在使用 FirebaseRecyclerPagingAdapter 时，第二次单击 RecyclerView 中的项目时，片段显示为空
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【中文标题】在使用 FirebaseRecyclerPagingAdapter 时，第二次单击 RecyclerView 中的项目时，片段显示为空【英文标题】：Fragment shows up empty on the second click of an item from a RecyclerView while using FirebaseRecyclerPagingAdapter 【发布时间】：2021-11-10 08:41:44 【问题描述】：在我的应用程序中，当我单击 RecyclerView 中的一个项目（问题）时，它使用 FirebaseRecyclerPagingAdapter 对来自 Firebase 实时数据库的数据进行分页，它会显示有关在另一个片段中单击的项目的详细信息（使用导航组件）。这在第一次单击时可以正常工作，但是当我返回上一个片段并再次单击 RecyclerView 上的同一项目时，不会显示该项目的详细信息。
因为我使用安全参数将项目 id (issueId) 传递给下一个片段，它用于查询 firebase 实时数据库并检索要显示的详细信息，所以我决定在 onViewCreated( ) 只是为了确保在第二次单击时传递了项目 ID，并且正在从数据库中检索详细信息（添加问题的用户的名称），但只是不显示。然后，我注意到一个奇怪的行为。
在第一次单击时，项目 id 会记录到控制台，详细信息也会记录到控制台，并且片段会显示详细信息。但是，在第二次单击时，项目 id 被记录到控制台（显示项目 id 应该被传递），但详细信息没有记录到控制台，也没有显示在片段中（因此片段显示上空）。现在奇怪的部分是，当我导航回上一个片段时，我会看到显示了两次详细信息的日志。
我注意到的另一个奇怪的事情是，RecyclerView 上的每个项目都有这种奇怪的行为，除了最后一个项目。最后一个项目在第二次点击时显示其详细信息，但我点击的任何其他项目都不会。
我还注意到，当我返回导航时，日志会显示我之前点击过两次的每个项目的详细信息，即使我点击的是不同的项目
我将适配器从 FirebaseRecyclerPagingAdapter 更改为 FirebaseRecyclerAdapter，一切正常。当我改回使用 FirebaseRecyclerPagingAdapter 时，存在同样的问题。
这是我的代码中的错误还是 FirebaseRecyclerPagingAdapter 本身的错误。可能是什么问题，我可以做些什么来解决它？
下面是 FirebaseRecyclerPagingAdapter：
package com.colley.android.adapter
import android.annotation.SuppressLint
import android.content.Context
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.recyclerview.widget.RecyclerView
import com.bumptech.glide.Glide
import com.bumptech.glide.load.engine.DiskCacheStrategy
import com.colley.android.R
import com.colley.android.databinding.ItemIssueBinding
import com.colley.android.model.Issue
import com.colley.android.model.Profile
import com.firebase.ui.database.paging.DatabasePagingOptions
import com.firebase.ui.database.paging.FirebaseRecyclerPagingAdapter
import com.google.firebase.auth.FirebaseUser
import com.google.firebase.database.DataSnapshot
import com.google.firebase.database.DatabaseError
import com.google.firebase.database.ValueEventListener
import com.google.firebase.database.ktx.database
import com.google.firebase.database.ktx.getValue
import com.google.firebase.ktx.Firebase
class IssuesPagingAdapter(
options: DatabasePagingOptions<Issue>,
private val context: Context,
private val currentUser: FirebaseUser?,
private val clickListener: IssuePagingItemClickedListener
) : FirebaseRecyclerPagingAdapter<Issue, IssuePagingViewHolder>(options)
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): IssuePagingViewHolder
val viewBinding = ItemIssueBinding
.inflate(LayoutInflater.from(parent.context), parent, false)
return IssuePagingViewHolder(viewBinding)
override fun onBindViewHolder(viewHolder: IssuePagingViewHolder, position: Int, model: Issue)
viewHolder.bind(currentUser, model, context, clickListener)
interface IssuePagingItemClickedListener
fun onItemClick(issueId: String, view: View)
fun onItemLongCLicked(issueId: String, view: View)
fun onUserClicked(userId: String, view: View)
class IssuePagingViewHolder (private val itemBinding : ItemIssueBinding) : RecyclerView.ViewHolder(itemBinding.root)
@SuppressLint("SetTextI18n")
fun bind(
currentUser: FirebaseUser?,
issue: Issue, context: Context,
clickListener: IssuesPagingAdapter.IssuePagingItemClickedListener) = with(itemBinding)
//set issue title, body, timeStamp, contributions and endorsements count
issueTitleTextView.text = issue.title
issueBodyTextView.text = issue.body
issueTimeStampTextView.text = issue.timeStamp
contributionsTextView.text = issue.contributionsCount.toString()
endorsementTextView.text = issue.endorsementsCount.toString()
//check if userId is not null
issue.userId?.let userId ->
//retrieve user profile
Firebase.database.reference.child("profiles").child(userId)
.addListenerForSingleValueEvent(
object : ValueEventListener
override fun onDataChange(snapshot: DataSnapshot)
val profile = snapshot.getValue<Profile>()
if (profile != null)
//set the name of user who raised this issue
userNameTextView.text = profile.name
//set the school of the user who raised this issue
userSchoolTextView.text = profile.school
override fun onCancelled(error: DatabaseError)
)
//retrieve user photo
Firebase.database.reference.child("photos").child(userId)
.addListenerForSingleValueEvent(
object : ValueEventListener
override fun onDataChange(snapshot: DataSnapshot)
val photo = snapshot.getValue<String>()
//set photo
if (photo != null)
Glide.with(root.context).load(photo)
.diskCacheStrategy(DiskCacheStrategy.RESOURCE).into(userImageView)
else
Glide.with(root.context).load(R.drawable.ic_person).into(userImageView)
override fun onCancelled(error: DatabaseError)
)
root.setOnClickListener
if(issue.issueId != null)
clickListener.onItemClick(issue.issueId, it)
root.setOnLongClickListener
if(issue.issueId != null)
clickListener.onItemLongCLicked(issue.issueId, it)
true
userNameTextView.setOnClickListener
if(issue.userId != null)
clickListener.onUserClicked(issue.userId, it)
这是显示项目详细信息的片段：
package com.colley.android.view.fragment
import android.os.Bundle
import android.util.Log
import android.view.*
import android.view.View.GONE
import android.view.View.VISIBLE
import android.widget.Toast
import androidx.core.os.bundleOf
import androidx.fragment.app.Fragment
import androidx.navigation.fragment.findNavController
import androidx.navigation.fragment.navArgs
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.RecyclerView
import com.bumptech.glide.Glide
import com.colley.android.R
import com.colley.android.adapter.IssuesCommentsRecyclerAdapter
import com.colley.android.databinding.FragmentViewIssueBinding
import com.colley.android.model.Comment
import com.colley.android.model.Issue
import com.colley.android.model.Profile
import com.colley.android.view.dialog.IssueCommentBottomSheetDialogFragment
import com.firebase.ui.database.FirebaseRecyclerOptions
import com.firebase.ui.database.ObservableSnapshotArray
import com.google.firebase.auth.FirebaseAuth
import com.google.firebase.auth.FirebaseUser
import com.google.firebase.auth.ktx.auth
import com.google.firebase.database.*
import com.google.firebase.database.ktx.database
import com.google.firebase.database.ktx.getValue
import com.google.firebase.ktx.Firebase
class ViewIssueFragment :
Fragment(),
IssuesCommentsRecyclerAdapter.ItemClickedListener,
IssuesCommentsRecyclerAdapter.DataChangedListener
private val args: ViewIssueFragmentArgs by navArgs()
private var _binding: FragmentViewIssueBinding? = null
private val binding get() = _binding
private lateinit var dbRef: DatabaseReference
private lateinit var auth: FirebaseAuth
private lateinit var currentUser: FirebaseUser
private lateinit var recyclerView: RecyclerView
private lateinit var commentSheetDialog: IssueCommentBottomSheetDialogFragment
private var issue: Issue? = null
private var adapter: IssuesCommentsRecyclerAdapter? = null
private var manager: LinearLayoutManager? = null
private val uid: String
get() = currentUser.uid
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View?
_binding = FragmentViewIssueBinding.inflate(inflater, container, false)
recyclerView = binding?.issuesCommentsRecyclerView!!
return binding?.root
override fun onViewCreated(view: View, savedInstanceState: Bundle?)
super.onViewCreated(view, savedInstanceState)
//initialize Realtime Database
dbRef = Firebase.database.reference
//initialize authentication
auth = Firebase.auth
//initialize currentUser
currentUser = auth.currentUser!!
//log item id
Log.d("Log itemId", args.issueId)
//get a query reference to issue comments //order by time stamp
val commentsRef = dbRef.child("issues").child(args.issueId)
.child("comments").orderByChild("commentTimeStamp")
//the FirebaseRecyclerAdapter class and options come from the FirebaseUI library
//build an options to configure adapter. setQuery takes firebase query to listen to and a
//model class to which snapShots should be parsed
val options = FirebaseRecyclerOptions.Builder<Comment>()
.setQuery(commentsRef, Comment::class.java)
.build()
//initialize issue comments adapter
adapter = IssuesCommentsRecyclerAdapter(
options,
currentUser,
this,
this,
requireContext())
manager = LinearLayoutManager(requireContext())
//reversing layout and stacking fron end so that the most recent comments appear at the top
manager?.reverseLayout = true
manager?.stackFromEnd = true
recyclerView.layoutManager = manager
recyclerView.adapter = adapter
dbRef.child("issues").child(args.issueId).addValueEventListener(
object : ValueEventListener
override fun onDataChange(snapshot: DataSnapshot)
issue = snapshot.getValue<Issue>()
if(issue != null)
//listener for contrbutions count used to set count text
dbRef.child("issues").child(args.issueId)
.child("contributionsCount").addListenerForSingleValueEvent(
object : ValueEventListener
override fun onDataChange(snapshot: DataSnapshot)
val count = snapshot.getValue<Int>()
if(count != null)
binding?.contributionsTextView?.text = count.toString()
override fun onCancelled(error: DatabaseError)
)
//listener for endorsement counts used to set endorsement count text
dbRef.child("issues").child(args.issueId)
.child("endorsementsCount").addListenerForSingleValueEvent(
object : ValueEventListener
override fun onDataChange(snapshot: DataSnapshot)
val count = snapshot.getValue<Int>()
if(count != null)
binding?.endorsementTextView?.text = count.toString()
override fun onCancelled(error: DatabaseError)
)
//set issue title, body and time stamp, these don't need to change
binding?.issueTitleTextView?.text = issue?.title
binding?.issueBodyTextView?.text = issue?.body
binding?.issueTimeStampTextView?.text = issue?.timeStamp.toString()
//listener for user photo
dbRef.child("photos").child(issue?.userId.toString())
.addListenerForSingleValueEvent(
object : ValueEventListener
override fun onDataChange(snapshot: DataSnapshot)
val photo = snapshot.getValue<String>()
if(photo != null)
context?.let context -> binding?.userImageView?.let
imageView ->
Glide.with(context).load(photo).into(
imageView
)
else
context?.let context -> binding?.userImageView?.let
imageView ->
Glide.with(context).load(R.drawable.ic_profile).into(
imageView
)
override fun onCancelled(error: DatabaseError)
)
//listener for profile to set name and school
dbRef.child("profiles").child(issue?.userId.toString())
.addListenerForSingleValueEvent(
object : ValueEventListener
override fun onDataChange(snapshot: DataSnapshot)
val profile = snapshot.getValue<Profile>()
if (profile != null)
//log name details to console
profile.name?.let Log.d("Log Details", it)
binding?.userNameTextView?.text = profile.name
binding?.userSchoolTextView?.text = profile.school
override fun onCancelled(error: DatabaseError)
)
override fun onCancelled(error: DatabaseError)
)
binding?.commentLinearLayout?.setOnClickListener
commentSheetDialog = IssueCommentBottomSheetDialogFragment(
requireContext(),
requireView())
commentSheetDialog.arguments = bundleOf("issueIdKey" to args.issueId)
commentSheetDialog.show(parentFragmentManager, null)
binding?.endorseLinearLayout?.setOnClickListener
//update contributions count
dbRef.child("issues").child(args.issueId).child("endorsementsCount")
.runTransaction(
object : Transaction.Handler
override fun doTransaction(currentData: MutableData): Transaction.Result
//retrieve the current value of endorsement count at this location
var endorsementsCount = currentData.getValue<Int>()
if (endorsementsCount != null)
//increase the count by 1
endorsementsCount++
//reassign the value to reflect the new update
currentData.value = endorsementsCount
//set database issue value to the new update
return Transaction.success(currentData)
override fun onComplete(
error: DatabaseError?,
committed: Boolean,
currentData: DataSnapshot?
)
if (error == null && committed)
Toast.makeText(requireContext(), "Endorsed", Toast.LENGTH_SHORT)
.show()
)
//view profile when clicked
binding?.userImageView?.setOnClickListener
val action = issue?.userId?.let it1 ->
ViewIssueFragmentDirections.actionViewIssueFragmentToUserInfoFragment(it1)
if (action != null)
parentFragment?.findNavController()?.navigate(action)
//view user profile when clicked
binding?.userNameTextView?.setOnClickListener
val action = issue?.userId?.let it1 ->
ViewIssueFragmentDirections.actionViewIssueFragmentToUserInfoFragment(it1)
if (action != null)
parentFragment?.findNavController()?.navigate(action)
override fun onItemClick(comment: Comment, view: View)
//expand comment
override fun onItemLongCLicked(comment: Comment, view: View)
//create option to delete
//create option to respond
//view user profile
override fun onUserClicked(userId: String, view: View)
val action = ViewIssueFragmentDirections.actionViewIssueFragmentToUserInfoFragment(userId)
parentFragment?.findNavController()?.navigate(action)
override fun onStart()
super.onStart()
adapter?.startListening()
override fun onStop()
super.onStop()
adapter?.stopListening()
override fun onDestroy()
super.onDestroy()
_binding = null
override fun onDataAvailable(snapshotArray: ObservableSnapshotArray<Comment>)
//dismiss progress bar once snapshot is available
binding?.issuesCommentProgressBar?.visibility = GONE
//show that there are no comments if snapshot is empty else hide view
//show recycler view if snapshot is not empty else hide
if (snapshotArray.isEmpty())
binding?.noCommentsLayout?.visibility = VISIBLE
else
binding?.noCommentsLayout?.visibility = GONE
binding?.issuesCommentsRecyclerView?.visibility = VISIBLE
这是带有 recyclerView 的片段，显示了我如何初始化适配器：
package com.colley.android.view.fragment
import android.os.Bundle
import android.view.*
import android.view.View.GONE
import android.view.View.VISIBLE
import android.widget.Toast
import androidx.fragment.app.Fragment
import androidx.lifecycle.lifecycleScope
import androidx.navigation.fragment.findNavController
import androidx.paging.LoadState
import androidx.paging.PagingConfig
import androidx.recyclerview.widget.DiffUtil
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.RecyclerView
import androidx.swiperefreshlayout.widget.SwipeRefreshLayout
import com.colley.android.R
import com.colley.android.adapter.IssuesPagingAdapter
import com.colley.android.databinding.FragmentIssuesBinding
import com.colley.android.model.Issue
import com.firebase.ui.database.paging.DatabasePagingOptions
import com.google.firebase.auth.FirebaseAuth
import com.google.firebase.auth.FirebaseUser
import com.google.firebase.auth.ktx.auth
import com.google.firebase.database.DataSnapshot
import com.google.firebase.database.DatabaseReference
import com.google.firebase.database.ktx.database
import com.google.firebase.ktx.Firebase
import kotlinx.coroutines.flow.collectLatest
import kotlinx.coroutines.launch
class IssuesFragment :
Fragment(),
IssuesPagingAdapter.IssuePagingItemClickedListener
private var _binding: FragmentIssuesBinding? = null
private val binding get() = _binding!!
private lateinit var dbRef: DatabaseReference
private lateinit var auth: FirebaseAuth
private lateinit var currentUser: FirebaseUser
private var adapter: IssuesPagingAdapter? = null
private var manager: LinearLayoutManager? = null
private lateinit var recyclerView: RecyclerView
private lateinit var swipeRefreshLayout: SwipeRefreshLayout
private val uid: String
get() = currentUser.uid
override fun onCreate(savedInstanceState: Bundle?)
super.onCreate(savedInstanceState)
//fragment can participate in populating the options menu
setHasOptionsMenu(true)
//initialize Realtime Database
dbRef = Firebase.database.reference
//initialize authentication
auth = Firebase.auth
//initialize currentUser
currentUser = auth.currentUser!!
override fun onCreateOptionsMenu(menu: Menu, inflater: MenuInflater)
super.onCreateOptionsMenu(menu, inflater)
menu.clear()
inflater.inflate(R.menu.isssues_menu, menu)
override fun onOptionsItemSelected(item: MenuItem): Boolean
return when (item.itemId)
R.id.search_issues_menu_item ->
Toast.makeText(context, "Searching issues", Toast.LENGTH_LONG).show()
true
else -> super.onOptionsItemSelected(item)
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View?
_binding = FragmentIssuesBinding.inflate(inflater, container, false)
recyclerView = binding.issueRecyclerView
swipeRefreshLayout = binding.swipeRefreshLayout
return binding.root
override fun onViewCreated(view: View, savedInstanceState: Bundle?)
super.onViewCreated(view, savedInstanceState)
//get a query reference to issues
val issuesQuery = dbRef.child("issues")
//configuration for how the FirebaseRecyclerPagingAdapter should load pages
val config = PagingConfig(
pageSize = 30,
prefetchDistance = 15,
enablePlaceholders = false
)
//Options to configure an FirebasePagingAdapter
val options = DatabasePagingOptions.Builder<Issue>()
.setLifecycleOwner(viewLifecycleOwner)
.setQuery(issuesQuery, config, Issue::class.java)
.setDiffCallback(object : DiffUtil.ItemCallback<DataSnapshot>()
override fun areItemsTheSame(
oldItem: DataSnapshot,
newItem: DataSnapshot
): Boolean
return oldItem.getValue(Issue::class.java)?.issueId == newItem.getValue(Issue::class.java)?.issueId
override fun areContentsTheSame(
oldItem: DataSnapshot,
newItem: DataSnapshot
): Boolean
return oldItem.getValue(Issue::class.java) == newItem.getValue(Issue::class.java)
)
.build()
//instantiate adapter
adapter = IssuesPagingAdapter(
options,
requireContext(),
currentUser,
this)
//Perform some action every time data changes or when there is an error.
viewLifecycleOwner.lifecycleScope.launch
adapter?.loadStateFlow?.collectLatest loadStates ->
when (loadStates.refresh)
is LoadState.Error ->
// The initial load failed. Call the retry() method
// in order to retry the load operation.
Toast.makeText(context, "Error fetching issues! Retrying..", Toast.LENGTH_SHORT).show()
//display no posts available at the moment
binding.noIssuesLayout.visibility = VISIBLE
adapter?.retry()
is LoadState.Loading ->
// The initial Load has begun
// ...
swipeRefreshLayout.isRefreshing = true
is LoadState.NotLoading ->
// The previous load (either initial or additional) completed
swipeRefreshLayout.isRefreshing = false
//remove display no posts available at the moment
binding.noIssuesLayout.visibility = GONE
when (loadStates.append)
is LoadState.Error ->
// The additional load failed. Call the retry() method
// in order to retry the load operation.
adapter?.retry()
is LoadState.Loading ->
// The adapter has started to load an additional page
// ...
swipeRefreshLayout.isRefreshing = true
is LoadState.NotLoading ->
if (loadStates.append.endOfPaginationReached)
// The adapter has finished loading all of the data set
swipeRefreshLayout.isRefreshing = false
//set recycler view layout manager
manager = LinearLayoutManager(requireContext())
recyclerView.layoutManager = manager
//initialize adapter
recyclerView.adapter = adapter
swipeRefreshLayout.setOnRefreshListener
adapter?.refresh()
override fun onDestroy()
super.onDestroy()
_binding = null
//navigate to new fragment with issue id
override fun onItemClick(issueId: String, view: View)
val action = HomeFragmentDirections.actionHomeFragmentToViewIssueFragment(issueId)
parentFragment?.findNavController()?.navigate(action)
override fun onItemLongCLicked(issueId: String, view: View)
override fun onUserClicked(userId: String, view: View)
val action = HomeFragmentDirections.actionHomeFragmentToUserInfoFragment(userId)
parentFragment?.findNavController()?.navigate(action)
Before click
After first click
After second click
【问题讨论】：
如果您遇到问题，最好在发布问题时创建MCVE。您为此问题发布了近 700（七百）行行代码。人们需要解析和尝试在线调试的内容很多。请编辑您的问题并隔离问题，这样可以增加获得帮助的机会。 我的错！我发现了这个错误。我应该使用 addListenerForSingleValueEvent 而不是 addValueEventListener 从显示单击项目详细信息的片段中的数据库中查询项目详细信息（问题），否则删除 onStop() 中的 addValueEventListener 以便侦听器不再附加到数据库时我导航回上一个片段。 【参考方案1】：使用addListenerForSingleValueEvent 而不是addValueEventListener 从显示点击项目详细信息的片段中的数据库中查询项目详细信息（问题）。否则，删除onStop() 中的addValueEventListener，以便在导航回上一个片段时不再将侦听器附加到数据库。
【讨论】：
以上是关于在使用 FirebaseRecyclerPagingAdapter 时，第二次单击 RecyclerView 中的项目时，片段显示为空的主要内容，如果未能解决你的问题，请参考以下文章
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