android - 如何将 View 设置为 recyclerview 中的最后一项

Question

我正在我的聊天室中显示消息列表，我正在使用 RecycleView 来显示。我希望将 view 设置为最近的消息(最后一条消息，列表中的最后一项)而不是第一项。我使用了 smoothScrollToPosition 但我不希望列表从头到尾滚动以查看最近的消息。我希望它像 whatsapp 一样，当点击聊天时会显示最后一条消息的 View 。我怎样才能做到这一点？

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

设置 setReverseLayout=true 以便 LayoutManager 将从末尾布局项目。

像这样:

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

编辑:这将反转数据顺序但不会将 RecyclerView 滚动到最后一项。为了保持数据顺序不变，只需将 RecyclerView 滚动到最后一个项目集 setStackFromEnd=true

示例:

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