Невозможно отобразить список сообщений из базы данных Firebase в реальном времени, используя представление переработчика с пользовательским адаптером

Question

Я пытаюсь отобразить сообщения, которые пользователь отправляет в базу данных Firebase в реальном времени, используя представление Recyler в Android, но мой экран чата отображает пустой экран, даже когда база данных Firebase обновляется.

это файл MainChatActivity.kt

class MainChatActivity : AppCompatActivity() {

var mDisplayName:String?=null

var databaseref:DatabaseReference?=null
var msgEditText:EditText?=null
var sendButton:ImageButton?=null
var msgRow:RecyclerView?=null

var Adapter:Adapter?=null
var viewManager: RecyclerView.LayoutManager?=null

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main_chat)

    msgEditText = findViewById(R.id.messageInput)
    sendButton=findViewById(R.id.sendButton)

    msgRow=findViewById<RecyclerView>(R.id.chat_list_view)


    Adapter = Adapter(databaseref,mDisplayName,this@MainChatActivity)
    viewManager = LinearLayoutManager(this@MainChatActivity)
    msgRow?.apply {
        layoutManager=viewManager
        adapter=Adapter
        itemAnimator=DefaultItemAnimator()
    }

}

override fun onResume() {
    super.onResume()

    databaseref=FirebaseDatabase.getInstance().getReference()

    msgEditText?.setOnEditorActionListener(TextView.OnEditorActionListener { v, actionId, event ->
        sendMessage(msgEditText?.text.toString())
        true
    })

    sendButton?.setOnClickListener {
        sendMessage(msgEditText?.text.toString())
    }
}

private fun sendMessage(message: String) {

    if (message != "") {
        val prefs: SharedPreferences = this@MainChatActivity.getSharedPreferences(RegisterActivity.static.myPrefs, 0)
        mDisplayName=prefs.getString("DisaplayName","DisaplayName")
        Log.v("displaynamechat",mDisplayName.toString())
        if(prefs.getString("DisaplayName",null) =="")
        {
            mDisplayName="Anonymous"
        }
        val chat = Messages(message, mDisplayName.toString())
        databaseref?.child("messages")?.push()?.setValue(chat)
        msgEditText?.setText("")
    }

}

public override fun onStart() {
    super.onStart()

}

override fun onStop() {
    super.onStop()
    Adapter?.cleanup()
}
}

это файл Adapter.kt, который я использую для представления переработчика

class Adapter (databaseRef: DatabaseReference?, displayName: String?, context: Context): RecyclerView.Adapter<Adapter.viewHolder>(){

var databaseRef:DatabaseReference?=null
var author:String?=null
var context:Context?=null
lateinit var dataSnap:ArrayList<DataSnapshot>

private val mListener = object : ChildEventListener {
    override fun onChildAdded(dataSnapshot: DataSnapshot, s: String?) {

        dataSnap.add(dataSnapshot)
        notifyDataSetChanged()
    }

    override fun onChildChanged(dataSnapshot: DataSnapshot, s: String?) {

    }

    override fun onChildRemoved(dataSnapshot: DataSnapshot) {

    }

    override fun onChildMoved(dataSnapshot: DataSnapshot, s: String?) {

    }

    override fun onCancelled(databaseError: DatabaseError) {

    }
}

init {
    this.databaseRef=databaseRef?.child("messages")
    this.author=displayName
    this.context=context
    this.dataSnap = java.util.ArrayList<DataSnapshot>()
    this.databaseRef?.addChildEventListener(this.mListener)
}

override fun onCreateViewHolder(p0: ViewGroup, p1: Int): viewHolder {
    var itemvew= LayoutInflater.from(p0.context)
        .inflate(R.layout.chat_msg_row,p0,false)
    return viewHolder(itemvew)

}

override fun getItemCount(): Int {
    return dataSnap.size
}

override fun onBindViewHolder(p0: viewHolder, p1: Int) {
    var gettingcurrentSnap= dataSnap.get(p0.adapterPosition)

    var meessageClass = gettingcurrentSnap.getValue(Messages::class.java)

    Log.v("flashchat message",meessageClass?.msg)

    p0.msgText?.setText(meessageClass?.msg)
    if(author =="")
        author="Anonymous"

    p0.author?.setText(meessageClass?.author)

    if (meessageClass?.author == author) {
        p0.body?.setBackgroundResource(R.drawable.bubble2)
        p0.body?.gravity = Gravity.END
        p0.author?.setTextColor(Color.GREEN)
    }
    else
    {
        p0.body?.setBackgroundResource(R.drawable.bubble1)
        p0.body?.gravity = Gravity.START
        p0.author?.setTextColor(Color.BLUE)
    }
}

class viewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
    var msgText: TextView?=null
    var author: TextView?=null
    var body:LinearLayout?=null

    init {
        msgText=itemView.findViewById(R.id.message)
        author=itemView.findViewById(R.id.author)
        body=itemView.findViewById(R.id.singleMessageContainer)
    }
}

internal fun cleanup() {

    databaseRef?.removeEventListener(mListener)
}

}

это класс для хранения сообщений из datasnapshot из firebase Messages.kt class

class Messages {
var author: String=""
var msg: String=""

private constructor() {}

constructor(author: String, text: String) {
    this.author = author
    this.msg = text
}
}

activity_main_chat.xml

<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"
            android:background="@color/light_purple">

<android.support.v7.widget.RecyclerView
        android:id="@+id/chat_list_view"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_above="@+id/listFooter"
        android:layout_alignParentTop="true"
        android:divider="@null"
        android:dividerHeight="0dp"
        android:transcriptMode="alwaysScroll" />

<LinearLayout
        android:id="@+id/listFooter"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:orientation="horizontal"
        android:gravity="bottom">

    <EditText
            android:id="@+id/messageInput"
            android:layout_width="0dp"
            android:layout_height="fill_parent"
            android:layout_weight="1"
            android:textColor="@color/black"
            android:textColorHint="@color/black"
            android:hint="@string/prompt_msg"
            android:imeActionLabel="@string/action_send"
            android:imeOptions="actionUnspecified"
            android:inputType="textCapSentences|textAutoCorrect"
            android:maxLines="1"
            android:gravity="center_horizontal"/>

    <ImageButton
            android:id="@+id/sendButton"
            android:padding="10dp"
            android:background="@drawable/circle_shape"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:src="@android:drawable/ic_menu_send"
            android:contentDescription="@string/action_send"/>
</LinearLayout>


</RelativeLayout>

chat_msg_row.xml

<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:id="@+id/singleMessageContainer"
    android:orientation="vertical">

<TextView
        android:id="@+id/author"
        android:paddingLeft="10dp"
        android:paddingRight="10dp"
        android:layout_gravity="start"
        android:textColor="@color/green"
        android:gravity="center_vertical"
        android:textSize="15sp"
        android:textStyle="bold"
        android:text="@string/prompt_msg"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

<TextView
        android:id="@+id/message"
        android:layout_gravity="start"

        android:gravity="center_vertical"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="5dip"
        android:padding="10dp"
        android:textSize="15sp"
        android:text="@string/sample_message"
        android:textColor="@android:color/primary_text_light"
/>

</LinearLayout>