Android 第 3 页未加载下一页

Question

从自定义分页实施迁移到 Jetpack Paging 3 库后，数据未按预期加载。 首页根据Pager的PagingConfig正确处理:

internal fun createProductListPager(pagingSource: ProductListPagingSource): Pager<Int, Product> = Pager(
    config = PagingConfig(
        pageSize = 10,
        prefetchDistance = 2,
    ),
    initialKey = 0,
) { pagingSource }

这是 Adapter 的摘录：

public class PagingProductCardAdapter(private val viewBinder: CoreViewBinder) :
    PagingDataAdapter<Listable, RecyclerView.ViewHolder>(viewBinder.getDiffUtils()) {


    public val list: List<Listable>
        get() = snapshot().items


    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder {
      // ...
    }

    override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
        viewBinder.bind(list[position], holder)
    }
    // ...
}

当滚动到 RecyclerView 底部时，下一页根本没有加载（没有调用PagingSource.load()）会出什么问题？

Answer 1

PagingSource 如何知道何时加载更多数据？它背后有什么魔力？
好吧，结果是 适配器负责这个 。 Adapter 如何知道加载的数据？您必须按照记录调用 getItem()：

/**
 * Returns the presented item at the specified position, notifying Paging of the item access to
 * trigger any loads necessary to fulfill [prefetchDistance][PagingConfig.prefetchDistance].
 *
 * @param position Index of the presented item to return, including placeholders.
 * @return The presented item at [position], `null` if it is a placeholder
 */
protected fun getItem(@IntRange(from = 0) position: Int) = differ.getItem(position)

当我们通过快照访问整个列表时：

public val list: List<Listable>
    get() = snapshot().items

适配器不知道正在加载什么项目，也无法触发下一页加载。

所以修复是：

override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
    getItem(position)?.let {
        viewBinder.bind(list[position], holder)
    }
}

有了这个，一切正常！

Android 第 3 页未加载下一页

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