Android Paging3 LoadStateAdapter显示已加载完所有数据

问题描述：

使用paging3的过程中，本想通过为PagingDataAdaper添加页脚LoadStateAdapter方法onBindViewHolder(holder: LoadStateViewHolder, loadState: LoadState)中的loadState显示loading、error、no more,但是处理no more的时候发现loadState.endOfPaginationReached一直是false，且loadState只有LoadState.Loading、LoadState.Error两种状态

查看源码：

PagingDataAdapter.kt

fun withLoadStateFooter(
    footer: LoadStateAdapter<*>
): MergeAdapter {
    addLoadStateListener { loadStates ->
        footer.loadState = loadStates.append
    }
    return MergeAdapter(this, footer)
}

LoadStateAdapter.kt

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
        }
    }

/**
 * Returns true if the LoadState should be displayed as a list item when active.
 *
 * By default, [LoadState.Loading] and [LoadState.Error] present as list items, others do not.
 */
open fun displayLoadStateAsItem(loadState: LoadState): Boolean {
    return loadState is LoadState.Loading || loadState is LoadState.Error
}

通过查看源码可知，只有newItem为true才显示布局UI，若要newItem为true，则loadState的状态只有LoadState.Loading、LoadState.Error，故LoadStateAdapter只有loading、error两个状态。

解决方案：

监听PagingDataAdapter.addLoadStateListener可知，列表加载到底部会触发loadState.append的NotLoading(endOfPaginationReached=true)状态。

以上，想要通过loadState.endOfPaginationReached属性判断是否到底部，只有拿到loadState的NotLoading状态，通过重写displayLoadStateAsItem方法返回true即可。

    override fun displayLoadStateAsItem(loadState: LoadState): Boolean {
        return true
    //    return loadState is LoadState.Loading || loadState is LoadState.Error || loadState is LoadState.NotLoading
    }

上面两种返回值效果一样，loadState的loading、error、notLoading三种状态都会触发。