活动重启后Recyclerview不更新

Question

So, I'm not sure about the title of this question but here it goes. I have a recyclerview for my chat room. The first time the activity started it has no problem displaying the messages but after pressing the back button back to the main activity showing all chat rooms then click the same chat room again it displays nothing. Then, after sent a message it can display all the messages again. I'm not sure what happened, help, please. Oh, I already tried a few things and browse the internet but because I'm not sure what the keyword is, so I'm quite stuck now

Okay, here is the thing

First main activity, (ignore the other 2 tabs, it's empty)

Main Activity

Then open a chat room

First time open chat room fine

Then press back button, back to MainActivity, then open the same room and no chat displayed

chat room not displaying anything

Then it displays messages again after sending a new messages

new message

I have tried to place notifyDataSetChanged() on various event like onStart, onCreate etc but nothing works;

here is my chat activity

package com.divistant.chat.ui.chat;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.ViewGroup;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.RelativeLayout;
import android.widget.ScrollView;
import android.widget.TextView;

import com.divistant.chat.R;
import com.divistant.signup.UserModel;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
import com.google.firebase.database.ChildEventListener;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.ValueEventListener;
import com.google.gson.Gson;

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

public class ChatActivity extends AppCompatActivity {
    LinearLayout layout;
    ImageView send;
    EditText message;
    ScrollView scrollView;
    DatabaseReference refrence1;
    DatabaseReference refrence2;
    RecyclerView rv;
    List<ChatModel> chats = new ArrayList<>();
    ChatActivityAdapter adapter;

    FirebaseUser cUser;
    UserModel target;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_chat);
        Log.w("EVENT","ON Create");

        Intent intent = getIntent();
        target = (new Gson()).fromJson(intent.getStringExtra("target"),UserModel.class);

        send = (ImageView)findViewById(R.id.sendButton);
        message = (EditText)findViewById(R.id.messageArea);
        scrollView = (ScrollView)findViewById(R.id.scrollView);
        rv = (RecyclerView) findViewById(R.id.main_chat_rv);
        cUser = FirebaseAuth.getInstance().getCurrentUser();
        adapter = new ChatActivityAdapter(chats);

        final LinearLayoutManager manager = new LinearLayoutManager(ChatActivity.this,
                LinearLayoutManager.VERTICAL, false);
        rv.setLayoutManager(manager);


        refrence1 = FirebaseDatabase.getInstance()
                .getReference()
                .child("messages")
                .child(cUser.getUid() + "_" + target.getUserId());

        refrence2 = FirebaseDatabase.getInstance()
                .getReference()
                .child("messages")
                .child(target.getUserId() + "_" + cUser.getUid());

        send.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                Log.w("SEND","send message");

                if(message.getText().toString().length() > 0){
                    ChatModel chat = new ChatModel();
                    chat.setSender(cUser.getEmail());
                    chat.setMessage(message.getText().toString());
                    chat.setReceiver(target.getEmailAddress());
                    chat.setSenderUid(cUser.getUid());
                    chat.setReceiverUid(target.getUserId());
                    chat.setTimestamp((new Date()).getTime());
                    DatabaseReference ref1 = refrence1.push();
                    ref1.setValue(chat);
                    DatabaseReference ref2 = refrence2.push();
                    ref2.setValue(chat);

                    message.setText("");
                }
            }
        });



        refrence1.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                chats.clear();

                for(DataSnapshot snapshot :dataSnapshot.getChildren()){
                    ChatModel chat = new ChatModel();
                    chat.setSender(snapshot.child("sender").getValue(String.class));
                    chat.setMessage(snapshot.child("message").getValue(String.class));
                    chat.setReceiver(snapshot.child("receiver").getValue(String.class));
                    chat.setSenderUid(snapshot.child("senderUid").getValue(String.class));
                    chat.setReceiverUid(snapshot.child("receiverUid").getValue(String.class));
                    chat.setTimestamp(1592455659978L);

                    chats.add(chat);
                }
                adapter.setmChats(chats);
                adapter.notifyDataSetChanged();
                rv.scrollToPosition(adapter.getItemCount()-1);
                Log.e("[CH]","DATACHANGE " + chats.size());
            }



            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {
                Log.e("[CH]","CANCEL");
            }
        });

        refrence1.addChildEventListener(new ChildEventListener() {
            @Override
            public void onChildAdded(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {
                chats.clear();
                adapter.notifyDataSetChanged();
                rv.scrollToPosition(adapter.getItemCount()-1);
            }

            @Override
            public void onChildChanged(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {
                Log.e("[CH]","DB CHANGE");
            }

            @Override
            public void onChildRemoved(@NonNull DataSnapshot dataSnapshot) {
                Log.e("[CH]","DB REMOVE");
            }

            @Override
            public void onChildMoved(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {
                Log.e("[CH]","Child Moved");
            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {
                Log.e("[CH]","DB ERROR");
            }
        });


        rv.setAdapter(adapter);

    }

    @Override
    protected void onStart() {
        super.onStart();
        Log.e("[CH]","" + adapter.getItemCount());
    }
}

Then, here is my ChatActivityAdapter

package com.divistant.chat.ui.chat;

import android.text.TextUtils;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;

import com.divistant.chat.R;
import com.google.firebase.auth.FirebaseAuth;

import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;

public class ChatActivityAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder>{
    private static final int VIEW_TYPE_ME = 1;
    private static final int VIEW_TYPE_OTHER = 2;
    List<ChatModel> mChats;


    public void setmChats(List<ChatModel> mChats) {
        this.mChats = mChats;
    }

    public ChatActivityAdapter(List<ChatModel> mChats) {
        this.mChats = mChats;
        Log.e("ADAPTER","CONSTRUCTED " + mChats.size());
    }

    @NonNull
    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        LayoutInflater layoutInflater = LayoutInflater.from(parent.getContext());
        RecyclerView.ViewHolder viewHolder = null;
        switch (viewType) {
            case VIEW_TYPE_ME:
                View viewChatMine = layoutInflater.inflate(R.layout.chat_item, parent, false);
                viewHolder = new MyChatViewHolder(viewChatMine);
                break;
            case VIEW_TYPE_OTHER:
                View viewChatOther = layoutInflater.inflate(R.layout.chat_item_other, parent, false);
                viewHolder = new OtherChatViewHolder(viewChatOther);
                break;
        }
        return viewHolder;
    }

    @Override
    public void onBindViewHolder(@NonNull RecyclerView.ViewHolder holder, int position) {
        if (TextUtils.equals(mChats.get(position).senderUid,
                FirebaseAuth.getInstance().getCurrentUser().getUid())) {
            configureMyChatViewHolder((MyChatViewHolder) holder, position);
        } else {
            configureOtherChatViewHolder((OtherChatViewHolder) holder, position);
        }
    }
    private void configureMyChatViewHolder(final MyChatViewHolder myChatViewHolder, int position) {
        ChatModel chat = mChats.get(position);
        SimpleDateFormat sfd = new SimpleDateFormat("hh:mm a");
        String date=sfd.format(new Date(chat.timestamp).getTime());
        myChatViewHolder.senderMsgTime.setText(date);
        myChatViewHolder.txtChatMessage.setText(chat.getMessage());
    }

    private void configureOtherChatViewHolder(final OtherChatViewHolder otherChatViewHolder, int position) {
        final ChatModel chat = mChats.get(position);
        SimpleDateFormat sfd = new SimpleDateFormat("hh:mm a");
        String date=sfd.format(new Date(chat.timestamp).getTime());
        otherChatViewHolder.receiverMsgTime.setText(date);
        otherChatViewHolder.txtChatMessage.setText(chat.getMessage());
    }

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

    @Override
    public int getItemViewType(int position) {
        if (TextUtils.equals(mChats.get(position).senderUid,
                FirebaseAuth.getInstance().getCurrentUser().getUid())) {
            return VIEW_TYPE_ME;
        } else {
            return VIEW_TYPE_OTHER;
        }
    }

    private static class MyChatViewHolder extends RecyclerView.ViewHolder {
        private TextView txtChatMessage, txtUserAlphabet;
        private TextView senderMsgTime;

        public MyChatViewHolder(View itemView) {
            super(itemView);
            txtChatMessage = (TextView) itemView.findViewById(R.id.text_view_chat_message);
            txtUserAlphabet = (TextView) itemView.findViewById(R.id.text_view_user_alphabet);
            senderMsgTime=(TextView) itemView.findViewById(R.id.senderMsgTime);
        }
    }

    private static class OtherChatViewHolder extends RecyclerView.ViewHolder {
        private TextView txtChatMessage, txtUserAlphabet;
        private TextView receiverMsgTime;

        public OtherChatViewHolder(View itemView) {
            super(itemView);
            txtChatMessage = (TextView) itemView.findViewById(R.id.text_view_chat_message_ot);
            txtUserAlphabet = (TextView) itemView.findViewById(R.id.text_view_user_alphabet_ot);
            receiverMsgTime=(TextView) itemView.findViewById(R.id.receiverMsgTime_ot);
        }
    }




}

Thanks

Answer 1

Thats because you are clearing the list on childevent listener and not adding the new child in list and not passing the list to the adapter.

 @Override
        public void onChildAdded(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {
            chats.clear();
            adapter.notifyDataSetChanged();
            rv.scrollToPosition(adapter.getItemCount()-1);
        }

Now change the code by adding the lines

 @Override
        public void onChildAdded(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {
            chats.clear();
            for(DataSnapshot snapshot :dataSnapshot.getChildren()){
                ChatModel chat = new ChatModel();
                chat.setSender(snapshot.child("sender").getValue(String.class));
                chat.setMessage(snapshot.child("message").getValue(String.class));
                chat.setReceiver(snapshot.child("receiver").getValue(String.class));
                chat.setSenderUid(snapshot.child("senderUid").getValue(String.class));
            chat.setReceiverUid(snapshot.child("receiverUid").getValue(String.class));
                chat.setTimestamp(1592455659978L);

                chats.add(chat);
            }
            adapter.setmChats(chats);
            adapter.notifyDataSetChanged();
            rv.scrollToPosition(adapter.getItemCount()-1);
        }

Answer 2

in my case i used onResume()

  @Override
    protected void onResume() {
        super.onResume();
         adapter.notifyDataSetChanged();
    }

Answer 3

Can you put rv.setAdapter(adapter) after rv.setLayoutManager(manager);? And you verify if the method onDataChange(...) its always called??

Answer 4

You can use the following code in the adapter where you want to refresh recyclerview, for example in @Override public void onBackPressed(){} function. If your chats array changed, you should refresh this adapter.

mAdapter = new ChatActivityAdapter(context, chats.get(chats.size() - 1), chats);
recyclerView.setAdapter(mAdapter);