Mercury-IM/app/src/main/java/org/mercury_im/messenger/ui/roster/RosterFragment.java

package org.mercury_im.messenger.ui.roster;

import androidx.lifecycle.Observer;
import androidx.lifecycle.ViewModelProviders;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import android.os.Bundle;
import androidx.recyclerview.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import org.mercury_im.messenger.R;
import org.mercury_im.messenger.persistence.room.model.RoomContactModel;

import java.util.ArrayList;
import java.util.List;

/**
 * A placeholder fragment containing a simple view.
 */
public class RosterFragment extends Fragment {

    private RosterViewModel rosterViewModel;
    private RosterRecyclerViewAdapter recyclerViewAdapter;
    private RecyclerView recyclerView;

    public RosterFragment() {

    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_roster_entry_list, container, false);

        recyclerView = view.findViewById(R.id.roster_entry_list__recycler_view);
        recyclerViewAdapter = new RosterRecyclerViewAdapter(new ArrayList<>());
        recyclerView.setAdapter(recyclerViewAdapter);

        rosterViewModel = ViewModelProviders.of(getActivity()).get(RosterViewModel.class);
        observeViewModel(rosterViewModel);

        return view;
    }

    private void observeViewModel(RosterViewModel viewModel) {
        viewModel.getRosterEntryList().observe(this, new Observer<List<RoomContactModel>>() {
            @Override
            public void onChanged(@Nullable List<RoomContactModel> rosterEntries) {
                if (rosterEntries == null) {
                    return;
                }
                recyclerViewAdapter.setItems(rosterEntries);
            }
        });
    }
}