Android Paging库不会触发loadAfter() [英] Android Paging library doesn't fire loadAfter()

问题描述

我正在使用新的Android Paging库获取具有无限滚动的RecyclerView.我不明白为什么当我这样设置PagedList时，库不触发loadAfter()方法:

I'm using the new Android Paging library to get a RecyclerView with infinite scrolling. I cannot understand why the library does not fire the loadAfter() method when I setup my PagedList like this:

val config: PagedList.Config = PagedList.Config.Builder()
                .setEnablePlaceholders(false)
                .setPageSize(10)
                .setPrefetchDistance(1)
                .setInitialLoadSizeHint(10)
                .build()
val pageList = PagedList.Builder(LookDataSource(lookList), config)
                .setInitialKey(0)
                .setMainThreadExecutor(MainThreadExecutor())
                .setBackgroundThreadExecutor(PaginationThreadPoolExecutor())
                .setBoundaryCallback(LookBoundaryCallback())
                .build()

注意:我的prefetchDistance为1，因为我想在看到最后一个项目时加载另一批数据.文档说0表示永远不会加载更多数据

Note: my prefetchDistance is 1, since I want to load another batch of data when my last item is seen. The documentation says that 0 would be to never load more data

我的数据源是 PageKeyedDataSource ，键是页面的索引.

My DataSource is a PageKeyedDataSource, and the key is the index of the page.

我研究了 ContiguousPagedList 的源代码，这是您使用PageKeyedDataSource时创建的特定PagedList，但我听不懂这些内容:

I have looked into the source code of ContiguousPagedList which is the particular PagedList created when you use a PageKeyedDataSource and I cannot understand these :

@MainThread
@Override
protected void loadAroundInternal(int index) {
    int prependItems = mConfig.prefetchDistance - (index - mStorage.getLeadingNullCount());
    int appendItems = index + mConfig.prefetchDistance
            - (mStorage.getLeadingNullCount() + mStorage.getStorageCount());

    mPrependItemsRequested = Math.max(prependItems, mPrependItemsRequested);
    if (mPrependItemsRequested > 0) {
        schedulePrepend();
    }

    mAppendItemsRequested = Math.max(appendItems, mAppendItemsRequested);
    if (mAppendItemsRequested > 0) {
        scheduleAppend();
    }
}

根据我的配置，当我看到最后一个项目时， appendItems 值为0

According to my configuration, the appendItems value is 0 when my last item is seen

int appendItems =索引+ mConfig.prefetchDistance -(mStorage.getLeadingNullCount()+ mStorage.getStorageCount());

int appendItems = index + mConfig.prefetchDistance - (mStorage.getLeadingNullCount() + mStorage.getStorageCount());

与

• 索引+ 9(页面大小为10的最后一项)
• prefetchDistance为1
• leadingNullCount始终为0(不确定我是否了解此属性)
• storageCount是我在上面配置的pageSize(根据此类的源代码)

给予

int appendItems = 9 + 1(0-10)

int appendItems = 9 + 1 (0 - 10)

基于此， scheduleAppend()不会被调用，因为 mAppendItemsRequested 始终也为0.

Based on this, the scheduleAppend() is never called since mAppendItemsRequested is always 0 too.

我发现在滚动上实际加载更多数据的唯一方法是将我的prefetchDistance设置为大于1的任何值.话虽如此，它似乎比解决此问题的方法要好得多.

The only way I found to actually load more data on scroll is to set my prefetchDistance to any value superior to 1. That being said, it seems more like a workaround than the good answer to this problem.

推荐答案

用PagedListAdapter替换ListAdapter

Replace ListAdapter with PagedListAdapter

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