目前体验下来感觉只是帮我们做了当前页面page的自增，更多的使用方法待补充。
Model
https://jsonplaceholder.typicode.com/，是一个提供假json数据接口的网站，给前端开发者来做Demo最合适不过，这里我拿其中的相册列表接口来做一个相册列表页面。
data class AlbumModel(
val albumId: Int,
val id: Int,
val title: String,
val url: String,
val thumbnailUrl: String
)
interface AlbumDataApi {
@GET(“albums/{page}/photos”)
suspend fun getAlbumByPage(@Path(“page”) page: Int, @Query(“pageSize”) pageSize: Int): List
}
ViewModel
在ViewModel中需要我们去构造一个Pager对象，设置一些分页参数，初始化Item数量，每页的Item数量，预加载大小，最大item数量等。
然后通过Pager中方法可以拿到Flow或者LiveData，我这里选择了使用Flow
class AlbumViewModel : ViewModel() {
private val client = APIClient
private val pager = Pager(
config = PagingConfig(
initialLoadSize = AlbumPagingSource.PAGE_SIZE,
pageSize = AlbumPagingSource.PAGE_SIZE,
prefetchDistance = AlbumPagingSource.PAGE_SIZE,
enablePlaceholders = false
),
pagingSourceFactory = { AlbumPagingSource(client) }
)
//返回Album数据流
fun getHomeDataFlow(): Flow<PagingData<AlbumModel>> {
return pager.flow
}
}
RecycleView 适配器
继承PagingDataAdatper，构造参数需要一个DiffUtil，方法中用相册的Id来判断是不是同一个相册Item
同样需要重写onBindViewHolder、onCreateViewHolder方法和新建类AlbumViewHolder类继承ViewHolder
不过父类中提供了getItem(position: Int)方法来直接获取AlbumModel，解决了之前需要我们自己从数组里取的繁琐。
class AlbumAdapter :
PagingDataAdapter<AlbumModel, AlbumAdapter.AlbumViewHolder>(DiffCallback) {
companion object {
private val DiffCallback = object : DiffUtil.ItemCallback<AlbumModel>() {
override fun areItemsTheSame(oldItem: AlbumModel, newItem: AlbumModel): Boolean {
return oldItem.id == newItem.id
}
override fun areContentsTheSame(oldItem: AlbumModel, newItem: AlbumModel): Boolean {
return oldItem.id == newItem.id
}
}
}
override fun onBindViewHolder(holder: AlbumViewHolder, position: Int) {
val albumModel = getItem(position)
albumModel?.let {
holder.tvAlbumTitle.text = albumModel.title
Glide.with(holder.itemView.context)
.load(albumModel.url)
.into(holder.ivAlbumImage)
}
}
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): AlbumViewHolder {
...
}
class AlbumViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
...
}
}
class AlbumPagingSource(private val client: APIClient) : PagingSource<Int, AlbumModel>() {
companion object {
const val PAGE_SIZE = 10
}
override suspend fun load(params: LoadParams<Int>): LoadResult<Int, AlbumModel> {
return try {
val currentPage = params.key ?: 1
val pageSize = params.loadSize
val AlbumModels = client.getHomeData(currentPage, pageSize)
val preKey = if (currentPage > 1) currentPage - 1 else null
val nextKey = if (AlbumModels.isNotEmpty()) currentPage + 1 else null
LoadResult.Page(AlbumModels, preKey, nextKey)
} catch (e: Exception) {
LoadResult.Error(throwable = e)
}
}
override fun getRefreshKey(state: PagingState<Int, AlbumModel>): Int? {
return state.anchorPosition?.let { anchorPosition ->
state.closestPageToPosition(anchorPosition)?.prevKey?.plus(1)
?: state.closestPageToPosition(anchorPosition)?.nextKey?.minus(1)
}
}
}
Fragment
最后我们在Fragment中收集ViewModel中的AlbumData Flow，通过adapter的submitData方法通知PagingDataAdpater来刷新数据。
override fun onCreateView(...): View {
...
//给RecycleView设置Adapter和LayoutManager
binding.rvAlbum.layoutManager = GridLayoutManager(activity, 2)
binding.rvAlbum.adapter = adapter
//收集相册数据
lifecycleScope.launch {
homeViewModel.getHomeDataFlow().collect {
adapter.submitData(it)
}
}
return binding.root
}