Android Paging 3 - 滚动和加载新页面时出现闪烁、故障或位置跳跃
Posted
技术标签:
【中文标题】Android Paging 3 - 滚动和加载新页面时出现闪烁、故障或位置跳跃【英文标题】：Android Paging 3 - experiencing flickers, glitches or jumps in position when scrolling & loading new pages 【发布时间】：2021-06-12 02:59:19 【问题描述】：大家好，我正在使用 android Jetpack Paging library 3，我正在创建一个实现网络 + 数据库场景的新闻应用程序，并且我按照 google https://codelabs.developers.google.com/codelabs/android-paging 的 codelab 进行操作，我几乎就像在 codelab 中一样，我几乎匹配了所有示例https://github.com/android/architecture-components-samples/tree/main/PagingWithNetworkSample中显示的操作。
它几乎可以正常工作...但是我的后端响应是页面键控的，我的意思是响应带有新闻列表和下一页 url，远程调解器获取数据，填充数据库，设置存储库，viewmodel设置好了……
问题是： 当 recyclerview 加载数据时，会发生以下情况：recyclerview 闪烁，项目跳转，被删除，再次添加等等。 我不知道为什么 recyclerview 或其 itemanimator 会这样，看起来如此丑陋和故障。 更重要的是，当我滚动到列表的末尾时，新项目被提取，并且再次发生故障和跳跃效果。
如果你能帮助我，我将非常感激，我坐了三天，非常感谢你。这是我的代码sn-ps：
@Entity(tableName = "blogs")
data class Blog(
@PrimaryKey(autoGenerate = true)
val databaseid:Int,
@field:SerializedName("id")
val id: Int,
@field:SerializedName("title")
val title: String,
@field:SerializedName("image")
val image: String,
@field:SerializedName("date")
val date: String,
@field:SerializedName("share_link")
val shareLink: String,
@field:SerializedName("status")
val status: Int,
@field:SerializedName("url")
val url: String
)
var categoryId: Int? = null
var tagId: Int? = null
这是 DAO
@Insert(onConflict = OnConflictStrategy.REPLACE)
suspend fun insertAll(blogs: List<Blog>)
@Query("DELETE FROM blogs")
suspend fun deleteAllBlogs()
@Query("SELECT * FROM blogs WHERE categoryId= :categoryId ORDER BY id DESC")
fun getBlogsSourceUniversal(categoryId:Int?): PagingSource<Int, Blog>
@Query("SELECT * FROM blogs WHERE categoryId= :categoryId AND tagId= :tagId ORDER BY id DESC")
fun getBlogsSourceUniversalWithTags(categoryId:Int?,tagId:Int?): PagingSource<Int, Blog>
NewsDatabaseKt
abstract class NewsDatabaseKt : RoomDatabase()
abstract fun articleDAOKt(): ArticleDAOKt
abstract fun remoteKeyDao(): RemoteKeyDao
companion object
@Volatile
private var INSTANCE: NewsDatabaseKt? = null
fun getDatabase(context: Context): NewsDatabaseKt =
INSTANCE ?: synchronized(this)
INSTANCE ?: buildDatabase(context).also INSTANCE = it
private fun buildDatabase(context: Context) =
Room.databaseBuilder(context.applicationContext,
NewsDatabaseKt::class.java,
"news_database_kt")
.build()
远程调解器
@ExperimentalPagingApi
class BlogsRemoteMediator(private val categoryId: Int,
private val service: NewsAPIInterfaceKt,
private val newsDatabase: NewsDatabaseKt,
private val tagId : Int? = null ,
private val initialPage:Int = 1
) : RemoteMediator<Int, Blog>()
override suspend fun initialize(): InitializeAction
return InitializeAction.LAUNCH_INITIAL_REFRESH
override suspend fun load(loadType: LoadType, state: PagingState<Int, Blog>): MediatorResult
try
val page = when (loadType)
REFRESH ->
initialPage
PREPEND ->
return MediatorResult.Success(endOfPaginationReached = true)
APPEND ->
val remoteKey = newsDatabase.withTransaction
newsDatabase.remoteKeyDao().remoteKeyByLatest(categoryId.toString())
if(remoteKey.nextPageKey == null)
return MediatorResult.Success(endOfPaginationReached = true)
remoteKey.nextPageKey.toInt()
val apiResponse =
if(tagId == null)
service.getCategoryResponsePage(RU, categoryId, page.toString())
else
service.getCategoryTagResponsePage(RU,categoryId,tagId,page.toString())
val blogs = apiResponse.blogs
val endOfPaginationReached = blogs.size < state.config.pageSize
newsDatabase.withTransaction
// clear all tables in the database
if (loadType == LoadType.REFRESH)
newsDatabase.remoteKeyDao().deleteByLatest(categoryId.toString())
if(tagId == null)
newsDatabase.articleDAOKt().clearBlogsByCatId(categoryId)
else
newsDatabase.articleDAOKt().clearBlogsByCatId(categoryId,tagId)
blogs.map blog ->
blog.categoryId = categoryId
if(tagId != null)
blog.tagId = tagId
newsDatabase.remoteKeyDao().insert(LatestRemoteKey(categoryId.toString(),
apiResponse.nextPageParam))
newsDatabase.articleDAOKt().insertAll(blogs)
return MediatorResult.Success(
endOfPaginationReached = endOfPaginationReached
)
catch (exception: IOException)
return MediatorResult.Error(exception)
catch (exception: HttpException)
return MediatorResult.Error(exception)
PagingRepository
class PagingRepository(
private val service: NewsAPIInterfaceKt,
private val databaseKt: NewsDatabaseKt
)
@ExperimentalPagingApi
fun getBlogsResultStreamUniversal(int: Int, tagId : Int? = null) : Flow<PagingData<Blog>>
val pagingSourceFactory =
if(tagId == null)
databaseKt.articleDAOKt().getBlogsSourceUniversal(int)
else databaseKt.articleDAOKt().getBlogsSourceUniversalWithTags(int,tagId)
return Pager(
config = PagingConfig(
pageSize = 1
)
,remoteMediator =
BlogsRemoteMediator(int, service, databaseKt,tagId)
,pagingSourceFactory = pagingSourceFactory
).flow
博客视图模型
class BlogsViewModel(private val repository: PagingRepository):ViewModel()
private var currentResultUiModel: Flow<PagingData<UiModel.BlogModel>>? = null
private var categoryId:Int?=null
@ExperimentalPagingApi
fun getBlogsUniversalWithUiModel(int: Int, tagId : Int? = null):
Flow<PagingData<UiModel.BlogModel>>
val lastResult = currentResultUiModel
if(lastResult != null && int == categoryId)
return lastResult
val newResult: Flow<PagingData<UiModel.BlogModel>> =
repository.getBlogsResultStreamUniversal(int, tagId)
.map pagingData -> pagingData.map UiModel.BlogModel(it)
.cachedIn(viewModelScope)
currentResultUiModel = newResult
categoryId = int
return newResult
sealed class UiModel
data class BlogModel(val blog: Blog) : UiModel()
PoliticsFragmentKotlin
@ExperimentalPagingApi
class PoliticsFragmentKotlin : Fragment()
private lateinit var recyclerView: RecyclerView
private lateinit var pagedBlogsAdapter:BlogsAdapter
lateinit var viewModelKt: BlogsViewModel
lateinit var viewModel:NewsViewModel
private var searchJob: Job? = null
@ExperimentalPagingApi
private fun loadData(categoryId:Int, tagId : Int? = null)
searchJob?.cancel()
searchJob = lifecycleScope.launch
viewModelKt.getBlogsUniversalWithUiModel(categoryId, tagId).collectLatest
pagedBlogsAdapter.submitData(it)
@ExperimentalPagingApi
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?): View?
val view = inflater.inflate(R.layout.fragment_blogs, container, false)
viewModelKt = ViewModelProvider(requireActivity(),Injection.provideViewModelFactory(requireContext())).get(BlogsViewModel::class.java)
viewModel = ViewModelProvider(requireActivity()).get(NewsViewModel::class.java)
pagedBlogsAdapter = BlogsAdapter(context,viewModel)
val decoration = DividerItemDecoration(context, DividerItemDecoration.VERTICAL)
recyclerView = view.findViewById(R.id.politics_recyclerView)
recyclerView.addItemDecoration(decoration)
initAdapter()
loadData(categoryId)
initLoad()
return view
private fun initLoad()
lifecycleScope.launchWhenCreated
Log.d("meylis", "lqunched loadstate scope")
pagedBlogsAdapter.loadStateFlow
// Only emit when REFRESH LoadState for RemoteMediator changes.
.distinctUntilChangedBy it.refresh
// Only react to cases where Remote REFRESH completes i.e., NotLoading.
.filter it.refresh is LoadState.NotLoading
.collect recyclerView.scrollToPosition(0)
private fun initAdapter()
recyclerView.adapter = pagedBlogsAdapter.withLoadStateHeaderAndFooter(
header = BlogsLoadStateAdapter pagedBlogsAdapter.retry() ,
footer = BlogsLoadStateAdapter pagedBlogsAdapter.retry()
)
lifecycleScope.launchWhenCreated
pagedBlogsAdapter.loadStateFlow.collectLatest
swipeRefreshLayout.isRefreshing = it.refresh is LoadState.Loading
pagedBlogsAdapter.addLoadStateListener loadState ->
// Only show the list if refresh succeeds.
recyclerView.isVisible = loadState.source.refresh is LoadState.NotLoading
// Show loading spinner during initial load or refresh.
progressBar.isVisible = loadState.source.refresh is LoadState.Loading
// Show the retry state if initial load or refresh fails.
retryButton.isVisible = loadState.source.refresh is LoadState.Error
// Toast on any error, regardless of whether it came from RemoteMediator or PagingSource
val errorState = loadState.source.append as? LoadState.Error
?: loadState.source.prepend as? LoadState.Error
?: loadState.append as? LoadState.Error
?: loadState.prepend as? LoadState.Error
errorState?.let
Toast.makeText(context, "\uD83D\uDE28 Wooops $it.error", Toast.LENGTH_LONG
).show()
companion object
@JvmStatic
fun newInstance(categoryId: Int, tags : ArrayList<Tag>): PoliticsFragmentKotlin
val args = Bundle()
args.putInt(URL, categoryId)
args.putSerializable(TAGS,tags)
val fragmentKotlin = PoliticsFragmentKotlin()
fragmentKotlin.arguments = args
Log.d("meylis", "created instance")
return fragmentKotlin
博客适配器
class BlogsAdapter(var context: Context?, var newsViewModel:NewsViewModel) :
PagingDataAdapter<BlogsViewModel.UiModel.BlogModel, RecyclerView.ViewHolder>
(REPO_COMPARATOR)
private val VIEW = 10
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder
return when (viewType)
VIEW -> MyViewHolder(LayoutInflater.from(parent.context).inflate(R.layout.card_layout, parent, false))
override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int)
val uiModel = getItem(position)
if(uiModel == null)
if(uiModel is BlogsViewModel.UiModel.BlogModel)(holder as MyViewHolder).bind(null)
if(uiModel is BlogsViewModel.UiModel.BlogModel)(holder as
MyViewHolder).bind(uiModel.blog)
override fun getItemViewType(position: Int): Int
return VIEW
companion object
private val REPO_COMPARATOR = object : DiffUtil.ItemCallback<BlogsViewModel.UiModel.BlogModel>()
override fun areItemsTheSame(oldItem: BlogsViewModel.UiModel.BlogModel, newItem: BlogsViewModel.UiModel.BlogModel): Boolean =
oldItem.blog.title == newItem.blog.title
override fun areContentsTheSame(oldItem: BlogsViewModel.UiModel.BlogModel, newItem: BlogsViewModel.UiModel.BlogModel): Boolean =
oldItem == newItem
MyViewHolder
class MyViewHolder(var container: View) : RecyclerView.ViewHolder(container)
var cv: CardView
@JvmField
var mArticle: TextView
var date: TextView? = null
@JvmField
var time: TextView
@JvmField
var articleImg: ImageView
@JvmField
var shareView: View
var button: MaterialButton? = null
@JvmField
var checkBox: CheckBox
var progressBar: ProgressBar
private var blog:Blog? = null
init
cv = container.findViewById<View>(R.id.cardvmain) as CardView
mArticle = container.findViewById<View>(R.id.article) as TextView
articleImg = container.findViewById<View>(R.id.imgvmain) as ImageView
//button = (MaterialButton) itemView.findViewById(R.id.sharemain);
checkBox = container.findViewById<View>(R.id.checkboxmain) as CheckBox
time = container.findViewById(R.id.card_time)
shareView = container.findViewById(R.id.shareView)
progressBar = container.findViewById(R.id.blog_progress)
fun bind(blog: Blog?)
if(blog == null)
mArticle.text = "loading"
time.text = "loading"
articleImg.visibility = View.GONE
else
this.blog = blog
mArticle.text = blog.title
time.text = blog.date
if (blog.image.startsWith("http"))
articleImg.visibility = View.VISIBLE
val options: RequestOptions = RequestOptions()
.centerCrop()
.priority(Priority.HIGH)
GlideImageLoader(articleImg,
progressBar).load(blog.image, options)
else
articleImg.visibility = View.GONE
NewsApi接口
interface NewsAPIInterfaceKt
@GET("sort?")
suspend fun getCategoryResponsePage(@Header("Language") language: String, @Query("category")
categoryId: Int, @Query("page") pageNumber: String): BlogsResponse
@GET("sort?")
suspend fun getCategoryTagResponsePage(@Header("Language") language: String,
@Query("category") categoryId: Int,@Query("tag") tagId:Int, @Query("page") pageNumber: String)
:BlogsResponse
companion object
fun create(): NewsAPIInterfaceKt
val logger = HttpLoggingInterceptor()
logger.level = HttpLoggingInterceptor.Level.BASIC
val okHttpClient = UnsafeOkHttpClient.getUnsafeOkHttpClient()
return Retrofit.Builder()
.baseUrl(BASE_URL)
.client(okHttpClient)
.addConverterFactory(GsonConverterFactory.create())
.build()
.create(NewsAPIInterfaceKt::class.java)
我尝试设置 initialLoadSize = 1 但问题依然存在
编辑：感谢您的回答@dlam，是的，确实如此，我的网络 API 返回按 id 排序的结果列表。顺便说一句，当应用程序脱机运行时，项目也会发生这种跳转。
在线刷新和加载时的视频
online loading and paging
online loading and paging(2)
离线刷新和加载时的视频
offline loading and refreshing
再次感谢，这是我的要点链接https://gist.github.com/Aydogdyshka/7ca3eb654adb91477a42128de2f06ea9
编辑 非常感谢@dlam，当我设置 pageSize=10 时，跳转消失了……然后我想起了为什么我首先设置 pageSize=1……当我刷新时，加载了 3 x pageSize 的项目，即使我覆盖了 initialLoadSize = 10 ，刷新后它仍然加载 3 x pageSize 调用 append 2x ，我做错了什么，当我刷新时只加载第一页的正确方法是什么？
【问题讨论】：
您的网络 API 是否返回按 id 排序的结果？如果可能的话，你能分享一个项目跳跃的视频吗？PagingSource 和 RemoteMediator 加载的页面日志也很有帮助。你可能想把它放在一个要点中，因为它可能很长。 @dlam，是的，我的网络响应返回按 id 排序的结果。我还附上了我的问题的视频和要点链接 您可以尝试将您的pageSize 放大吗？或者至少更改initialPageSize。它应该覆盖 > viewport * 2，所以在你的情况下至少 8，也许尝试pageSize = 10？当您刷新时，它会替换列表并通过将两个列表传递给DiffUtil 来恢复位置。默认情况下，Room 的PagingSource 根据最后绑定位置选择索引，并根据pageSize 选择偏移量。为了在正确的位置附近加载刷新并在更新中流畅地进行动画处理，pageSize 必须足够大。
@dlam, yasss, 它起作用了）我设置了 pageSize=10 ，非常感谢，跳跃已经消失了……然后我想起了为什么我首先设置 pageSize=1 ……当我刷新，即使我覆盖了initialLoadSize = 10，也会加载3xpageSize的项目，刷新后它仍然加载3 x pageSize调用append 2x，我做错了什么？
如果你查看 PagingConfig 源代码，它会说参数 pageSize 和 initialLoadSize 可以被忽略。所以调整这两个参数并不是 100% 的解决方案。 Note: [initialLoadSize] is used to inform [PagingSource.LoadParams.loadSize], but is not enforced. A [PagingSource] may completely ignore this value and still return a valid initial [Page][PagingSource.LoadResult.Page].
【参考方案1】：
刚刚从 cmets 跟进：
设置pageSize = 10 解决了这个问题。
问题在于pageSize 太小，导致PagingSource 刷新加载未覆盖视口的页面。由于源刷新会替换列表并通过DiffUtil，因此您需要提供足够大的initialLoadSize，以便有一些重叠（否则滚动位置会丢失）。
顺便说一句 - 分页会根据 PagingConfig.prefetchDistance 自动加载附加数据。如果RecyclerView 将项目绑定到足够靠近列表的边缘，它将自动触发 APPEND / PREPEND 加载。这就是为什么 initialLoadSize 的默认值是 3 * pageSize 的原因，但是如果您仍然遇到额外的负载，我建议您调整 prefetchDistance，或者进一步增加 initialLoadSize。
【讨论】：
嗨，我仍然有附加附加负载的问题，当我将 initialLoadSize 设置为小于页面大小时，应用程序崩溃，当我将其设置为 initialLoadSize = pageSize 时，它仍然附加 2 次，我试过了prefetchDistance 的值不同，但问题仍然存在，我该怎么办？感谢您的帮助 屏幕上一次可以看到多少个项目？当 recyclerview 绑定它们时，分页将自动获取项目。页面获取由 prefetchDistance 根据最近对PagingDataAdapter.get(index) 的调用触发。
如果您将initialLoadSize 设置为小于pageSize，应用程序可能会崩溃，因为这是一个无效的PagingConfig，您是否阅读了抛出的异常消息？
屏幕上一次可见 4 个项目，我尝试将 initialLoadSize 设置为更大，并且小于 page 但它会使应用程序崩溃，我尝试将预取距离设置为 1，但它仍会加载额外的 2 个页面
闪烁问题如何？我遇到了类似的问题，但闪烁只发生在adapter.refresh() 的第一项上【参考方案2】：
recyclerview 闪烁，因为您从 dao 获得的项目与从网络响应的顺序不同。 我会建议你我的解决方案。 我们将按主键、databaseid、降序从数据库 order 中获取项目。 首先删除自动生成=真。 我们将手动设置 databaseid，按照我们从网络获取项目的顺序。
接下来让我们编辑 remoteMediator 加载函数。
when (loadType)
LoadType.PREPEND ->
blogs.map
val databaseid = getFirstBlogDatabaseId(state)?.databaseid?:0
movies.forEachIndexed
index, blog ->
blog.databaseid = roomId - (movies.size -index.toLong())
LoadType.APPEND ->
val roomId = getLastBlogDatabaseId(state)?.databaseid ?:0
blogs.forEachIndexed
index, blog ->
blog.databaseid = roomId + index.toLong() + 1
LoadType.REFRESH ->
blogs.forEachIndexed
index, blog ->
blog.databaseid = index.toLong()
private fun getFirstBlogDatabaseId(state: PagingState<Int, Blog>): Blog?
return state.pages.firstOrNull it.data.isNotEmpty() ?.data?.firstOrNull()
private fun getLastBlogDatabaseId(state: PagingState<Int, Blog>): Blog?
return state.lastItemOrNull()
【讨论】：
以上是关于Android Paging 3 - 滚动和加载新页面时出现闪烁、故障或位置跳跃的主要内容，如果未能解决你的问题，请参考以下文章
Android Paging 库不会触发 loadAfter()
Jetpack Compose 无限加载列表（滚到底部自动加载更多）
将 Paging 3 alpha 更新为稳定导致索引问题 Android