使用Kotlin检索数据时发生Firestore错误

Question

我正在尝试使用MVVM模式从Firebase Firestore检索数据。每次构建都会成功，但应用程序无法打开。我找不到代码中的错误。应用程序可以添加数据，但检索数据是个问题。请帮忙。谢谢

ViewModel

import android.util.Log
import androidx.lifecycle.LiveData
import androidx.lifecycle.MutableLiveData
import androidx.lifecycle.ViewModel
import com.google.firebase.firestore.FirebaseFirestore
import com.karuneshpalekar.firestorepagination.models.Note
import java.lang.Exception
class DataViewModel : ViewModel() {
companion object{
private const val  TAG =" VIEWMODEL"
}
private val db = FirebaseFirestore.getInstance()
private val noteref = db.collection("record")
private val _results = MutableLiveData<Exception>()
val results: LiveData<Exception>
get() = _results
private val _notes = MutableLiveData<List<Note>>()
val notes: LiveData<List<Note>>
get() = _notes
fun addData(note: Note) {
noteref.add(note).addOnCompleteListener {
if (it.isSuccessful) {
Log.w("TAG", "success")
_results.value = null
} else {
_results.value = it.exception
}
}
}
fun fetchData() {
noteref.addSnapshotListener{ snapshot,e->
if (e!=null){
Log.w(TAG,"Listen failed",e)
return@addSnapshotListener
}
if (snapshot != null) {
val items = mutableListOf<Note>()
for (docs in snapshot){
val notes  = docs.toObject(Note::class.java)
notes.let {
items.add(it)
}
_notes.value = items
}
}
}
}
}

适配器

import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.recyclerview.widget.RecyclerView
import com.karuneshpalekar.firestorepagination.R
import com.karuneshpalekar.firestorepagination.models.Note
import kotlinx.android.synthetic.main.list_item.view.*
class DataAdapter : RecyclerView.Adapter<RecyclerView.ViewHolder>() {
private var items= mutableListOf<Note>()
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder {
return DataViewHolder(
LayoutInflater.from(parent.context).inflate(R.layout.list_item, parent, false)
)
}
override fun getItemCount(): Int {
return items.size
}
override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
when (holder) {
is DataViewHolder -> {
holder.bind(items[position])
}
}

}
fun setNote(items:List<Note>){
this.items = items as MutableList<Note>
notifyDataSetChanged()
}

class DataViewHolder constructor(itemView: View) : RecyclerView.ViewHolder(itemView) {
private val textName = itemView.text_view_name
fun bind(note: Note) {
textName.text = note.name
}
}
}

碎片

import android.os.Bundle
import androidx.fragment.app.Fragment
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.lifecycle.Observer
import androidx.lifecycle.ViewModelProviders
import com.karuneshpalekar.firestorepagination.R
import kotlinx.android.synthetic.main.fragment_recyclerview.*

class RecyclerView : Fragment() {

private lateinit var viewModel: DataViewModel
private lateinit var dataadapter : DataAdapter
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
// Inflate the layout for this fragment
viewModel = ViewModelProviders.of(this).get(DataViewModel::class.java)
return inflater.inflate(R.layout.fragment_recyclerview, container, false)
}
override fun onActivityCreated(savedInstanceState: Bundle?) {
super.onActivityCreated(savedInstanceState)
recycler_view.apply {
dataadapter = DataAdapter()
adapter = dataadapter
}

viewModel.fetchData()
viewModel.notes.observe(viewLifecycleOwner, Observer {
dataadapter.setNote(it)
})
floating_btn_add.setOnClickListener {
DialogFragment().show(childFragmentManager, "")
}
}
}

DialogFragment-添加数据

class DialogFragment :DialogFragment(){
private lateinit var viewmodel:DataViewModel

override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
viewmodel = ViewModelProviders.of(this).get(DataViewModel::class.java)
return inflater.inflate(R.layout.fragment_dialog, container, false)
}
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setStyle(STYLE_NO_TITLE, android.R.style.Theme_DeviceDefault_Light_Dialog_MinWidth)
}
override fun onActivityCreated(savedInstanceState: Bundle?) {
super.onActivityCreated(savedInstanceState)
viewmodel.results.observe(viewLifecycleOwner, Observer {
val message = if (it == null) {
getString(R.string.name_added)
} else {
getString(R.string.name_error)
}
Toast.makeText(requireContext(), message, Toast.LENGTH_SHORT).show()
dismiss()
})
button_add.setOnClickListener {
val names = edit_text_name.text.toString().trim()
val note= Note("",names)
viewmodel.addData(note)
}
}
}

RecyclerView XML

<androidx.coordinatorlayout.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
xmlns:app="http://schemas.android.com/apk/res-auto"
tools:context=".ui.RecyclerView">
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/recycler_view"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:padding="@dimen/margin"
app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"
tools:listitem="@layout/list_item"
/>
<com.google.android.material.floatingactionbutton.FloatingActionButton
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/floating_btn_add"
app:fabSize="normal"
android:layout_gravity="bottom|end"
android:layout_margin="@dimen/margin"
/>

</androidx.coordinatorlayout.widget.CoordinatorLayout>

以上是我的项目的代码

Answer 1

代码中唯一缺少的错误是在Model类(即Note class(中没有进行null检查。