Accessing ViewModel in ParentFragment from ChildFragment using viewModels

Issue

I am trying to access the ParentViewModel for ParentFragment from ChildFragment using viewModels. This is my code.

// In ParentFragment

class ParentFragment : Fragment() {
    val parentViewModel: ParentViewModel by viewModels {
        ParentViewModelFactory(getRepository())
    }
    ...
}

// In ChildFragment

class ChildFragment : Fragment() {
    val parentViewModel: ParentViewModel by viewModels(
        { requireParentFragment() }
    )
    ...
}

However, this code only works when I setup a LiveData variable in ParentViewModel and have ParentFragment observe it like so:

parentViewModel.text.observe(this) {
    toast(it)
}

I have no use for observing the ViewModel from inside ParentFragment. I only need it to define the lifecycle for the ChildFragments.

If I get rid of the observation above I get this error:

'java.lang.RuntimeException: Cannot create an instance of class ParentViewModel'

How can I have the ChildFragments access the ParentViewModel without setting up dummy live data objects so as the ParentFragment can observe them.

Solution

In ChildFragment you should pass factory when init it. Try this

class ChildFragment : Fragment() {
    val parentViewModel: ParentViewModel by viewModels(
        { requireParentFragment() }
    ) { ParentViewModelFactory(getRepository()) }
    ...
}

Answered By - Công Hải