Как обновить список Firebase?

public class MainActivity extends AppCompatActivity {

    private RecyclerView recyclerView;
    private List<UserModel> result;
    private UserAdapter adapter;

    CalendarView calendarView;
    String selectedDate;

    private FirebaseDatabase database;
    private DatabaseReference reference;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_email_password);

        Calendar c = Calendar.getInstance();
        SimpleDateFormat sdf = new SimpleDateFormat("dd_MM_yyyy");
        Date date = new Date();
        calendarView = (CalendarView) findViewById(R.id.calendarView);
        selectedDate = sdf.format(date);
        try {
            calendarView.setOnDateChangeListener(new CalendarView.OnDateChangeListener() {
                @Override
                public void onSelectedDayChange(@NonNull CalendarView calendarView, int year, int month, int dayOfMonth) {
                    int mYear = year;
                    int mMonth = month;
                    int mDay = dayOfMonth;
                    selectedDate = new StringBuilder().append(mDay).append("_").append(mMonth + 1).append("_")
                            .append(mYear).toString();
                    Toast.makeText(MainActivity.this, selectedDate, Toast.LENGTH_SHORT).show();
                    reference = database.getReference(selectedDate);
                               }
            });
           database = FirebaseDatabase.getInstance();
            reference = database.getReference(selectedDate);

            result = new ArrayList<>();


            recyclerView = (RecyclerView) findViewById(R.id.userList);
            recyclerView.setHasFixedSize(true);
            LinearLayoutManager llm = new LinearLayoutManager(this);
            llm.setOrientation(LinearLayout.VERTICAL);

            recyclerView.setLayoutManager(llm);


            adapter = new UserAdapter(result);
            recyclerView.setAdapter(adapter);

            updateList();
        } catch (NullPointerException e) {
        }


    }
    private void updateList() {

        reference.addChildEventListener(new ChildEventListener() {
            @Override
            public void onChildAdded(DataSnapshot dataSnapshot, String s) {
                //  result.clear();
                result.add(dataSnapshot.getValue(UserModel.class));
                adapter.notifyDataSetChanged();
            }

            @Override
            public void onChildChanged(DataSnapshot dataSnapshot, String s) {
                UserModel model = dataSnapshot.getValue(UserModel.class);
                int index = getItemIndex(model);

                result.set(index, model);
                adapter.notifyItemChanged(index);

            }

            @Override
            public void onChildRemoved(DataSnapshot dataSnapshot) {

                UserModel model = dataSnapshot.getValue(UserModel.class);
                int index = getItemIndex(model);

                result.remove(index);
                adapter.notifyItemRemoved(index);


            }

            @Override
            public void onChildMoved(DataSnapshot dataSnapshot, String s) {

            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });

    }

    private int getItemIndex(UserModel user) {
        int index = -1;
        for (int i = 0; i < result.size(); i++) {
            if (result.get(i).key.equals(user.key))
                index = i;
            break;
        }
        return index;
    }
}

public class UserAdapter extends RecyclerView.Adapter<UserAdapter.UserViewHolder> {

    private List<UserModel> list;

    public UserAdapter(List<UserModel> list) {
        this.list = list;
    }

    @Override
    public UserViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        return new UserViewHolder(LayoutInflater.from(parent.getContext()).inflate(R.layout.view_item,parent,false));
    }

    @Override
    public void onBindViewHolder(final UserViewHolder holder, int position) {

        UserModel user = list.get(position);
        holder.textName.setText(user.firstName + " "+ user.number);
        holder.textDate.setText(user.date);
        holder.textTime.setText(user.time);
        holder.itemView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Context context = view.getContext();
                Intent intent = new Intent(context,Main2Activity.class);
                context.startActivity(intent);
            }
        });

    }

    @Override
    public int getItemCount() {
        return list.size();
    }

    class UserViewHolder extends RecyclerView.ViewHolder  {
        TextView textName, textTime, textDate;

        public UserViewHolder(View itemView) {
            super(itemView);
            textTime = (TextView) itemView.findViewById(R.id.time);
            textName = (TextView) itemView.findViewById(R.id.text_name);
            textDate = (TextView) itemView.findViewById(R.id.text_date);
        }
    }
}

public class UserModel {
    String firstName,number,key,date,time;
    public UserModel(){
}

    public UserModel(String firstName, String number, String key, String date, String time) {
        this.firstName = firstName;
        this.number = number;
        this.key = key;
        this.date = date;
        this.time = time;
    }

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getNumber() {
        return number;
    }

    public void setNumber(String number) {
        this.number = number;
    }

    public String getKey() {
        return key;
    }

    public void setKey(String key) {
        this.key = key;
    }

    public String getDate() {
        return date;
    }

    public void setDate(String date) {
        this.date = date;
    }

    public String getTime() {
        return time;
    }

    public void setTime(String time) {
        this.time = time;
    }
}