我正在尝试获取对我的 Firebase 数据库子项的正确引用并在我的 RecyclerView 中设置值，但我遇到了一些问题

Question

我正在尝试填充我的 RecyclerView ViewHolder，但我似乎遇到了困难。我认为这可能是因为数据库引用不正确，但我不太确定我做错了什么。

我尝试使用 childEventListener 中的数据快照从我的 firebase db 中检索值并传递给 RecyclerView，但不幸的是没有成功

    private var mAuth: FirebaseAuth? = null
    private var mChatKey: String? = null
    private var mDatabase: DatabaseReference? = null
    private var mMsgRef: DatabaseReference? = null

    private var mRecyclerView: RecyclerView? = null

    private var inputMsg: EditText? = null
    private var sendMsgBtn: ImageView? = null


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

        mChatKey = intent.extras!!.getString("Chat_id")

        mAuth = FirebaseAuth.getInstance()
        mDatabase = FirebaseDatabase.getInstance().reference.child("Chat").child(mChatKey!!).child("messages")


        val toolbar: Toolbar = findViewById(R.id.chat_toolbar) //make toolbar value and get xml toolbar id
        toolbar.title = "Lyrics Nigeria"
        setSupportActionBar(toolbar)
        if (supportActionBar != null) {
            supportActionBar!!.setDisplayHomeAsUpEnabled(true)
            supportActionBar!!.setDisplayShowHomeEnabled(true)
        }//set back button on toolbar


        inputMsg = findViewById(R.id.chat_msg_edit)
        sendMsgBtn = findViewById(R.id.chat_send_btn)


        sendMsgBtn!!.setOnClickListener {
            saveMsgToDatabase()
            inputMsg!!.text = null
        }

        mRecyclerView = findViewById(R.id.chat_recycler_view)
        mRecyclerView!!.layoutManager = LinearLayoutManager(this)
    }

    override fun onStart() {
        super.onStart()
        mDatabase!!.addChildEventListener(object : ChildEventListener {//set lyrics body to firebase database value

            override fun onChildAdded(dataSnapshot: DataSnapshot, p1: String?) {
                if (dataSnapshot.exists()){
                    Toasty.normal(this@ChatActivity, dataSnapshot.child("message").toString()).show()
                    displayMessage()
                }

            }

            override fun onChildChanged(dataSnapshot: DataSnapshot, p1: String?) {
            }

            override fun onChildMoved(dataSnapshot: DataSnapshot, p1: String?) {
            }

            override fun onChildRemoved(dataSnapshot: DataSnapshot) {
            }
            override fun onCancelled(databaseError: DatabaseError) {
            }
        })
    }

    private fun saveMsgToDatabase() {
        val messageKey = mDatabase!!.push().key
        val message = inputMsg!!.text.toString()
        val dateTime = SimpleDateFormat("MMM dd, yyyy HH:mm a", Locale.getDefault()).format(Date())

        val allMessageKey: HashMap<String, Any> = HashMap()
        mDatabase!!.updateChildren(allMessageKey)
        mMsgRef = mDatabase!!.child(messageKey!!)

        val msgInfoMap: HashMap<String, Any> = HashMap()
        msgInfoMap.put("name", mAuth!!.currentUser!!.displayName.toString())
        msgInfoMap.put("message", message)
        msgInfoMap.put("time", dateTime)
        mMsgRef!!.updateChildren(msgInfoMap)


    }

    private fun displayMessage() {
         val mDatabaseMsgs = mDatabase!!.push().key
        val mRef = mDatabase!!.child(mDatabaseMsgs!!)
        val firebaseRecyclerAdapter = object : FirebaseRecyclerAdapter<MessageAdapter, ChatViewHolder>(MessageAdapter::class.java, R.layout.layout_listitem_inmsg_chat, ChatViewHolder::class.java, mRef) {
         override fun populateViewHolder(viewHolder: ChatViewHolder, model: MessageAdapter, position: Int) {

             viewHolder.setName(model.userName!!)
             viewHolder.setMessage(model.userMessage!!)
             viewHolder.setTime(model.msgTime!!)

         }
     }
     mRecyclerView!!.adapter = firebaseRecyclerAdapter
    }


    class ChatViewHolder(val mView: View) : RecyclerView.ViewHolder(mView) {
        fun setName(name: String) {
            val userName = mView.findViewById<View>(R.id.user_display_text) as TextView
            userName.text = name
        }

        fun setMessage(message: String) {
            val userMessage = mView.findViewById<View>(R.id.msg_display_text) as TextView
            userMessage.text = message
        }

        fun setTime(time: String) {
            val msgTime = mView.findViewById<View>(R.id.time_display_text) as TextView
            msgTime.text = time
        }
    }
}

当我输入上面的代码时，应用程序崩溃了，到目前为止，我可以达到 db 值的唯一方法是使用 childEventListener 但无法填充 viewHolder。 将不胜感激任何帮助。谢谢。

以下是错误报告：

2019-09-11 17:08:42.290 6961-6961/? E/RecyclerView: Cannot scroll to position a LayoutManager set. Call setLayoutManager with a non-null argument.
2019-09-11 17:08:42.347 6961-6961/? E/RecyclerView: Cannot scroll to position a LayoutManager set. Call setLayoutManager with a non-null argument.
2019-09-11 17:08:42.453 10677-10677/com.lyricsnigeria.lyricsnigeria E/RecyclerView: No adapter attached; skipping layout
2019-09-11 17:08:43.283 6961-7153/? E/native: personalized-decoder.cc:832 Cannot create punctuation prediction model.
2019-09-11 17:08:43.283 6961-7153/? E/native: personalized-decoder.cc:839 Cannot create graph rescoring model.
2019-09-11 17:08:43.386 6961-6961/? E/RecyclerView: Cannot scroll to position a LayoutManager set. Call setLayoutManager with a non-null argument.
2019-09-11 17:08:43.717 6961-6961/? E/RecyclerView: Cannot scroll to position a LayoutManager set. Call setLayoutManager with a non-null argument.
2019-09-11 17:08:44.204 6961-6961/? E/RecyclerView: Cannot scroll to position a LayoutManager set. Call setLayoutManager with a non-null argument.
2019-09-11 17:08:44.213 6961-6961/? E/RecyclerView: Cannot scroll to position a LayoutManager set. Call setLayoutManager with a non-null argument.
2019-09-11 17:08:44.223 6961-6961/? E/RecyclerView: Cannot scroll to position a LayoutManager set. Call setLayoutManager with a non-null argument.
2019-09-11 17:08:44.284 6961-6961/? E/RecyclerView: Cannot scroll to position a LayoutManager set. Call setLayoutManager with a non-null argument.
2019-09-11 17:08:44.368 6961-6961/? E/RecyclerView: Cannot scroll to position a LayoutManager set. Call setLayoutManager with a non-null argument.
2019-09-11 17:08:44.547 6961-6961/? E/RecyclerView: Cannot scroll to position a LayoutManager set. Call setLayoutManager with a non-null argument.
2019-09-11 17:08:48.806 11188-11188/? E/ACRA: Skipping ANR Detector for process: com.instagram.android:mqtt
2019-09-11 17:08:50.051 6961-6961/? E/RecyclerView: Cannot scroll to position a LayoutManager set. Call setLayoutManager with a non-null argument.
2019-09-11 17:08:50.414 6961-6961/? E/RecyclerView: Cannot scroll to position a LayoutManager set. Call setLayoutManager with a non-null argument.
2019-09-11 17:08:50.635 6961-6961/? E/RecyclerView: Cannot scroll to position a LayoutManager set. Call setLayoutManager with a non-null argument.
2019-09-11 17:08:50.823 6961-6961/? E/RecyclerView: Cannot scroll to position a LayoutManager set. Call setLayoutManager with a non-null argument.
2019-09-11 17:08:51.465 6961-6961/? E/RecyclerView: Cannot scroll to position a LayoutManager set. Call setLayoutManager with a non-null argument.
2019-09-11 17:08:52.501 6961-6961/? E/RecyclerView: Cannot scroll to position a LayoutManager set. Call setLayoutManager with a non-null argument.
2019-09-11 17:08:52.523 6961-6961/? E/RecyclerView: Cannot scroll to position a LayoutManager set. Call setLayoutManager with a non-null argument.
2019-09-11 17:08:52.613 6961-6961/? E/RecyclerView: Cannot scroll to position a LayoutManager set. Call setLayoutManager with a non-null argument.
2019-09-11 17:08:52.656 6961-6961/? E/RecyclerView: Cannot scroll to position a LayoutManager set. Call setLayoutManager with a non-null argument.
2019-09-11 17:08:52.696 6961-6961/? E/RecyclerView: Cannot scroll to position a LayoutManager set. Call setLayoutManager with a non-null argument.
2019-09-11 17:08:52.882 6961-6961/? E/RecyclerView: Cannot scroll to position a LayoutManager set. Call setLayoutManager with a non-null argument.

ChatActivity xml：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/color4"
    android:keepScreenOn="false"
    tools:context=".ChatActivity"
    android:id="@+id/chat_recycler_lyt">


    <include
        android:id="@+id/chat_toolbar"
        layout="@layout/toolbar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

    <androidx.recyclerview.widget.RecyclerView
            android:id="@+id/chat_recycler_view"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:overScrollMode="never"
            android:layout_above="@+id/input_msg_lyt"
            android:layout_below="@+id/chat_toolbar"
        tools:listitem="@layout/layout_listitem_inmsg_chat"/>

    <RelativeLayout
        android:id="@+id/input_msg_lyt"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:orientation="horizontal"
        android:background="@color/colorBackground">

        <EditText
            android:id="@+id/chat_msg_edit"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:background="@drawable/edit_text_bg2"
            android:padding="10dp"
            android:layout_marginTop="8dp"
            android:layout_marginBottom="8dp"
            android:layout_marginLeft="20dp"
            android:layout_marginStart="20dp"
            android:hint="@string/start_typing"
            android:singleLine="false"
            android:inputType="textCapSentences|textMultiLine"
            android:layout_toLeftOf="@+id/chat_send_btn"
            android:layout_toStartOf="@+id/chat_send_btn" />

        <ImageView
            android:id="@+id/chat_send_btn"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            app:srcCompat="@drawable/ic_send_black_24dp"
            android:layout_gravity="center"
            android:layout_margin="8dp"
            android:layout_alignParentRight="true"
            android:layout_alignParentEnd="true" />
    </RelativeLayout>

</RelativeLayout>

list_item xml：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="300dp"
    android:layout_height="wrap_content"
    android:orientation="vertical"
    android:layout_gravity="start|bottom"
    android:layout_margin="5dp"
    android:background="@drawable/chat_bg">
        <TextView
            android:id="@+id/user_display_text"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginStart="5dp"
            android:padding="2dp"
            android:textAllCaps="false"
            android:textColor="@color/colorBlack"
            android:textSize="12sp"
            android:layout_marginLeft="5dp" />

        <TextView
            android:id="@+id/msg_display_text"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginStart="2dp"
            android:layout_marginLeft="2dp"
            android:padding="10dp"
            android:textAllCaps="false"
            android:textColor="@color/colorBlack"
            android:textSize="16sp" />

        <TextView
            android:id="@+id/time_display_text"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginEnd="15dp"
            android:layout_marginRight="15dp"
            android:padding="2dp"
            android:textAllCaps="false"
            android:textColor="@color/colorBlack"
            android:textSize="12sp"
            android:layout_gravity="end|bottom"/>
</LinearLayout>

适配器类：

class MessageAdapter {
    var userName:String? = null
    var userMessage:String? = null
    var msgTime:String? = null

    constructor(userName:String, userMessage:String, msgTime:String) {
        this.userName = userName
        this.userMessage = userMessage
        this.msgTime = msgTime

    }
    constructor() {}
}

还有我的数据库截图：

Answer 1

代码中的问题在于MessageAdapter 类中的字段名称与数据库中属性的名称不同。您在 MessageAdapter 类中有三个字段，分别名为 userName、userMessage 和 msgTime，而在数据库中我看到名称不同，name、message 和 time，这是 不正确。名称必须匹配。

一种解决方案可能是更改 MessageAdapter 类中的字段名称，如下所示：

class MessageAdapter {
    var name:String? = null
    var message:String? = null
    var time:String? = null

    constructor(name:String, message:String, time:String) {
        this.name = name
        this.message = message
        this.time = time

    }
    constructor() {}
}

您的问题将得到解决，或者您可以使用注释

class MessageAdapter {
    @get:PropertyName("name")
    @set:PropertyName("name")
    var userName:String? = null
    @get:PropertyName("message")
    @set:PropertyName("message")
    var userMessage:String? = null
    @get:PropertyName("time")
    @set:PropertyName("time")
    var msgTime:String? = null

    constructor(userName:String, userMessage:String, msgTime:String) {
        this.userName = userName
        this.userMessage = userMessage
        this.msgTime = msgTime

    }
    constructor() {}
}

你得到以下错误：

E/RecyclerView：无法滚动定位 LayoutManager 集。使用非空参数调用 setLayoutManager。

因为您试图滚动到实际上不存在的最后一个位置，因为您的RecyclerView 中没有显示任何项目。