how to set the view to last item in recyclerview

Question

I am displaying a list of messages in my chat room and I'm using RecycleView to display. I want the view to be set to the recent message(last message, last item in the list) instead of the first item. I used smoothScrollToPosition but I don't want the list to be scrolled from first to last to view the recent message. I want it to be like whatsapp which when clicked on a chat would show the view of the last message. How can I achieve this?

package com.webapp.chat.activity;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.os.Bundle;
import android.support.v4.content.LocalBroadcastManager;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.DefaultItemAnimator;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.Toolbar;
import android.text.TextUtils;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

import com.android.volley.DefaultRetryPolicy;
import com.android.volley.NetworkResponse;
import com.android.volley.Request;
import com.android.volley.Response;
import com.android.volley.RetryPolicy;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.StringRequest;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import java.sql.Timestamp;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Date;
import java.util.HashMap;
import java.util.Map;

import com.webapp.chat.R;
import com.webapp.chat.adapter.ChatRoomThreadAdapter;
import com.webapp.chat.app.Config;
import com.webapp.chat.app.EndPoints;
import com.webapp.chat.app.MyApplication;
import com.webapp.chat.gcm.NotificationUtils;
import com.webapp.chat.model.Message;
import com.webapp.chat.model.User;

public class ChatRoomActivity extends AppCompatActivity {

    private String TAG = ChatRoomActivity.class.getSimpleName();

    private String userChatRoomId;
    private RecyclerView recyclerView;
    private ChatRoomThreadAdapter mAdapter;
    private ArrayList<Message> messageArrayList;
    private BroadcastReceiver mRegistrationBroadcastReceiver;
    private EditText inputMessage;
    private Button btnSend;
    private String selfUserId;
    private String selfUserName;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_chat_room);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        inputMessage = (EditText) findViewById(R.id.message);
        btnSend = (Button) findViewById(R.id.btn_send);

        Intent intent = getIntent();
        userChatRoomId = intent.getStringExtra("user_id");
        String title = intent.getStringExtra("name");

        getSupportActionBar().setTitle(title);
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);

        if (userChatRoomId == null) {
            Toast.makeText(getApplicationContext(), "User Chat room not found!", Toast.LENGTH_SHORT).show();
            finish();
        }

        recyclerView = (RecyclerView) findViewById(R.id.recycler_view);

        messageArrayList = new ArrayList<>();

        // self user id is to identify the message owner
        selfUserId = MyApplication.getInstance().getPrefManager().getUser().getId();
        selfUserName = MyApplication.getInstance().getPrefManager().getUser().getName();

        mAdapter = new ChatRoomThreadAdapter(this, messageArrayList, selfUserId);

        LinearLayoutManager layoutManager = new LinearLayoutManager(this);
        recyclerView.setLayoutManager(layoutManager);
        recyclerView.setItemAnimator(new DefaultItemAnimator());
        recyclerView.setAdapter(mAdapter);

        mRegistrationBroadcastReceiver = new BroadcastReceiver() {
            @Override
            public void onReceive(Context context, Intent intent) {
                if (intent.getAction().equals(Config.PUSH_NOTIFICATION)) {
                    // new push message is received
                    handlePushNotification(intent);
                }
            }
        };

        btnSend.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                sendMessage();
            }
        });

        fetchChatThread();
    }

    @Override
    protected void onResume() {
        super.onResume();

        // registering the receiver for new notification
        LocalBroadcastManager.getInstance(this).registerReceiver(mRegistrationBroadcastReceiver,
                new IntentFilter(Config.PUSH_NOTIFICATION));

        NotificationUtils.clearNotifications();
    }

    @Override
    protected void onPause() {
        LocalBroadcastManager.getInstance(this).unregisterReceiver(mRegistrationBroadcastReceiver);
        super.onPause();
    }

    /**
     * Handling new push message, will add the message to
     * recycler view and scroll it to bottom
     * */
    private void handlePushNotification(Intent intent) {
        Message message = (Message) intent.getSerializableExtra("message");
        String userChatRoomId = intent.getStringExtra("user_id");

        if (message != null && userChatRoomId != null) {
            messageArrayList.add(message);
            mAdapter.notifyDataSetChanged();
            if (mAdapter.getItemCount() > 1) {
                recyclerView.getLayoutManager().smoothScrollToPosition(recyclerView, null, mAdapter.getItemCount() - 1);
            }
        }
    }

    /**
     * Posting a new message in chat room
     * will make an http call to our server. Our server again sends the message
     * to all the devices as push notification
     * */
    private void sendMessage() {
        final String message = this.inputMessage.getText().toString().trim();

        if (TextUtils.isEmpty(message)) {
            Toast.makeText(getApplicationContext(), "Enter a message", Toast.LENGTH_SHORT).show();
            return;
        }


        /** Create chatroom with the other user after sending the message**/
        String endPointInsert = EndPoints.CHAT_ROOM.replace("_ID_", selfUserId) + "/" + userChatRoomId;
        Log.e(TAG, "endpointInsert: " + endPointInsert);

        StringRequest strReque = new StringRequest(Request.Method.GET,
                endPointInsert, new Response.Listener<String>() {

            @Override
            public void onResponse(String response) {
                Log.e(TAG, "response: " + response);
            }
            }, new Response.ErrorListener() {

            @Override
            public void onErrorResponse(VolleyError error) {
                NetworkResponse networkResponse = error.networkResponse;
                Log.e(TAG, "Volley error: " + error.getMessage() + ", code: " + networkResponse);
                Toast.makeText(getApplicationContext(), "Volley error: " + error.getMessage(), Toast.LENGTH_SHORT).show();
            }
        });

        Date date = new Date();
        String createdAt = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(date);
        Log.e(TAG, "TIMESTAMP:" + createdAt);

        User user = new User(selfUserId, selfUserName);

        final Message msg = new Message();
        msg.setId("");
        msg.setMessage(message);
        msg.setCreatedAt(createdAt);
        msg.setUser(user);

        messageArrayList.add(msg);

        mAdapter.notifyDataSetChanged();
        if (mAdapter.getItemCount() > 1) {
            // scrolling to bottom of the recycler view
            recyclerView.getLayoutManager().smoothScrollToPosition(recyclerView, null, mAdapter.getItemCount() - 1);
        }

        //Log.e(TAG,msg.getId());

        String endPoint = EndPoints.USER_MESSAGE.replace("_ID_", userChatRoomId);

        Log.e(TAG, "endpoint: " + endPoint);

        this.inputMessage.setText("");

        StringRequest strReq = new StringRequest(Request.Method.POST,
                endPoint, new Response.Listener<String>() {

            @Override
            public void onResponse(String response) {
                Log.e(TAG, "response: " + response);

                try {
                    JSONObject obj = new JSONObject(response);

                    // check for error
                    if (obj.getBoolean("error") == false) {
                        JSONObject commentObj = obj.getJSONObject("message");

                        String commentId = commentObj.getString("message_id");
                        String commentText = commentObj.getString("message");
                        String createdAt = commentObj.getString("created_at");

                        JSONObject userObj = obj.getJSONObject("user");
                        String userId = commentObj.getString("from_user_id");
                        String userName = userObj.getString("name");
                        User user = new User(userId, userName);

                        Log.e(TAG, commentId);

                        msg.setId(commentId);

                        /*Message message = new Message();
                        message.setId(commentId);
                        message.setMessage(commentText);
                        message.setCreatedAt(createdAt);
                        message.setUser(user);*/

                        /*messageArrayList.add(msg);

                        mAdapter.notifyDataSetChanged();
                        if (mAdapter.getItemCount() > 1) {
                            // scrolling to bottom of the recycler view
                            recyclerView.getLayoutManager().smoothScrollToPosition(recyclerView, null, mAdapter.getItemCount() - 1);
                        }*/

                    } else {
                        Toast.makeText(getApplicationContext(), "" + obj.getString("message"), Toast.LENGTH_LONG).show();
                    }

                } catch (JSONException e) {
                    Log.e(TAG, "json parsing error: " + e.getMessage());
                    Toast.makeText(getApplicationContext(), "json parse error: " + e.getMessage(), Toast.LENGTH_SHORT).show();
                }
            }
        }, new Response.ErrorListener() {

            @Override
            public void onErrorResponse(VolleyError error) {
                NetworkResponse networkResponse = error.networkResponse;
                Log.e(TAG, "Volley error: " + error.getMessage() + ", code: " + networkResponse);
                Toast.makeText(getApplicationContext(), "Volley error: " + error.getMessage(), Toast.LENGTH_SHORT).show();
                inputMessage.setText(message);
            }
        }) {

            @Override
            protected Map<String, String> getParams() {
                Map<String, String> params = new HashMap<String, String>();
                params.put("user_id", MyApplication.getInstance().getPrefManager().getUser().getId());
                params.put("message", message);

                Log.e(TAG, "Params: " + params.toString());

                return params;
            };
        };


        // disabling retry policy so that it won't make
        // multiple http calls
        int socketTimeout = 0;
        RetryPolicy policy = new DefaultRetryPolicy(socketTimeout,
                DefaultRetryPolicy.DEFAULT_MAX_RETRIES,
                DefaultRetryPolicy.DEFAULT_BACKOFF_MULT);

        strReq.setRetryPolicy(policy);

        //Adding request to request queue
        MyApplication.getInstance().addToRequestQueue(strReque);
        MyApplication.getInstance().addToRequestQueue(strReq);
        Log.i(TAG,msg.getId());
    }


    /**
     * Fetching all the messages of a single chat room
     * */
    private void fetchChatThread() {

        String endPointi = EndPoints.CHAT_USER_THREAD.replace("_ID_", userChatRoomId);
        String endPoint = endPointi + "/" + selfUserId;
        Log.e(TAG, "endPoint: " + endPoint);

        StringRequest strReq = new StringRequest(Request.Method.GET,
                endPoint, new Response.Listener<String>() {

            @Override
            public void onResponse(String response) {
                Log.e(TAG, "response: " + response);

                try {
                    JSONObject obj = new JSONObject(response);

                    // check for error
                    if (obj.getBoolean("error") == false) {
                        JSONArray commentsObj = obj.getJSONArray("messages");

                        for (int i = 0; i < commentsObj.length(); i++) {
                            JSONObject commentObj = (JSONObject) commentsObj.get(i);

                            String commentId = commentObj.getString("message_id");
                            String commentText = commentObj.getString("message");
                            String createdAt = commentObj.getString("created_at");

                            JSONObject userObj = commentObj.getJSONObject("user");
                            String userId = userObj.getString("user_id");
                            String userName = userObj.getString("username");
                            User user = new User(userId, userName);

                            Message message = new Message();
                            message.setId(commentId);
                            message.setMessage(commentText);
                            message.setCreatedAt(createdAt);
                            message.setUser(user);

                            messageArrayList.add(message);
                        }

                        mAdapter.notifyDataSetChanged();
                        if (mAdapter.getItemCount() > 1) {
                            recyclerView.getLayoutManager().smoothScrollToPosition(recyclerView, null, 1);
                        }




                    } else {
                        Toast.makeText(getApplicationContext(), "" + obj.getJSONObject("error").getString("message"), Toast.LENGTH_LONG).show();
                    }

                } catch (JSONException e) {
                    Log.e(TAG, "json parsing error: " + e.getMessage());
                    Toast.makeText(getApplicationContext(), "json parse error: " + e.getMessage(), Toast.LENGTH_SHORT).show();
                }
            }
        }, new Response.ErrorListener() {

            @Override
            public void onErrorResponse(VolleyError error) {
                NetworkResponse networkResponse = error.networkResponse;
                Log.e(TAG, "Volley error: " + error.getMessage() + ", code: " + networkResponse);
                Toast.makeText(getApplicationContext(), "Volley error: " + error.getMessage(), Toast.LENGTH_SHORT).show();
            }
        });

        //Adding request to request queue
        MyApplication.getInstance().addToRequestQueue(strReq);
    }

}

package com.webapp.chat.adapter;

/**
 * Created by COMP on 17-06-2016.
 */
import android.content.Context;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Calendar;
import java.util.Date;

import com.webapp.chat.R;
import com.webapp.chat.model.Message;

public class ChatRoomThreadAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {

    private static String TAG = ChatRoomThreadAdapter.class.getSimpleName();

    private String userId;
    private int SELF = 100;
    private static String today;

    private Context mContext;
    private ArrayList<Message> messageArrayList;

    public class ViewHolder extends RecyclerView.ViewHolder {
        TextView message, timestamp;

        public ViewHolder(View view) {
            super(view);
            message = (TextView) itemView.findViewById(R.id.message);
            timestamp = (TextView) itemView.findViewById(R.id.timestamp);
        }
    }


    public ChatRoomThreadAdapter(Context mContext, ArrayList<Message> messageArrayList, String userId) {
        this.mContext = mContext;
        this.messageArrayList = messageArrayList;
        this.userId = userId;

        Calendar calendar = Calendar.getInstance();
        today = String.valueOf(calendar.get(Calendar.DAY_OF_MONTH));
    }

    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View itemView;

        // view type is to identify where to render the chat message
        // left or right
        if (viewType == SELF) {
            // self message
            itemView = LayoutInflater.from(parent.getContext())
                    .inflate(R.layout.chat_item_self, parent, false);
        } else {
            // others message
            itemView = LayoutInflater.from(parent.getContext())
                    .inflate(R.layout.chat_item_other, parent, false);
        }


        return new ViewHolder(itemView);
    }


    @Override
    public int getItemViewType(int position) {
        Message message = messageArrayList.get(position);
        if (message.getUser().getId().equals(userId)) {
            return SELF;
        }

        return position;
    }

    @Override
    public void onBindViewHolder(final RecyclerView.ViewHolder holder, int position) {
        Message message = messageArrayList.get(position);
        ((ViewHolder) holder).message.setText(message.getMessage());

        String timestamp = getTimeStamp(message.getCreatedAt());

        if (message.getUser().getName() != null)
            timestamp = message.getUser().getName() + ", " + timestamp;

        ((ViewHolder) holder).timestamp.setText(timestamp);
    }

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

    public static String getTimeStamp(String dateStr) {
        SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        String timestamp = "";

        today = today.length() < 2 ? "0" + today : today;

        try {
            Date date = format.parse(dateStr);
            SimpleDateFormat todayFormat = new SimpleDateFormat("dd");
            String dateToday = todayFormat.format(date);
            format = dateToday.equals(today) ? new SimpleDateFormat("hh:mm a") : new SimpleDateFormat("dd LLL, hh:mm a");
            String date1 = format.format(date);
            timestamp = date1.toString();
        } catch (ParseException e) {
            e.printStackTrace();
        }
        return timestamp;
    }
}

Answer 1

Set setReverseLayout=true so that LayoutManager will layout items from end.

Something like this:

LinearLayoutManager layoutManager = new LinearLayoutManager(this);
layoutManager.setReverseLayout(true);
recyclerView.setLayoutManager(layoutManager);

EDIT: This will reverse the data order but not scroll the RecyclerView to the last item. For keeping data order same and simply scrolling the RecyclerView to the last item set setStackFromEnd=true

Sample:

LinearLayoutManager layoutManager = new LinearLayoutManager(this);
layoutManager.setStackFromEnd(true);
recyclerView.setLayoutManager(layoutManager);

Answer 2

Use RecyclerView LayoutManager to scroll item at position

recyclerView.getLayoutManager().scrollToPosition(messageList.size()-1);

And u are good to go