More of a better practice question, I have a fragment with a viewpager inside which items are also fragments. Depending on the even in a child fragment inside a viewpager I need to notify the parent fragment (the one that contains viewpager). I see a couple of ways like passing a function to the fragment constructor , using an interface and casting the context to it inside the child fragment. What other (possibly better ways) do you all see for this use case?

Use a

ViewModel

in an activity scope.

It is a single activity pattern , so my viewmodel with activity scope will be responsible for the logic in one of 15 fragments that are present in the app, do you think it is ok?

Let's say

ViewPagerViewModel

that holds only what matters for those pager fragments. They can be notified through

Activity

.

Ok, how would they be notified through activity, having an interface that activity implements and casting it to the context in each fragment?

By observing

LiveData

https://developer.android.com/topic/libraries/architecture/livedata#create_livedata_objects

So they will get instances of that view model that has one instance of livedata, that view model will be a Singleton and they will write events to it ?

You access the same

ViewModel

(activity scoped) in each pager fragment and in their parent activity. Any change / action on pager fragment can trigger

LiveData

in viewmodel.

To access the same view model you have to get the same instance of the same viewmodel in each fragment aka singleton

You do not have to refresh manually if you observe same

LiveData

.