我在组合Kotlin Flows和异步DiffUtil时遇到麻烦。
我在RecyclerView.Adapter中具有此功能,该功能在计算线程上计算DiffUtil并将更新分发到Main线程上的RecyclerView中:
suspend fun updateDataset(newDataset: List<Item>) = withContext(Dispatchers.Default) {
val diff = DiffUtil.calculateDiff(object : DiffUtil.Callback()
{
override fun areItemsTheSame(oldItemPosition: Int, newItemPosition: Int): Boolean
= dataset[oldItemPosition].conversation.id == newDataset[newItemPosition].conversation.id
override fun getOldListSize(): Int = dataset.size
override fun getNewListSize(): Int = newDataset.size
override fun areContentsTheSame(oldItemPosition: Int, newItemPosition: Int): Boolean
= dataset[oldItemPosition] == newDataset[newItemPosition]
})
withContext(Dispatchers.Main) {
dataset = newDataset // <-- dataset is the Adapter's dataset
diff.dispatchUpdatesTo(this@ConversationsAdapter)
}
}
我从Fragment中这样调用此函数:
private fun updateConversationsList(conversations: List<ConversationsAdapter.Item>)
{
viewLifecycleOwner.lifecycleScope.launch {
(listConversations.adapter as ConversationsAdapter).updateDataset(conversations)
}
}
在很短的时间内多次调用
updateConversationsList()
,因为此功能由Kotlin的Flows
调用,例如Flow<Conversation>
。现在,尽管如此,有时我还是遇到了
java.lang.IndexOutOfBoundsException: Inconsistency detected. Invalid view holder adapter positionViewHolder
错误。阅读this thread我了解这是一个线程问题,并且我阅读了很多类似this one的建议,这些建议都说:更新适配器数据集的线程和将更新分发给RecyclerView的线程必须相同。如您所见,我已经做到了:
withContext(Dispatchers.Main) {
dataset = newDataset
diff.dispatchUpdatesTo(this@ConversationsAdapter)
}
由于主线程(只有它)执行这两个操作,所以我怎么可能出现此错误?
最佳答案
你的差异在比赛。如果您的更新在短期内出现两次,则可能会发生:
Adapter has dataset 1 @Main
Dataset 2 comes
calculateDiff between 1 & 2 @Async
Dataset 3 comes
calculateDiff between 1 & 3 @Async
finished calculating diff between 1 & 2 @ Async
finished calculating diff between 1 & 3 @ Async
Dispatcher main starts handling messages
replace dataset 1 with dataset 2 using 1-2 diff @Main
replace dataset 2 with dataset 3 using 1-3 diff @Main - inconsistency
替代方案是1-3之间的差异可以在1-2之前完成,但问题仍然相同。
您必须在出现新计算时取消正在进行的计算,并防止部署无效的差异,例如,在片段中存储作业参考:
var updateJob : Job? = null
private fun updateConversationsList(conversations: List<ConversationsAdapter.Item>)
{
updateJob?.cancel()
updateJob = viewLifecycleOwner.lifecycleScope.launch {
(listConversations.adapter as ConversationsAdapter).updateDataset(conversations)
}
}
如果您取消它,则
withContext(Dispatchers.Main)
将在内部检查延续状态,并且不会运行。