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,我正在关注 google 的 Codelab https://codelabs.developers.google.com/codelabs/android-paging ,我的做法几乎就像在 Codelab 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。
它几乎按预期工作...但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,远程中介获取数据,填充数据库,设置存储库,设置视图模型...
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 的行为如此,看起来如此丑陋和故障。 更重要的是,当我滚动到列表末尾时,会获取新项目,并且再次发生故障和跳跃效果。
如果您能帮助我,我将非常感激,我已经坐了三天了,非常感谢您提前。这是我的代码片段:
@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()
}
远程中介器
@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)
}
}
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FragmentKotlin
@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
}
}
我的ViewHolder
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,当应用程序离线运行时,项目也会进行此跳转。
在线刷新加载视频
离线刷新和加载时的视频
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,跳跃消失了...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,它仍然加载3 x pageSize,在刷新后调用append 2x次,我可能做错了什么,刷新时仅加载第一页的正确方法是什么?
只是从评论中跟进:
设置
pageSize = 10
解决了该问题。
问题在于
pageSize
太小,导致 PagingSource
刷新未覆盖视口的加载页面。由于源刷新会替换列表并遍历 DiffUtil
,因此您需要提供足够大的 initialLoadSize
,以便有一些重叠(否则滚动位置将丢失)。
顺便说一句 - 分页根据
PagingConfig.prefetchDistance
自动加载附加数据。如果 RecyclerView
绑定的项目足够靠近列表边缘,它将自动触发 APPEND / PREPEND 加载。这就是为什么 initialLoadSize
的默认值为 3 * pageSize
,但如果您仍然遇到额外负载,我建议调整 prefetchDistance,或进一步增加 initialLoadSize
。
config = PagingConfig(
pageSize = PAGE_SIZE,
enablePlaceholders = true,
prefetchDistance = 3* PAGE_SIZE,
initialLoadSize = 2*PAGE_SIZE,
)
确保enablePlaceholders设置为true并将页面大小设置为10到20左右
recyclerview 闪烁,因为您从 dao 获得的项目与网络响应的顺序不同。 我会建议你我的解决方案。 我们将从数据库中按主键、databaseid、降序顺序获取项目。 首先删除 auto generated = true。 我们将手动设置数据库ID,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()
}
如果回收器视图从末尾开始堆叠,这实际上不起作用。
androidx.recyclerview.widget.RecyclerView
中使用的值。
app:stackFromEnd="true"
有什么想法可以解决这个问题吗?谢谢你