无法使用FirebaseListAdapter更新ListView

Question

我正在使用this android tutorial修改我的简单Android应用程序以使用聊天功能。但我无法从Firebase实时数据库更新列表视图。我可以写入数据库，但无法读取数据并显示它。我尝试了不同的解决方案，但它根本不起作用。这是我搜索不同解决方案和修改项目后的最新代码。

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.text.format.DateFormat;
import android.view.View;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.TextView;

import com.firebase.ui.database.FirebaseListAdapter;
import com.firebase.ui.database.FirebaseListOptions;
import com.google.firebase.auth.FirebaseAuth;
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.Query;
import com.google.firebase.database.ValueEventListener;

public class ChatActivity extends AppCompatActivity {
    FirebaseDatabase database = FirebaseDatabase.getInstance();
    public DatabaseReference myRef = database.getReference("message");
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_chat);
        displayMessage();
        myRef.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                displayMessage();
            }

            @Override
            public void onCancelled(DatabaseError error) {
            }
        });
    }

    public void sendMessage(View v) {
        EditText input = findViewById(R.id.input);
        myRef.push()
                .setValue(new ChatMessage(input.getText().toString(),
                        getUser())
                );
        input.setText("");
        displayMessage();
    }

    private String getUser() throws NullPointerException {
        return FirebaseAuth.getInstance()
                .getCurrentUser()
                .getDisplayName();
    }

    private void displayMessage() {
        ListView listOfMessages = findViewById(R.id.list_of_messages);
        FirebaseListAdapter<ChatMessage> adapter;
        Query query = myRef;
        FirebaseListOptions<ChatMessage> options = new FirebaseListOptions.Builder<ChatMessage>()
                .setQuery(query, ChatMessage.class)
                .setLayout(R.layout.message)
                .build();
        adapter = new FirebaseListAdapter<ChatMessage>(options) {
            @Override
            protected void populateView(View v, ChatMessage model, int position) {
                TextView messageText = v.findViewById(R.id.message_text);
                TextView messageUser = v.findViewById(R.id.message_user);
                TextView messageTime = v.findViewById(R.id.message_time);
                messageText.setText(model.getMessageText());
                messageUser.setText(model.getMessageUser());
                messageTime.setText(DateFormat.format("dd-MM-yyyy (HH:mm:ss)",
                        model.getMessageTime()));
            }
        };
        listOfMessages.setAdapter(adapter);
    }
}

子消息的JSON文件是

    {
  "message" : {
    "-L2hcJLFvPY0G1pjj-dY" : {
      "messageText" : "Hi How are you? ",
      "messageTime" : 1515815206276,
      "messageUser" : ""
    },
    "-L2hcKsBwdQX-h_tSHpl" : {
      "messageText" : "It is fine. ",
      "messageTime" : 1515815212543,
      "messageUser" : ""
    },
    "-L2hcMthlhbllagf9d8u" : {
      "messageText" : "Some text for texting",
      "messageTime" : 1515815220832,
      "messageUser" : ""
    }
  }
}

以及ChatMessage.java文件代码

import java.util.Date;

public class ChatMessage {
    private String messageText;
    private String messageUser;
    private long messageTime;

    public ChatMessage(String messageText, String messageUser) {
        this.messageText = messageText;
        this.messageUser =messageUser;
        messageTime = new Date().getTime();
    }
    public ChatMessage(){

    }
    public String getMessageText() {
        return messageText;
    }

    public String getMessageUser() {
        return messageUser;
    }

    public long getMessageTime() {
        return messageTime;
    }
}