在FirebaseUI的FirebaseRecyclerAdapter

Question

我写了一个基于FirebaseUI documentation的自定义FirebaseRecylerAdapter，如下所示：

class FavoritesAdapter(lifecycleOwner: LifecycleOwner) : FirebaseRecyclerAdapter<Favorite, FavoritesAdapter.FavoritesHolder>(buildOptions(lifecycleOwner)) {

companion object {
    private fun buildQuery() = FirebaseDatabase.getInstance()
            .reference
            .child("favorites")
            .limitToLast(50)

    private fun buildOptions(lifecycleOwner: LifecycleOwner) = FirebaseRecyclerOptions.Builder<Favorite>()
            .setQuery(buildQuery(), Favorite::class.java)
            .setLifecycleOwner(lifecycleOwner)
            .build()
}

//...

该类重写onDataChanged（）函数：

override fun onDataChanged() {
    // Called each time there is a new data snapshot. You may want to use this method
    // to hide a loading spinner or check for the "no documents" state and update your UI.
    // ...

}

现在，我如何实际检查“无文档”状态以更新我的UI？我找不到检查空数据集的方法。我正在寻找类似getItemCount（）的东西。

Answer 1

适配器确实具有itemCount属性，您还可以使用snapshots获取模型对象的实时列表。例如：

override fun onDataChanged() {
    if (itemCount == 0) {
        // Do stuff
    }
}