活动重启后Recyclerview不更新

Question

所以，我不确定这个问题的标题，但它就在这里。 我的聊天室有一个 recyclerview。 活动第一次启动时，显示消息没有问题，但是在按下后退按钮回到显示所有聊天室的主要活动后，再次单击同一个聊天室，它什么也不显示。 然后，发送一条消息后，它可以再次显示所有消息。 我不确定发生了什么，请帮助。 哦，我已经尝试了一些东西并浏览了互联网，但是因为我不确定关键字是什么，所以我现在很卡住

好的，事情就是这样

第一个主要活动，（忽略其他 2 个选项卡，它是空的）

主要活动

然后开个聊天室

第一次打开聊天室没问题

然后按返回键，回到MainActivity，然后打开同一个房间，没有聊天显示

聊天室不显示任何内容

然后它在发送新消息后再次显示消息

新消息

我试图将 notifyDataSetChanged() 放在 onStart、onCreate 等各种事件上，但没有任何效果；

这是我的聊天活动

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());
    }
}

然后，这是我的 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);
        }
    }




}

谢谢

Answer 1

那是因为您正在清除子事件侦听器上的列表，而不是在列表中添加新的孩子，也没有将列表传递给适配器。

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

现在通过添加行来更改代码

 @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

就我而言，我使用了onResume()

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

Answer 3

你能把 rv.setAdapter(adapter) 放在 rv.setLayoutManager(manager); 之后吗？ 并且您验证是否始终调用 onDataChange(...) 方法？

Answer 4

您可以在要刷新 recyclerview 的适配器中使用以下代码，例如在@Override public void onBackPressed(){} function 中。 如果你的 chats 数组改变了，你应该刷新这个适配器。

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