Chat Android - Firebase，同步延迟问题

Question

几个月来，我使用 Firebase 作为数据库为 Android 系统创建了一个聊天。 我在这里遵循了本指南 (link) 一开始一切都很好，聊天很好，没有任何延迟。然后我开始添加其他细节，例如消息的显示与否以及参与者的状态（在线和离线），从那一刻起，三个问题开始特别显现：

1) 当我将聊天活动更改为转到另一个然后返回聊天时，布局显示为空且没有消息，如果您尝试更改活动，应用程序将自行关闭。我发现我收到了这个错误：

E/RecyclerView：没有附加适配器；跳过布局

这些是构成聊天相关部分的文件：

MessageChat.java

public class MessageChat {

private String sender;
private String receiver;
private String msg;
private String currenttime;
private boolean isseen;

public MessageChat(String sender, String receiver, String msg, String currenttime, boolean isseen){
    this.sender = sender;
    this.receiver = receiver;
    this.msg = msg;
    this.currenttime = currenttime;
    this.isseen = isseen;
}

public MessageChat(){}

public String getSender() {
    return sender;
}

public void setSender(String sender) {
    this.sender = sender;
}

public String getReceiver() {return receiver;}

public void setReceiver(String receiver) { this.receiver = receiver;}

public String getMsg() {
    return msg;
}

public void setMsg(String msg) {
    this.msg = msg;
}

public String getCurrenttime() {
    return currenttime;
}

public void setCurrenttime(String currenttime) {
    this.currenttime = currenttime;
}

public boolean isIsseen() {return isseen;}

public void setIsseen(boolean isseen) {this.isseen = isseen;}
}

msgAdapter.java

public class msgAdapter extends RecyclerView.Adapter<msgAdapter.MsgViewHolder> {

public static final int INT_TYPE_LEFT = 0;
public static final int INT_TYPE_RIGHT = 1;

private static List<MessageChat> mChat;
private static Context context;

private FirebaseUser fuser;

public msgAdapter(List<MessageChat> msg, Context context) {
    this.mChat = msg;
    this.context = context;
}

@Override
public msgAdapter.MsgViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    if (viewType == INT_TYPE_RIGHT) {
        View view = LayoutInflater.from(context).inflate(R.layout.right_message, null);
        msgAdapter.MsgViewHolder msgViewHolder = new msgAdapter.MsgViewHolder(view);
        return msgViewHolder;
    }else{
        View view = LayoutInflater.from(context).inflate(R.layout.left_message, null);
        msgAdapter.MsgViewHolder msgViewHolder = new msgAdapter.MsgViewHolder(view);
        return msgViewHolder;
    }
}

@Override
public void onBindViewHolder(final msgAdapter.MsgViewHolder holder, final int position) {
    MessageChat msg = mChat.get(position);
    holder.show_msg.setText(msg.getMsg());

    if ((position == mChat.size()-1) && msg.getSender().equals(fuser.getUid())){
        if (msg.isIsseen()){
            holder.tv_seen.setText(" Seen ");
            holder.tv_seen.setVisibility(View.VISIBLE);
        }else {
            holder.tv_seen.setText(" Sent ");
            holder.tv_seen.setVisibility(View.VISIBLE);
        }
    }else{
        holder.tv_seen.setVisibility(View.GONE);
    }
}

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

public static class MsgViewHolder extends RecyclerView.ViewHolder {
    TextView username, show_msg, tv_seen;
    public MsgViewHolder(final View itemView) {
        super(itemView);
        show_msg = (TextView) itemView.findViewById(R.id.show_msg);
        tv_seen = (TextView) itemView.findViewById(R.id.tv_seen);
        itemView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // item clicked
                MessageChat msg = mChat.get(getAdapterPosition());
                String ctime = msg.getCurrenttime();
                TastyToast.makeText(context, ctime, TastyToast.LENGTH_LONG, TastyToast.INFO);
            }
        });
    }
}

@Override
public int getItemViewType(int position) {
    fuser = FirebaseAuth.getInstance().getCurrentUser();
    if (mChat.get(position).getSender().equals(fuser.getUid())){
        return INT_TYPE_RIGHT;
    }else{
        return INT_TYPE_LEFT;
    }
}
}

在互联网上，我找到了许多解决此问题的方法，将其替换为：

视图视图 = LayoutInflater.from(context).inflate(R.layout.right_message, null);

到这里：

视图视图 = LayoutInflater.from(context).inflate(R.layout.right_message, parent, false);

但在我的情况下，我只得到了一个漫画和另一个漫画之间的空白聊天。

Homefragment.java

public class HomeFragment extends Fragment {

private HomeViewModel homeViewModel;

private View v;
private ImageButton btn_send;
private EditText et_send_mex;

private DatabaseReference reference;

private msgAdapter mAdapter;
private List<MessageChat> mChat;
private RecyclerView recyclerView;

private FirebaseUser user;
private String Uid, Oid;

private static final String sId = "xyz1";
private static final String pId = "xyz2";


ValueEventListener seenListener;

@Override
public View onCreateView(@NonNull LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {

    homeViewModel =
            ViewModelProviders.of(this).get(HomeViewModel.class);

    // Inflate the layout for this fragment
    v = inflater.inflate(R.layout.fragment_home, container, false);
    btn_send = v.findViewById(R.id.btn_send);
    et_send_mex = v.findViewById(R.id.et_send_mex);

    recyclerView = v.findViewById(R.id.rv_mex);
    recyclerView.setHasFixedSize(true);
    LinearLayoutManager llManager = new LinearLayoutManager(getContext());
    llManager.setStackFromEnd(true);
    recyclerView.setLayoutManager(llManager);

    user = FirebaseAuth.getInstance().getCurrentUser();
    Uid = user.getUid();
    btn_send.setOnClickListener(new View.OnClickListener() {
        public void onClick(View v) {
            // notify = true;
            String m = et_send_mex.getText().toString();
            if (!m.equals("") || !m.equals("\n")){
                if (Uid.equals(pId)){
                    sendMessage(Uid,sId,m);
                }else if (Uid.equals(sId)){
                    sendMessage(Uid,pId,m);
                }
            }
        }
    });
    readMessage();
    return v;
}


private void seenMessage(final String senderId){
    reference = FirebaseDatabase.getInstance().getReference("chats");
    seenListener = reference.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            for (DataSnapshot snapshot: dataSnapshot.getChildren()){
                MessageChat msgchat = snapshot.getValue(MessageChat.class);
                if (msgchat.getReceiver().equals(user.getUid()) && msgchat.getSender().equals(senderId)){
                    HashMap<String, Object> hashMap = new HashMap<>();
                    hashMap.put("isseen", true);
                    snapshot.getRef().updateChildren(hashMap);
                }
            }
        }

        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {

        }
    });
}

private void sendMessage(String sender, String receiver, String message){

    reference = FirebaseDatabase.getInstance().getReference();
    HashMap<String, Object> hashMap = new HashMap<>();
    final Calendar c = Calendar.getInstance();
    int year = c.get(Calendar.YEAR);
    int month = c.get(Calendar.MONTH);
    month = month+1;
    int day = c.get(Calendar.DAY_OF_MONTH);
    int hour = c.get(Calendar.HOUR_OF_DAY);
    int sec = c.get(Calendar.MINUTE);
    String dt = day+" - "+month+" - "+year+", "+hour+":"+sec;
    hashMap.put("currenttime", dt);
    hashMap.put("sender", sender);
    hashMap.put("receiver", receiver);
    hashMap.put("msg", message);
    hashMap.put("isseen", false);
    reference.child("chats").push().setValue(hashMap);
    et_send_mex.setText("");

}

private void readMessage (){

    mChat = new ArrayList<>();
    mAdapter = new msgAdapter(mChat,getContext());
    recyclerView.setAdapter(mAdapter);
    reference = FirebaseDatabase.getInstance().getReference("chats");
    reference.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            mChat.clear();
            for (DataSnapshot snapshot: dataSnapshot.getChildren()){
                MessageChat chat = snapshot.getValue(MessageChat.class);
                mChat.add(chat);
                if (!chat.getSender().equals(Uid)){
                    Oid = chat.getSender();
                    seenMessage(Oid);
                }
            }
            mAdapter.notifyDataSetChanged();
        }

        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {

        }
    });
}

// user status
private void status(String status){
    user = FirebaseAuth.getInstance().getCurrentUser();
    reference = FirebaseDatabase.getInstance().getReference("Users").child(user.getUid());

    HashMap<String, Object> hashMap = new HashMap<>();
    final Calendar c = Calendar.getInstance();
    int year = c.get(Calendar.YEAR);
    int month = c.get(Calendar.MONTH);
    month = month+1;
    int day = c.get(Calendar.DAY_OF_MONTH);
    int hour = c.get(Calendar.HOUR_OF_DAY);
    int sec = c.get(Calendar.MINUTE);
    String dt = day+" - "+month+" - "+year+", "+hour+":"+sec;
    hashMap.put("lastaccess", dt);
    hashMap.put("status", status);
    reference.updateChildren(hashMap);
}

@Override
public void onResume() {
    super.onResume();
    status("online");
    recyclerView.setAdapter(mAdapter);
}

@Override
public void onPause() {
    super.onPause();
    reference.removeEventListener(seenListener);
    status("offline");
}

}

还建议我在这里添加：

@Override
public void onResume() {
  super.onResume();
  status("online");
}

以下代码：

recyclerView.setAdapter(mAdapter);

但是效果很差（也许你可以建议我在这里添加这部分是否正确，非常感谢）

2）当我发送消息时，通常需要很长时间才能到达数据库，假设 Firebase 并不是真正的实时数据库。在这里我没有遇到任何类型的错误，它只是很慢。

3) 后来我也加入了状态的改变，只是当应用程序关闭或在后台时（onPause()），在数据库中将状态设置为离线，否则为在线。但通常它不能正常工作，可能应用程序崩溃或延迟会影响这一点。

我仍然可以为代码的任何其他部分或澄清。 预先感谢您的帮助，并为我的英语不好深表歉意，自去年春天以来我一直在研究此应用程序，但我仍然无法解决这些问题。

Answer 1

您要做的第一件事是删除 onCreate 中的部分。

reference = FirebaseDatabase.getInstance().getReference("chats");
reference.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
        readMessage();
    }

    @Override
    public void onCancelled(@NonNull DatabaseError databaseError) {

    }
});

在这里，您基本上在数据库（聊天）上放置了一个引用，并且每次它发生变化时，它都会调用您的函数 readMessage，该函数将始终覆盖您的消息并将 另一个 侦听器放在同一位置。确保您了解，每次更新 firebase 中的树/路径（聊天）时都会触发 addValueEventListener！

您可以简单地将上面的代码替换为：

readMessage();

这已经确保它正在收听您的数据库。我相信 firebase 并不慢，但两个听众可能会覆盖他们的结果。

关于下一部分我不是100%，但我相信你可以删除

        mAdapter = new msgAdapter(mChat,getContext());
        recyclerView.setAdapter(mAdapter);

来自 onDataChange（在 readMessage 中）并将其直接放在创建 ArrayList 的那部分下。像这样：

mChat = new ArrayList<>();
mAdapter = new msgAdapter(mChat,getContext());
recyclerView.setAdapter(mAdapter);
reference = FirebaseDatabase.getInstance().getReference("chats");

我希望我理解你的问题，我的回答会让你更清楚:)

您好！