Android Paging 3 在 invalidate() 上清除 recyclerview

Question

我有一个可以应用过滤器的分页列表。用户应用过滤器后，recyclerview 应该在加载页脚中显示 0 个项目，直到它加载第一个项目并触发 LoadResul.Error 以防没有可显示的内容。

页脚工作正常，但您仍然可以看到调用 .invalidate() 之前存在的数据，并且您会看到该数据，直到它从后端获得新的响应（如果您的网络不好，这可能需要一些时间） .并且如果出现错误，旧项目仍然存在，并且会出现错误页脚。

关于如何实现这一点的任何想法？

我也在使用带有 RxJava 的库，所以这里是 DataSource 代码：

    override fun getRefreshKey(state: PagingState<Int, Event>): Int = 1

    override fun loadSingle(params: LoadParams<Int>): Single<LoadResult<Int, Event>> {
        val key = params.key ?: 1

        return repository.getCityEvents(
            cityId = globalData.currentCityId,
            start = selectedDates?.start?.toApiFormat(),
            end = selectedDates?.end?.toApiFormat(),
            pageNo = key,
            categories = categoryFilters
        )
            .map { it.content }
            .map { toLoadResult(it, params) }
            .onErrorReturn { LoadResult.Error(it) }
    }

    private fun toLoadResult(data: List<Event>, params: LoadParams<Int>): LoadResult<Int, Event> {
        val currentKey = params.key ?: 1

        return if (data.isEmpty() && currentKey == 1)
            LoadResult.Error(NoEventsException())
        else
            LoadResult.Page(
                data = data,
                prevKey = null,
                nextKey = if (data.size < params.loadSize) null else currentKey + 1
            )
    }

Answer 1

首先，您需要将LoadStateAdapter 添加到您的PagingDataAdapter，如下所示：

item_paging_loading.xml:

<?xml version="1.0" encoding="utf-8"?>
<androidx.appcompat.widget.LinearLayoutCompat xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical"
    android:padding="12dp">

    <ProgressBar
        android:id="@+id/progressbar"
        android:layout_width="32dp"
        android:layout_height="32dp"
        android:layout_gravity="center_horizontal" />

    <TextView
        android:id="@+id/textError"
        style="@style/TextSmall"
        android:layout_gravity="center"
        android:gravity="center"
        android:visibility="gone"
        tools:text="Some Error Occurred"
        tools:visibility="visible" />

    <TextView
        android:id="@+id/buttonRetry"
        style="@style/TextMedium"
        android:layout_gravity="center"
        android:background="?selectableItemBackground"
        android:padding="@dimen/_5dp"
        android:text="@string/retry"
        android:textColor="@color/colorAccent" />
</androidx.appcompat.widget.LinearLayoutCompat>

PaginationLoadStateAdapter.kt

class PaginationLoadStateAdapter(
    val retry: () -> Unit
) : LoadStateAdapter<PaginationLoadStateAdapter.PassengersLoadStateViewHolder>() {

    inner class PassengersLoadStateViewHolder(
        private val binding: ItemPagingLoadingBinding,
        private val retry: () -> Unit
    ) : RecyclerView.ViewHolder(binding.root) {
        fun bind(loadState: LoadState) {
            if (loadState is LoadState.Error) {
                binding.textError.text = loadState.error.localizedMessage
            }
            binding.progressbar.visible(loadState is LoadState.Loading)
            binding.buttonRetry.visible(loadState is LoadState.Error)
            binding.textError.visible(loadState is LoadState.Error)
            binding.buttonRetry.setOnClickListener {
                retry()
            }
        }
    }

    override fun onBindViewHolder(
        holder: PassengersLoadStateViewHolder,
        loadState: LoadState
    ) {
        holder.bind(loadState)
    }

    override fun onCreateViewHolder(
        parent: ViewGroup,
        loadState: LoadState
    ) = PassengersLoadStateViewHolder(
        ItemPagingLoadingBinding.inflate(
            LayoutInflater.from(parent.context), parent, false
        ),
        retry
    )
}

为PagingDataAdapter添加页眉和页脚的扩展功能

fun <T : Any, V : RecyclerView.ViewHolder> PagingDataAdapter<T, V>.withLoadStateAdapters(
    header: LoadStateAdapter<*>,
    footer: LoadStateAdapter<*>
): ConcatAdapter {
    addLoadStateListener { loadStates ->
        header.loadState = loadStates.refresh
        footer.loadState = loadStates.append
    }

    return ConcatAdapter(header, this, footer)
}

你需要像这样为你的 RV 设置页眉和页脚：

binding.list.adapter = pagingDataAdapter.withLoadStateAdapters(
                header = PaginationLoadStateAdapter { adapterSimpleOffers.retry() },
                footer = PaginationLoadStateAdapter { adapterSimpleOffers.retry() }
            )

用户应用过滤器后，您可以提交空数据以显示 0 个项目，然后再次加载您的分页。

pagingDataAdapter.submitData(lifecycle, PagingData.empty())
loadData()//load your data