Android Paging 3 - 滚动和加载新页面时出现闪烁、故障或位置跳跃

Question

大家好，我正在使用 Android Jetpack Paging 库 3，我正在创建一个实现网络 + 数据库场景的新闻应用程序，并且我正在关注 google https://codelabs.developers.google.com/codelabs/android-paging 的代码实验室，我做的几乎就像在代码实验室中一样，我几乎匹配了示例中显示的所有操作https://github.com/android/architecture-components-samples/tree/main/PagingWithNetworkSample .
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，设置 View 模型。 ..
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，会获取新项目，并且再次出现故障和跳跃效果。
如果您能帮助我，我将不胜感激，我坐了三天，非常感谢您。这是我的代码 fragment :

@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>

新闻数据库Kt

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()
    }

远程调解员

    @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)
    }

}

分页存储库

 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
  }
}

博客查看模型

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()
}

政治 fragment Kotlin

      @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)

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)
    }
}

}
我试过设置 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，项目也会跳转。
在线刷新和加载视频
online loading and paging
online loading and paging(2)
离线刷新和加载视频
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 ，我可能做错了什么，当我刷新时只加载第一页的正确方法是什么？

Answer 1

只是从评论中跟进:
设置pageSize = 10解决了这个问题。
问题在于 pageSize太小，导致 PagingSource刷新未覆盖视口(viewport)的加载页面。由于源刷新替换列表并经过DiffUtil ，您需要提供 initialLoadSize足够大，以至于有一些重叠(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(bind)到足够靠近列表的边缘，它将自动触发 APPEND/PREPEND 加载。这就是默认 initialLoadSize 的原因。是 3 * pageSize ，但是如果您仍然遇到额外的负载，我建议您调整 prefetchDistance 或增加 initialLoadSize更远。