如何在更改片段上保存片段回收视图数据？

Question

I have been trying to use onStateInstance but always return null and i dont know how to use ViewModel.

Im getting data from db to recyclerview and i dont want to download again data when navigate to another fragment. (I will update data with swipeRefreshLayout).

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    View v =inflater.inflate(R.layout.fragment_search, container, false);

    
           initComponents(v);
           initRecyclerViewDB(v);


    return v;
}

I need to save my list and dont call method initRecyclerView if my list is not null.

public void initRecyclerViewDB(View v){
    db.collection("post").orderBy("postBy", Query.Direction.ASCENDING).whereNotEqualTo("postBy",mAuth.getCurrentUser().getUid())
            .get().addOnSuccessListener(new OnSuccessListener<QuerySnapshot>() {
        @Override
        public void onSuccess(QuerySnapshot queryDocumentSnapshots) {
            postList.clear();
            for (DocumentSnapshot ds:queryDocumentSnapshots.getDocuments()) {
                postList.add(ds.toObject(Post.class));
            }
            postAdapter.notifyDataSetChanged();
        }
    });

In resume i want to save an arraylist to put in my recyclerview.

Answer 1

The answer was using a view model:

public class YourViewModel extends ViewModel {
private final MutableLiveData<ArrayList<Post>> selectedItem = new MutableLiveData<>();

public void setData(ArrayList<YourList> item){
    selectedItem.setValue(item);
}

public LiveData<ArrayList<YourList>> getSelectedItem(){

    return selectedItem;
 }                                                                          
}

OnCreateView:

 @Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    View v =inflater.inflate(R.layout.fragment_search, container, false);

    viewModel = new ViewModelProvider(requireActivity()).get(PostViewModel.class);
    viewModel.getSelectedItem().observe(getViewLifecycleOwner(), new Observer<ArrayList<Post>>() {
        @Override
        public void onChanged(ArrayList<Post> posts) {
            postList.clear();
            postList.addAll(posts);
            postAdapter.notifyDataSetChanged();
        }
    });


    if (postList.isEmpty()){
        initRecyclerViewDB(v);
    }else {
        Toast.makeText(getContext(), "Save", Toast.LENGTH_SHORT).show();
    }

    initComponents(v);



    return v;
}

If list is empty will import data from db, if not will use viewModel.