官方分页工具, 确实香. 但数据源不开放, 无法随意增删改操作; 只能借助 Room; 但列表数据不一定都要用 Room吧;
如果偏查询的分页数据用 Paging3 ; 其他一概用 老Adapter; 这倒也算个方案. [苦笑]
官方 Pagings 优势:
RecyclerView
适配器,会在用户滚动到已加载数据的末尾时自动请求数据。LiveData
和 RxJava 的一流支持。导包:
dependencies {
val paging_version = "3.0.0"
//唯一必导包
implementation("androidx.paging:paging-runtime:$paging_version")
// 测试用
testImplementation("androidx.paging:paging-common:$paging_version")
// optional - RxJava2 support
implementation("androidx.paging:paging-rxjava2:$paging_version")
// optional - RxJava3 support
implementation("androidx.paging:paging-rxjava3:$paging_version")
// 适配 Guava 库 - 高效java扩展库
implementation("androidx.paging:paging-guava:$paging_version")
// 适配 Jetpack Compose - 代码构建View; 干掉 layout
implementation("androidx.paging:paging-compose:1.0.0-alpha09")
}
1. 简单使用:
1.1 数据源 PagingSource
自定义数据源, 继承 PagingSource
它有两个泛型参数, 1. 页码key, 没有特殊需求的话一般就是 Int 类型; 2.集合实体类型
重写两个方法: 1.load() 加载数据的方法; 2.getRefreshKey 初始加载的页码; 暂且返回 1 或 null
LoadResult.Page 后面再讲;
class DynamicDataSource: PagingSource
//模拟最大页码
private var maxPage = 2
//模拟数据
private fun fetchItems(startPosition: Int, pageSize: Int): MutableList<DynamicTwo> {
Log.d("ppppppppppppppppppppp", "startPosition=${startPosition};;;pageSize=${pageSize}")
val list: MutableList<DynamicTwo> = ArrayList()
for (i in startPosition until startPosition + pageSize) {
val concert = DynamicTwo()
concert.title = "我是标题${i}"
concert.newsInfo = "我是内容${i}"
concert.nickName = "小王${i}"
list.add(concert)
}
return list
}
override fun getRefreshKey(state: PagingState<Int, DynamicTwo>): Int? = null
override suspend fun load(params: LoadParams<Int>): LoadResult<Int, DynamicTwo> {
val nextPageNumber = params.key ?: 1
val size = params.loadSize
Log.d("ppppppppppppppppppppp", "nextPageNumber=${nextPageNumber};;;size=${size}")
val response = fetchItems((nextPageNumber-1) \* size, size)
return LoadResult.Page(
data = response,
prevKey = null, // Only paging forward. 只向后加载就给 null
//nextKey 下一页页码; 尾页给 null; 否则当前页码加1
nextKey = if(nextPageNumber >= maxPage) null else (nextPageNumber + 1)
)
}
}
1.2 ViewModel
代码比较简单. 内容我们一会再讲
class DynamicPagingModel(application: Application) : AndroidViewModel(application) {
val flow = Pager(
//配置
PagingConfig(pageSize = 10, prefetchDistance = 2,initialLoadSize = 10)
) {
//我们自定义的数据源
DynamicDataSource()
}.flow
.cachedIn(viewModelScope)
}
1.3 前台使用:
初始化 Adapter 及 RecycleView
mViewModel?.flow?.collectLatest 绑定监听, 然后通过 submitData() 刷新列表;
mAdapter = SimplePagingAdapter(R.layout.item_dynamic_img_two, null)
mDataBind.rvRecycle.let {
it.layoutManager = LinearLayoutManager(mActivity)
it.adapter = mAdapter
}
//Activity 用 lifecycleScope
//Fragments 用 viewLifecycleOwner.lifecycleScope
viewLifecycleOwner.lifecycleScope.launchWhenCreated {
mViewModel?.flow?.collectLatest {
mAdapter.submitData(it)
}
}
1.4 Adapter
必须继承 paging 的 PagingDataAdapter
DiffCallback() 或 handler NewViewHolder 不了解的可以看我的 ListAdapter 封装系列
open class SimplePagingAdapter(
private val layout: Int,
protected val handler: BaseHandler? = null
) :
PagingDataAdapter
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder {
return NewViewHolder(
DataBindingUtil.inflate(
LayoutInflater.from(parent.context), layout, parent, false
), handler
)
}
override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
if(holder is NewViewHolder){
holder.bind(getItem(position))
}
}
}
over 简单的分页模拟数据已完成;
2. LoadResult
它是一个密封类; 它表示加载操作的结果;
2.1 LoadResult.Error
表示加载失败; 需提供 Throwable 对象.
public data class Error
val throwable: Throwable
) : LoadResult
可用于:
2.1 LoadResult.Page
表示加载成功;
参数:
data 数据集合;
prevKey 前页页码 key; //向下一页加载 给null
nextKey 后页页码 key; //向上一页加载 给null
public data class Page
/**
* Loaded data
*/
val data: List
/**
* [Key] for previous page if more data can be loaded in that direction, `null`
* otherwise.
*/
val prevKey: Key?,
/**
* [Key] for next page if more data can be loaded in that direction, `null` otherwise.
*/
val nextKey: Key?,
/**
* Optional count of items before the loaded data.
*/
@IntRange(from = COUNT_UNDEFINED.toLong())
val itemsBefore: Int = COUNT_UNDEFINED,
/**
* Optional count of items after the loaded data.
*/
@IntRange(from = COUNT_UNDEFINED.toLong())
val itemsAfter: Int = COUNT_UNDEFINED
) : LoadResult
3.PagingConfig
分页配置
参数:
pageSize: 每页容量
prefetchDistance: 当RecycleView 滑动到底部时, 会自动加载下一页. 如果能提前预加载, 可以省去部分等待加载的时间.
prefetchDistance 就是距离底部提前加载的距离. 默认 = pageSize; = 0 时将不会加载更多
enablePlaceholders: 允许使用占位符. 想了解的点这里
initialLoadSize: 初始加载数量, 默认 = pageSize * 3
maxSize: 似乎意义没有那么简单. 还没看源码,不清楚; 不能 < pageSize + prefetchDistance * 2****
jumpThreshold: 某阈值! 好吧我摊牌了, 我不知道. [奸笑]
4.监听加载状态:
LoadState: 表示加载状态密封类;
LoadState.NotLoading: 加载完毕, 并且界面也已相应更新
LoadState.Error: 加载失败.
LoadState.Loading: 正在加载..
lifecycleScope.launch {
mAdapter.loadStateFlow.collectLatest { loadStates ->
when(loadStates.refresh){
is LoadState.Loading -> {
Log.d("pppppppppppppp", "加载中")
}
is LoadState.Error -> {
Log.d("pppppppppppppp", "加载失败")
}
is LoadState.NotLoading -> {
Log.d("pppppppppppppp", "完事了")
}
else -> {
Log.d("pppppppppppppp", "这是啥啊")
}
}
}
//或者:
mAdapter.addLoadStateListener { ... }
}
5. 状态适配器 LoadStateAdapter
用于直接在显示的分页数据列表中呈现加载状态。 例如: 尾部显示 正在加载, 加载失败, 没有更多等;
5.1 自定义 MyLoadStateAdapter 继承 LoadStateAdapter
重写 onCreateViewHolder, onBindViewHolder
retry: 如果加载失败, 想要重试, 则提供该高阶函数参数; 否则不需要它
class MyLoadStateAdapter(
/**
* 当下一页加载失败时, 继续尝试加载下一页;
*/
private val retry: () -> Unit
) : LoadStateAdapter
override fun onCreateViewHolder(
parent: ViewGroup,
loadState: LoadState
) = LoadStateViewHolder(parent, retry)
override fun onBindViewHolder(
holder: LoadStateViewHolder,
loadState: LoadState
) = holder.bind(loadState)
}
5.2 自定义 LoadStateViewHolder
功能:
class LoadStateViewHolder (
parent: ViewGroup,
retry: () -> Unit
) : RecyclerView.ViewHolder(
LayoutInflater.from(parent.context)
.inflate(R.layout.view_loading_more, parent, false)
) {
private val binding = ViewLoadingMoreBinding.bind(itemView)
init {
//当点击重试按钮时, 调用 PagingDataAdapter 的 retry() 重新尝试加载
binding.btnLoadingRetry.setOnClickListener {
retry()
}
}
fun bind(loadState: LoadState) {
// 当加载失败时.
if(loadState is LoadState.Error){
// 将没有更多封装成 NoMoreException; 此时显示没有更多 View
if(loadState.error is NoMoreException){
hideNoMoreUi(false) //显示 没有更多 View
hideErrUi(true) //隐藏 失败 View
}else{
hideNoMoreUi(true)
hideErrUi(false, loadState.error.message) //显示失败 View时, 填充错误 msg
}
}else{
hideNoMoreUi(true)
hideErrUi(true)
}
//加载中..
binding.pbLoadingBar.visibility = if(loadState is LoadState.Loading){
View.VISIBLE
}else{
View.GONE
}
}
/\*\*
\* 隐藏没有更多View;
\*/
private fun hideNoMoreUi(hide: Boolean){
if(hide){
binding.tvLoadingHint.visibility = View.GONE
}else{
binding.tvLoadingHint.visibility = View.VISIBLE
}
}
/\*\*
\* 隐藏 加载失败View;
\*/
private fun hideErrUi(hide: Boolean, msg: String? = null){
if(hide){
binding.tvLoadingError.visibility = View.GONE
binding.btnLoadingRetry.visibility = View.GONE
}else{
binding.tvLoadingError.text = msg
binding.tvLoadingError.visibility = View.VISIBLE
binding.btnLoadingRetry.visibility = View.VISIBLE
}
}
}
顺便补一下 NoMoreException; 用法? 在下面 PagingSource 喽.
class NoMoreException: RuntimeException()
5.3 layout view_loading_more.xml
包含: TextView: 没有更多; ProgressBar: 加载中; TextView: 错误信息; Button: 重试按钮
5.4 PagingSource 需要根据情况 返回不同的 LoadResult
代码如下, 直接看注释就可以了;
class DynamicDataSource: PagingSource
private var maxPage = 1
override fun getRefreshKey(state: PagingState<Int, DynamicTwo>): Int? = null
override suspend fun load(params: LoadParams<Int>): LoadResult<Int, DynamicTwo> {
try {
val nextPageNumber = params.key ?: 1
//超过页码时, 返回没有更多状态 NoMoreException
if(nextPageNumber > maxPage){
return LoadResult.Error(NoMoreException())
}
//这是 Retrofit 网络请求
val map = mapOf("page" to nextPageNumber, "pageSize" to params.loadSize)
val param = ApiManager.INSTANCE.getJsonBody(map)
val response = ApiManager.INSTANCE.mApi.getDynamicList(param)
//后台 响应错误码时; 用 RuntimeException 返回错误信息
if(response.code != 200){
return LoadResult.Error(RuntimeException(response.msg))
}
//解析响应数据
val jo = response.data
val list = jo?.getAsJsonArray("newsList")?.toString()?.toBeanList<DynamicTwo>() ?: mutableListOf()
maxPage = jo?.get("totalPage").toString().toInt()
//返回正常数据
return LoadResult.Page(
data = list,
prevKey = null, // Only paging forward. 只向后加载就给null
// nextKey 下一页页码; 尾页给 null; 否则当前页码加1
nextKey = nextPageNumber + 1
)
} catch (e: IOException) {
// IOException for network failures.
return LoadResult.Error(e)
} catch (e: HttpException) {
// HttpException for any non-2xx HTTP status codes.
return LoadResult.Error(e)
} catch (e: Exception) {
// IOException for network failures.
return LoadResult.Error(e)
}
}
}
代码中 请求参数只给了 page 和 pageSize; 其他参数怎么给?
5.5 前台使用:
首先正常初始化 Adapter, RecycleView, 并调用 mViewModel?.flow?.collectLatest
其次 RecycleView 的 adaper 不要给 主数据Adapter; 而是给 withLoadStateFooter() 返回的 ConcatAdapter
val stateAdapter = mAdapter.withLoadStateFooter(MyLoadStateAdapter(mAdapter::retry))
mDataBind.rvRecycle.let {
it.layoutManager = LinearLayoutManager(mActivity)
// **** 这里不要给 mAdapter(主数据 Adapter); 而是给 stateAdapter ***
it.adapter = stateAdapter
}
PagingDataAdapter 的 withLoadStateFooter 方法会返回一个新的 ConcatAdapter 对象; 请将这个 ConcatAdapter 设置给 RecycleView
withLoadStateFooter 的参数 就是我们自定义的 MyLoadStateAdapter; retry -> mAdapter.retry()
5.6 看一下 LoadStateAdapter 的源码;
可以发现, 这是个单条目 Adapter.
并且 只有当 LoadState.Loading, LoadState.Error 时才会出现; 当然也可以重写 displayLoadStateAsItem(), 让它所有状态都出现;
当 列表状态变化时, 会设置 loadState 参数; 动态增删改 Item;
abstract class LoadStateAdapter
var loadState: LoadState = LoadState.NotLoading(endOfPaginationReached = false)
set(loadState) {
if (field != loadState) {
val oldItem = displayLoadStateAsItem(field)
val newItem = displayLoadStateAsItem(loadState)
if (oldItem && !newItem) {
notifyItemRemoved(0)
} else if (newItem && !oldItem) {
notifyItemInserted(0)
} else if (oldItem && newItem) {
notifyItemChanged(0)
}
field = loadState
}
}
final override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): VH {
return onCreateViewHolder(parent, loadState)
}
final override fun onBindViewHolder(holder: VH, position: Int) {
onBindViewHolder(holder, loadState)
}
final override fun getItemViewType(position: Int): Int = getStateViewType(loadState)
//条目数量, final 不可重写;
final override fun getItemCount(): Int = if (displayLoadStateAsItem(loadState)) 1 else 0
abstract fun onCreateViewHolder(parent: ViewGroup, loadState: LoadState): VH
abstract fun onBindViewHolder(holder: VH, loadState: LoadState)
open fun getStateViewType(loadState: LoadState): Int = 0
//只有当 Loading, Error 时, 才显示
open fun displayLoadStateAsItem(loadState: LoadState): Boolean {
return loadState is LoadState.Loading || loadState is LoadState.Error
}
}
5.7 LoadStateAdapter 改建头尾****
如果我们把它强行改造成 Header footer:
最终 Adapter:
class EndViewAdapter(val v: View) : LoadStateAdapter
override fun onCreateViewHolder(
parent: ViewGroup,
loadState: LoadState
) = EndHolder(v)
override fun onBindViewHolder(holder: EndHolder, loadState: LoadState){
//啥也不干
}
override fun displayLoadStateAsItem(loadState: LoadState) = true
}
class EndHolder(itemView: View) : RecyclerView.ViewHolder(itemView)
好吧, 一运行, 崩了 [捂脸]; called attach on a child which is not detached
怎么办, 取消 RecycleView 的刷新闪烁动画:
(mDataBind.rvRecycle.itemAnimator as SimpleItemAnimator).supportsChangeAnimations = false;
整个 RecycleView 的条目刷新动画都没了, 这不是个事啊! 但博主已经没办法了 [捂脸]
没办法了怎么办? 不用 Header 了? 当然不是, 我们只是不用 LoadStateAdapter 做头尾了; 我们用 ConcatAdapter 做头尾;
就是在 withLoadState… 之后, 再自己组装 ConcatAdapter
6. MAP: 数据转换; 有的时候, 我们需要对响应数据 进行预先处理;
例如: 根据条件,预先改变实体内容;
val flow: Flow
PagingConfig(pageSize = 10, prefetchDistance = 2,initialLoadSize = 10)
) {
DynamicDataSource()
}.flow
.cachedIn(viewModelScope)
.map {
it.map { entity ->
// 这里根据条件, 预先处理数据
if(entity.isLike == 1){
entity.nickName = "变变变, 我是百变小魔女"
}else{
entity.nickName = "呜哈哈哈"
}
entity
}
}
例如: 组合实体; 根据条件产生不同实体;
val flow: Flow
PagingConfig(pageSize = 10, prefetchDistance = 2,initialLoadSize = 10)
) {
DynamicDataSource()
}.flow
.cachedIn(viewModelScope)
.map {
it.map { entity ->
// 这里根据条件, 预先处理数据
if(entity.isLike == 1){
GroupEntity.DynamicTwoItem(entity)
}else{
GroupEntity.DynamicItem(DynamicEntity())
}
}
}
sealed class GroupEntity{
class DynamicTwoItem (val entity: DynamicTwo): GroupEntity()
class DynamicItem (val entity: DynamicEntity): GroupEntity()
}
又例如: 插入实体分隔符等
Over
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