RecyclerView как правильно добавлять данные

import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.graphics.Color;
import android.support.v7.widget.RecyclerView;
import android.text.format.DateFormat;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.LinearLayout;
import android.widget.TextView;
 
import java.util.List;
 
public class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder> {
    private List<Message> mDataset;
 
    public MyAdapter(List<Message> Dataset) {
        this.mDataset = Dataset;
    }
    
    @Override
    public ViewHolder onCreateViewHolder(ViewGroup viewGroup, int i) {
        View v = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.recyclerview_item, viewGroup, false);
        return new ViewHolder(v);
    }
    
    @Override
    public void onBindViewHolder(ViewHolder viewHolder, final int i) {
        final Message record = mDataset.get(i);
        viewHolder.name.setText(String.format("(%d) %s", i+1,record.getMessageText()));
        viewHolder.time.setText(DateFormat.format("dd-MM-yyyy (HH:mm:ss)", record.getMessageTime()));
        if (i % 2 == 0)
            viewHolder.mLinearLayout.setBackgroundColor(Color.WHITE);
        else
            viewHolder.mLinearLayout.setBackgroundColor(Color.rgb(255, 223, 223));
 
        viewHolder.mLinearLayout.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Context context = view.getContext();
                Intent intent = new Intent(context, NoteActivity.class);
                intent.putExtra("ID", i);
                intent.putExtra("OLD_MESSAGE", record.getMessageText());
                ((Activity) context).startActivityForResult(intent, 2);
            }
        });
    }
 
    @Override
    public int getItemCount() {
        return mDataset.size();
    }
    
    class ViewHolder extends RecyclerView.ViewHolder {
        private TextView name;
        private TextView time;
 
        private LinearLayout mLinearLayout;
 
        public ViewHolder(View itemView) {
            super(itemView);
            name = (TextView) itemView.findViewById(R.id.message_textView);
            time = (TextView) itemView.findViewById(R.id.time_textView);
            mLinearLayout = (LinearLayout) itemView.findViewById(R.id.linLayout);
        }
    }
 
}

public ArrayList<Message> message_list = new ArrayList<Message>();

mRecyclerView = (RecyclerView) findViewById(R.id.recycler);
mLayoutManager = new LinearLayoutManager(this);
mRecyclerView.setLayoutManager(mLayoutManager);
mAdapter = new MyAdapter(message_list);
mRecyclerView.setAdapter(mAdapter);

message_list.add(new Message(message));
mRecyclerView.setAdapter(new MyAdapter(message_list));

public class UserAdapter extends RecyclerView.Adapter<UserAdapter.UserViewHolder> {
 
    @Nullable
    private final UserListViewModel mViewModel;
    private final OnUserClickListener mUserClickListener;
 
    List<? extends User> mUserList;
 
    public UserAdapter(@Nullable UserListViewModel viewModel,
                       @NonNull OnUserClickListener userClickListener) {
        mViewModel = viewModel;
        mUserClickListener = userClickListener;
    }
 
    public void setUserList(final List<? extends User> userList) {
        if (mUserList == null) {
            mUserList = userList;
            notifyItemRangeInserted(0, userList.size());
        } else {
            DiffUtil.DiffResult result = DiffUtil.calculateDiff(new DiffUtil.Callback() {
                @Override
                public int getOldListSize() {
                    return mUserList.size();
                }
 
                @Override
                public int getNewListSize() {
                    return userList.size();
                }
 
                @Override
                public boolean areItemsTheSame(int oldItemPosition, int newItemPosition) {
                    return mUserList.get(oldItemPosition).getId()
                            == userList.get(newItemPosition).getId();
                }
 
                @Override
                public boolean areContentsTheSame(int oldItemPosition, int newItemPosition) {
                    User newUser = userList.get(newItemPosition);
                    User oldUser = mUserList.get(oldItemPosition);
                    return newUser.equals(oldUser);
                }
            });
 
            mUserList = userList;
            result.dispatchUpdatesTo(this);
            mViewModel.readyToDisplayUser();
        }
    }
 
    @Override
    public UserViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
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