使用Firebase的简单聊天应用

Question

大家好，我是学生，我很高兴再次和你在一起，我正在学习android开发，现在我在处理服务器和数据库的这一章和我在这个应用程序（简单的聊天应用程序）中面临一种错误，让你在firebase数据库中共享文本java代码

package com.example.hfpro.myapplication;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.EditText;
import android.widget.ListView;

import com.firebase.client.DataSnapshot;
import com.firebase.client.Firebase;
import com.firebase.client.FirebaseError;
import com.firebase.client.ValueEventListener;

import java.util.ArrayList;
import java.util.Map;

public class MainActivity extends AppCompatActivity {

    Firebase database ;
    ArrayList<String> arrayList ;
    ListView listView ;
    EditText editText ;
    ArrayAdapter adapter ;
    Firebase chat ;
    Map<String , Object> mapRetrived ;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Firebase.setAndroidContext(this);
        database = new Firebase(MY FIREBASE URL);
        chat = database.child("chat") ; // THE NAME OF THE CHILD
        listView = (ListView) findViewById(R.id.listView) ;
        arrayList = new ArrayList<>() ;
        editText = (EditText) findViewById(R.id.textToSend) ;
    adapter = new ArrayAdapter<String>(this ,              android.R.layout.simple_list_item_1 , arrayList);

       listView.setAdapter(adapter);
        adapter.notifyDataSetChanged();
    }

    @Override
    protected void onStart() {
        super.onStart();
        chat.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                arrayList.clear();
                 mapRetrived = (Map<String, Object>) dataSnapshot.getValue();
                String[] strs = (String[]) mapRetrived.values().toArray();
                for(String s : strs)
                {
                    arrayList.add(s);
                }
            }

            @Override
            public void onCancelled(FirebaseError firebaseError) {

            }
        });
    }
    public void send(View v)
    {
        String data = editText.getText().toString() ;
        //arrayList.add(data);
        editText.setText("");
        chat.child("chat1").push().setValue(data);
        adapter.notifyDataSetChanged();

    }
}

并且xml文件非常简单

    <?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.hfpro.myapplication.MainActivity">

    <ListView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/listView"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:layout_above="@+id/textToSend" />

    <EditText
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:id="@+id/textToSend"
        android:layout_alignParentBottom="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:layout_toLeftOf="@+id/button"
        android:layout_toStartOf="@+id/button" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/send"
        android:id="@+id/button"
        android:layout_alignParentBottom="true"
        android:layout_alignParentRight="true"
        android:layout_alignParentEnd="true"
        android:onClick="send"/>

</RelativeLayout>

感谢您阅读和感谢您的时间。