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com.google.firebase.database.DatabaseException: Can't convert an object of type java.lang.String to type，似乎这个错误总是发生，但我仍然不知道如何解决它。

这是我显示 RecyclerView 的活动：

    package com.example.budget

import android.content.Intent
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.view.Gravity
import android.view.View
import android.widget.ImageButton
import android.widget.TextView
import androidx.drawerlayout.widget.DrawerLayout
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.RecyclerView
import com.example.budget.data.bill
import com.example.budget.login_register.LoginActivity
import com.google.firebase.database.*
import com.google.android.material.navigation.NavigationView
import com.google.firebase.auth.FirebaseAuth
import com.google.firebase.database.DatabaseReference


class TransactionActivity : AppCompatActivity(),NavigationView.OnNavigationItemSelectedListener {
    lateinit var drawer_layout: DrawerLayout
    lateinit var ref: DatabaseReference
    lateinit var database: FirebaseDatabase
    lateinit var nav_view: NavigationView
    lateinit var btnMenu: ImageButton
    var isbtnMenuClicked: Boolean = false
    var id: Int = 0
    var strName =""
    var strEmail = ""
    lateinit var nav_header : View
    lateinit var tvName: TextView
    lateinit var tvEmail: TextView
    lateinit var auth: FirebaseAuth
    lateinit var list_bill : ArrayList<bill>
    lateinit var billRecycleView : RecyclerView
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_transaction)

    billRecycleView = findViewById(R.id.list_bill)
    database = FirebaseDatabase.getInstance()
    auth = FirebaseAuth.getInstance()
    drawer_layout = findViewById(R.id.drawer_layout)
    nav_view = findViewById(R.id.nav_view)
    btnMenu = findViewById(R.id.btnMenu)
    nav_header = nav_view.getHeaderView(0)
    tvName = nav_header.findViewById(R.id.tvName)
    tvEmail = nav_header.findViewById(R.id.tvEmail)
    setUsername()
    setEmail()

    nav_view.setNavigationItemSelectedListener(this)
    btnMenuClicked()
    auth= FirebaseAuth.getInstance()
    billRecycleView.layoutManager= LinearLayoutManager(this)
    billRecycleView.setHasFixedSize(true)
    list_bill = arrayListOf<bill>()
    getTransaction()


}

fun getTransaction(){
    val uid = auth.currentUser!!.uid
    ref = database.getReference("Bill").child(uid)
    ref.addValueEventListener(object : ValueEventListener{
        override fun onDataChange(snapshot: DataSnapshot) {
            if (snapshot.exists()){
                for (data in snapshot.children){
                    val model = data.getValue(bill::class.java)
                    list_bill.add(model!!)
                }
                billRecycleView.adapter = Myadpater(list_bill)
            }
        }

        override fun onCancelled(error: DatabaseError) {
            TODO("Not yet implemented")
        }

    })
}

这是 Myadapter 类

class Myadpater(val list_bill: ArrayList<bill>) :
    RecyclerView.Adapter<Myadpater.MyViewHolder>() {
    class MyViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
        val category: TextView = itemView.findViewById(R.id.TCategory)
        val expense: TextView = itemView.findViewById(R.id.TExpense)
        val date :TextView = itemView.findViewById(R.id.TDate)

    }
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): MyViewHolder {
    val itemView =
        LayoutInflater.from(parent.context).inflate(R.layout.transaction_history, parent, false)
    return MyViewHolder(itemView)
}

override fun onBindViewHolder(holder: MyViewHolder, position: Int) {
    holder.category.text = list_bill[position].category
    holder.expense.text = list_bill[position].expense
    holder.date.text = list_bill[position].date
}

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

}

  class Myadpater(val list_bill: ArrayList<bill>) :
       RecyclerView.Adapter<Myadpater.MyViewHolder>() {
       class MyViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
         val category: TextView = itemView.findViewById(R.id.TCategory)
         val expense: TextView = itemView.findViewById(R.id.TExpense)
         val date :TextView = itemView.findViewById(R.id.TDate)

    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): MyViewHolder {
        val itemView =
            LayoutInflater.from(parent.context).inflate(R.layout.transaction_history, parent, false)
        return MyViewHolder(itemView)
    }

    override fun onBindViewHolder(holder: MyViewHolder, position: Int) {
        holder.category.text = list_bill[position].category
        holder.expense.text = list_bill[position].expense
        holder.date.text = list_bill[position].date
    }

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

}

在此处输入图像描述

这是我得到的错误

    E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.budget, PID: 5201
com.google.firebase.database.DatabaseException: Can't convert object of type java.lang.String to type com.example.budget.data.bill
    at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertBean(CustomClassMapper.java:436)
    at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.deserializeToClass(CustomClassMapper.java:232)
    at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertToCustomClass(CustomClassMapper.java:80)
    at com.google.firebase.database.DataSnapshot.getValue(DataSnapshot.java:203)
    at com.example.budget.TransactionActivity$getTransaction$1.onDataChange(TransactionActivity.kt:71)
    at com.google.firebase.database.core.ValueEventRegistration.fireEvent(ValueEventRegistration.java:75)
    at com.google.firebase.database.core.view.DataEvent.fire(DataEvent.java:63)
    at com.google.firebase.database.core.view.EventRaiser$1.run(EventRaiser.java:55)
    at android.os.Handler.handleCallback(Handler.java:938)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loop(Looper.java:223)
    at android.app.ActivityThread.main(ActivityThread.java:7656)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
4

1 回答 1

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当您使用以下参考时：

ref = database.getReference("Bill").child(uid)

并使用以下循环遍历 DataSnapshot：

for (data in snapshot.children){
    val model = data.getValue(bill::class.java)
    list_bill.add(model!!)
}

这意味着您正在尝试获取存在于 UID 节点中的每个子节点并将其转换为 type 的对象model。看到你的截图，我可以说UID节点下没有model对象，只有String对象。由于在 Kotlin 中无法将 String 转换为 type 的对象model，因此会出现上述错误。如果你想model在 UID 节点下有多个对象，那么你应该使用push()，每次添加数据时：

ref.push().setValue(yourModelObj).addOnCompleteListener(/* ... /*)
//  ^^^^^

您的新数据库架构将如下所示：

Firebase-root
  |
  --- Bill
       |
       --- KoqT...O6H3
             |
             --- $pushedId //Newly added level
                    |
                    --- categoryy: "food"
                    |
                    --- date: "22 Jul, 2021"
                    |
                    --- expense: "20"

要取回所有model对象，无需执行任何操作，您的实际代码将完美运行。

PS不要忘记删除现在存在的String值，否则，您将继续获得该异常。

于 2021-07-23T05:57:50.393 回答