无法反序列化 object.Can 无法将类型 java.lang.String 的对象转换为类型 com.example.quiz.models.Question（在字段 'questions.title' 中找到）

Question

我正在尝试从 Firestore 获取数据。但是出现错误：

java.lang.RuntimeException: Could not deserialize object. Can't convert object of type java.lang.String to type com.example.quiz.models.Question (found in field 'questions.title')

错误是在 setUpFirestore() 中发现的，并且是由于以下行：Log.d("DATA", value.toObjects(Quiz::class.java).toString()) {根据 logcat 错误}

我的主要活动：

    package com.example.quiz.activities

import android.content.Intent
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.util.Log
import android.view.MenuItem
import android.widget.Toast
import androidx.appcompat.app.ActionBarDrawerToggle
import androidx.recyclerview.widget.GridLayoutManager
import com.example.quiz.R
import com.example.quiz.adapters.QuizAdapter
import com.example.quiz.databinding.ActivityMainBinding
import com.example.quiz.models.Quiz
import com.google.android.material.datepicker.MaterialDatePicker
import com.google.firebase.firestore.DocumentSnapshot
import com.google.firebase.firestore.FirebaseFirestore
import java.text.SimpleDateFormat
import java.util.*

class MainActivity() : AppCompatActivity() {

    private lateinit var binding: ActivityMainBinding
    lateinit var actionBarDrawerToggle: ActionBarDrawerToggle
    lateinit var adapter: QuizAdapter
    private var quizList = mutableListOf<Quiz>()
    lateinit var firestore : FirebaseFirestore

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = ActivityMainBinding.inflate(layoutInflater)
        setContentView(binding.root)
        setUpViews()
    }

    fun setUpViews(){
        setUpFirestore()
        setUpDrawerLayout()
        setUpRecyclerView()
        setUpDatePicker()
    }

    private fun setUpDatePicker() {
        val btnDatePicker = binding.btnDatePicker
        btnDatePicker.setOnClickListener{
            val datePicker = MaterialDatePicker.Builder.datePicker().build()
            datePicker.show(supportFragmentManager,"DatePicker")
            datePicker.addOnPositiveButtonClickListener {
                Log.d("DATEPICKER",datePicker.headerText)
                val dateFormatter =  SimpleDateFormat("dd-mm-yyyy")
                val date = dateFormatter.format(Date(it))
                val intent = Intent(this,QuestionActivity::class.java)
                intent.putExtra("DATE",date)
                startActivity(intent)
            }
            datePicker.addOnNegativeButtonClickListener {
                Log.d("DATEPICKER",datePicker.headerText)
            }
            datePicker.addOnCancelListener {
                Log.d("DATEPICKER","Date Picker was cancelled")
            }
        }
    }

    private fun setUpFirestore() {
        firestore = FirebaseFirestore.getInstance()
        val collectionReference = firestore.collection("quizzes")
        collectionReference.addSnapshotListener{ value,error ->
            if(value == null || error != null){
                Toast.makeText(this,"Error fetching data",Toast.LENGTH_SHORT).show()
                return@addSnapshotListener
            }
            Log.d("DATA", value.toObjects(Quiz::class.java).toString())
            quizList.clear()
            quizList.addAll(value.toObjects(Quiz::class.java))
            adapter.notifyDataSetChanged()
        }
    }

    private fun setUpRecyclerView(){
        val quizRecyclerView = binding.quizRecyclerView
        adapter = QuizAdapter(this,quizList)
        quizRecyclerView.layoutManager = GridLayoutManager(this,2)
        quizRecyclerView.adapter = adapter
    }

    fun setUpDrawerLayout(){
        val appBar = binding.appBar
        val mainDrawer = binding.mainDrawer
        val navigationView = binding.navigationView
        setSupportActionBar(appBar)
        actionBarDrawerToggle = ActionBarDrawerToggle(this,mainDrawer,
            R.string.app_name,
            R.string.app_name
        )
        actionBarDrawerToggle.syncState()
        navigationView.setNavigationItemSelectedListener {
            val intent = Intent(this,ProfileActivity::class.java)
            startActivity(intent)
            mainDrawer.closeDrawers()
            true
        }
    }

    override fun onOptionsItemSelected(item: MenuItem): Boolean {
        if (actionBarDrawerToggle.onOptionsItemSelected(item)){
            return true
        }
        return super.onOptionsItemSelected(item)
    }
}

我的问题模型如下：

package com.example.quiz.models

data class Question(
    var description: String = "",
    var option1: String = "",
    var option2: String = "",
    var option3: String = "",
    var option4: String = "",
    var answer: String = "",
    var userAnswer:String=""
)

我的测验模型是-

package com.example.quiz.models

import com.google.firebase.auth.FirebaseAuth

data class Quiz(
    var id: String = "",
    var title: String = "",
    var questions: MutableMap<String, Question> = mutableMapOf()
)

数据库图片：

database image

logcat 错误是-

2022-04-24 17:19:04.678 12341-12341/com.example.quiz E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.quiz, PID: 12341
    java.lang.RuntimeException: Could not deserialize object. Can't convert object of type java.lang.String to type com.example.quiz.models.Question (found in field 'questions.title')
        at com.google.firebase.firestore.util.CustomClassMapper.deserializeError(CustomClassMapper.java:568)
        at com.google.firebase.firestore.util.CustomClassMapper.convertBean(CustomClassMapper.java:549)
        at com.google.firebase.firestore.util.CustomClassMapper.deserializeToClass(CustomClassMapper.java:258)
        at com.google.firebase.firestore.util.CustomClassMapper.deserializeToType(CustomClassMapper.java:194)
        at com.google.firebase.firestore.util.CustomClassMapper.deserializeToParameterizedType(CustomClassMapper.java:296)
        at com.google.firebase.firestore.util.CustomClassMapper.deserializeToType(CustomClassMapper.java:192)
        at com.google.firebase.firestore.util.CustomClassMapper.access0(CustomClassMapper.java:57)
        at com.google.firebase.firestore.util.CustomClassMapper$BeanMapper.deserialize(CustomClassMapper.java:775)
        at com.google.firebase.firestore.util.CustomClassMapper$BeanMapper.deserialize(CustomClassMapper.java:746)
        at com.google.firebase.firestore.util.CustomClassMapper.convertBean(CustomClassMapper.java:547)
        at com.google.firebase.firestore.util.CustomClassMapper.deserializeToClass(CustomClassMapper.java:258)
        at com.google.firebase.firestore.util.CustomClassMapper.convertToCustomClass(CustomClassMapper.java:103)
        at com.google.firebase.firestore.DocumentSnapshot.toObject(DocumentSnapshot.java:183)
        at com.google.firebase.firestore.QueryDocumentSnapshot.toObject(QueryDocumentSnapshot.java:116)
        at com.google.firebase.firestore.QuerySnapshot.toObjects(QuerySnapshot.java:184)
        at com.google.firebase.firestore.QuerySnapshot.toObjects(QuerySnapshot.java:166)
        at com.example.quiz.activities.MainActivity.setUpFirestore$lambda-4(MainActivity.kt:95)
        at com.example.quiz.activities.MainActivity.$r8$lambda$ALF8Ugv5XcVyBlrGHEr70w5PaxM(Unknown Source:0)
        at com.example.quiz.activities.MainActivity$$ExternalSyntheticLambda5.onEvent(Unknown Source:4)
        at com.google.firebase.firestore.Query.lambda$addSnapshotListenerInternal$com-google-firebase-firestore-Query(Query.java:1205)
        at com.google.firebase.firestore.Query$$ExternalSyntheticLambda2.onEvent(Unknown Source:6)
        at com.google.firebase.firestore.core.AsyncEventListener.lambda$onEvent[=17=]$com-google-firebase-firestore-core-AsyncEventListener(AsyncEventListener.java:42)
        at com.google.firebase.firestore.core.AsyncEventListener$$ExternalSyntheticLambda0.run(Unknown Source:6)
        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)

Answer 1

您遇到以下错误：

Could not deserialize object.Can't convert object of type java.lang.String to type com.example.quiz.models.Question (found in field 'questions.title')

因为使用这行代码时：

Log.d("DATA", value.toObjects(Quiz::class.java).toString())

这意味着您正在尝试将每个文档转换为 Quiz 类型的 object，这实际上是不可能的。为什么？因为每个文档应该包含一个 questions 数组，该数组应该由 only Question object 组成。但这并没有发生，因为该数组还包含一个名为 title 的字符串。正如我在您的测验 class 中看到的那样，标题字段应该是直接在文档中的字段，并且应该 而不是 出现在数组中。要解决此问题，您必须从数组中删除标题并将其添加为文档中的字段。

无法反序列化 object.Can 无法将类型 java.lang.String 的对象转换为类型 com.example.quiz.models.Question（在字段 'questions.title' 中找到）

Could not deserialize object.Can't convert object of type java.lang.String to type com.example.quiz.models.Question (found in field 'questions.title')

android

kotlin

firebase

google-cloud-platform

google-cloud-firestore