title: String? = null
     var subtitle: String? = null
     var color: Int? = null
}

class ChildViewModel : ViewModel() {
    init {
        // I need to access ParentViewModel and update title, subtitle and color here.
    }
}

Answer 1

you need to implement ParentViewModel in ChildViewModel

class ChildViewModel : ParentViewModel() {
    init {
        title = "Title"
        subtitle = "Sub Title"
        color = -123454
        // I need to access ParentViewModel and update title, subtitle and color here.
    }
}