CODEWITHSUNDEEP
androidandroid-fragmentsandroid-lifecycleandroid-livedatafragment-lifecycle
ywwynm
ywwynm

Reputation: 11695

How to prevent LiveData observers from being activated when Fragment is not visible

I want to use LiveData in a Fragment to observe the change of some data. Now let's suppose:

  1. Both the Fragment A and Fragment B have their own containers layout in Activity, which means we will call FragmentTransaction#add() separately for them and their onPause() or onResume() will not be called during adding(UI change) because of no FragmentTransaction#replace() action.
  2. B's container is larger than A's, which means if B is added, users cannot see A.
  3. In A there is a LiveData observer named as O, it will observe the change of some data, and update UI according to it. The key is: we want to play some animation for the change, instead of just calling properties setter (like TextView#setText()) naively. For example, maybe the animation is the one played after we called RecyclerView.Adapter#notifyItemInserted()

After adding B, A is considered as invisible to users. However, both the lifecycle of Fragment A or of its View by calling getViewLifecycleOwner() is still on STARTED and RESUMED state. As a result, the animation will play after the data changes observed by O but users cannot see it from the beginning.

How can we solve this problem? Any ideas or answers are appreciated. Thanks in advance.

Upvotes: 5

Views: 2274

Answers (1)

Archie G. Quiñones
Archie G. Quiñones

Reputation: 13668

If you are adding B (which consumes the space supposedly alloted for A), it is better to also remove fragment A. You get multiple benefits for this:

1) You solve your problem. (Thats if youre using viewLifeCycleOwner in observing your LiveData) 2) You decrease memory consumption of your app, since the Fragment A's view will be torn down.

This is

which means we will call FragmentTransaction#add() separately

is also not a problem. Note that you can chain FragmentTransactions such as:

supportFragmentManager.beginTransaction()
    .replace(view1.id, fragmentB)
    .remove(fragmentA)
    .commit()

Upvotes: 2

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