ViewModel for Fragment instead accessing Activity ViewModel?

Question

The problem is quite straightforward. The question is in context of using ViewModels, LiveData and other related Lifecycle aware arch approaches.
I have an Activity with Na

Answer 1

What i would suggest you can do is handle two ViewModel for your entire use case.

Make one ViewModel

Let's say MyActivityViewModel to handle all logic related for activity level. So, if any fragment logic is directly related to your activity then share your ViewModel like below :

ViewModelProviders.of(getActivity()).get(MyActivityViewModel.class); // Like this in fragment.

&

ViewModelProviders.of(this).get(MyActivityViewModel.class); // Like this in activity.

This will share common ViewModel between your activity and fragment.

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Another ViewModel would go for FirstFragment in your case if you have to share logic between your ChildFragment :

Here you can share ViewModel let's say FragmentViewModel like below:

ViewModelProviders.of(this).get(FragmentViewModel.class); // Like this in FirstFragment which is having view pager.

&

ViewModelProviders.of(getParentFragment()).get(FragmentViewModel.class); // Like this in View pager fragments, getParentFragment() is First fragment in our case.

Although, we can still use our activity level MyActivityViewModel in our child fragments from FirstFragment like :

ViewModelProviders.of(getActivity()).get(MyActivityViewModel.class);