我得到了这个错误，但我无法解决它。 com.google.firebase.database.DatabaseException：无法将 java.lang.String 类型的对象转换为类型

Posted 2023-04-19

【中文标题】我得到了这个错误，但我无法解决它。 com.google.firebase.database.DatabaseException：无法将 java.lang.String 类型的对象转换为类型

【英文标题】：I got this error , but I can't solve it. com.google.firebase.database.DatabaseException: Can't convert object of type java.lang.String to type

【发布时间】：2021-09-30 05:25:29

【问题描述】：

com.google.firebase.database.DatabaseException: Can't convert an object of type java.lang.String to type，好像这个错误总是会发生但是我还是不知道怎么解决。

这是我展示 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
    

enter image description here

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)

【参考方案1】：

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 model 类型的对象。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 model 类型的对象，因此会出现上述错误。如果要在UID节点下有多个model对象，那么每次添加数据都应该使用push()：

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。

附：不要忘记删除当前存在的 String 值，否则，您将继续获得该异常。

【讨论】：

谢谢！！！男人，你帮了很多忙。现在完美运行。

很高兴听到这个消息，@kianhun4167chai