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
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【中文标题】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【英文标题】：I am trying to get the correct reference to my Firebase Database child and set the values in my RecyclerView but I am having some issues 【发布时间】：2021-10-16 10:16:07 【问题描述】：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_
android:layout_
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_
android:layout_ />
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/chat_recycler_view"
android:layout_
android:layout_
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_
android:layout_
android:layout_alignParentBottom="true"
android:orientation="horizontal"
android:background="@color/colorBackground">
<EditText
android:id="@+id/chat_msg_edit"
android:layout_
android:layout_
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_
android:layout_
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_
android:layout_
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_
android:layout_
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_
android:layout_
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_
android:layout_
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：
【问题讨论】：
分享崩溃日志你遇到了什么异常 你的数据库规则设置好了吗？ 请将您的数据库截图添加到问题中 如果应用程序崩溃，会有一个堆栈跟踪。请在 logcat 上查找，并将其添加到您的问题中。请将您的数据库结构添加为 JSON 文件或至少作为屏幕截图。也请回复@AlexMamo 嗨@AlexMamo，我已按要求编辑了我的问题。 【参考方案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。
【讨论】：
我根据您的回答更改了代码，现在出现错误：2019-09-11 21:40:01.000 23200-23200/com.lyricsnigeria.lyricsnigeria E/RecyclerView：未连接适配器；跳过布局 2019-09-11 21:40:01.220 23200-23200/com.lyricsnigeria.lyricsnigeria E/AndroidRuntime：致命异常：主进程：com.lyricsnigeria.lyricsnigeria，PID：23200 com.google.firebase.database.DatabaseException：无法将 java.lang.String 类型的对象转换为 com.lyricsnigeria.lyricsnigeria.MessageAdapter 类型 这只是一个警告，通常是因为 this 而发生的。以上是关于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的主要内容，如果未能解决你的问题，请参考以下文章
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