android - 具有Room的PagedListAdapter和ItemTouchHelper-如何在onMove()期间更新

我遇到的问题是，在我的RecyclerView上拖动一个项时，onMove()回调无法更改项数组的实际顺序，因为该数组由PagedListAdapter管理。如果我在数据库上执行，这会在后台线程上发生，因为Room需要我执行此操作（无论如何，我确实应该在后台线程上执行数据库），正如您所想象的，在拖动项时，这不太好。
我对ItemTouchHelper如何工作的理解是，在onMove()上，我必须重新排列任何我想可视化显示的内容，然后才能在clearView()上保存到数据库。但我不能在onMove()上重新排列。
这是我当前代码的一个简化，它可以工作，但是拖动的视觉提示不能很好地工作。

inner class SwipeCallback() : ItemTouchHelper.SimpleCallback(ItemTouchHelper.UP or ItemTouchHelper.DOWN, ItemTouchHelper.RIGHT) {
        override fun onMove(recyclerView: RecyclerView, viewHolder: RecyclerView.ViewHolder, target: RecyclerView.ViewHolder): Boolean {
            val item1 = getItem(viewHolder.adapterPosition)
            val item2 = getItem(target.adapterPosition)
            if (item1 != null && item2 != null) {
                //BASICALLY JUST SWAPPING THE TWO POSITIONS ON THE OBJECTS but not doing anything with the adapter array because the PagedListAdapter doesn't allow me to modify the array as far I know.
                swapItems(item1,item2)

                }
                return true
            }
            return false
        }

        override fun onSwiped(viewHolder: RecyclerView.ViewHolder, direction: Int) {
            TODO("not implemented") //To change body of created functions use File | Settings | File Templates.
        }

        override fun isLongPressDragEnabled(): Boolean {
            return false
        }

        override fun onSelectedChanged(viewHolder: RecyclerView.ViewHolder?, actionState: Int) {
            super.onSelectedChanged(viewHolder, actionState)
            if (actionState == ACTION_STATE_DRAG) {
                viewHolder?.itemView?.alpha = 0.5f
            }
        }

        override fun clearView(recyclerView: RecyclerView,
                               viewHolder: RecyclerView.ViewHolder) {
            super.clearView(recyclerView, viewHolder)

            viewHolder?.itemView?.alpha = 1.0f

            //THIS IS WHERE I UPDATED THE DB, currentList is the PagedListAdapter array. This is an inner class of my PagedListAdapter.
            currentList?.let {updateList(it) }
        }
    }

那么，我怎样才能使这个工作视觉化呢？
谢谢。

最佳答案

更新：I created an example here
我假设您正在使用room数据库将分页数据加载到ui。事实上，如果使用分页库，这是使列表能够响应数据动态变化的唯一方法。
在适配器中，只需通知数据库在onmove（）函数中进行更改

    class SwipeCallback(
        private val adapter: HomeSpotAdapter,
        private val onItemMove: (from: Int, to: Int) -> Unit
    ) : ItemTouchHelper.SimpleCallback(ItemTouchHelper.UP or ItemTouchHelper.DOWN, ItemTouchHelper.RIGHT) {

        override fun onMove(
            recyclerView: RecyclerView,
            viewHolder: RecyclerView.ViewHolder,
            target: RecyclerView.ViewHolder
        ): Boolean {
            val from = viewHolder.adapterPosition
            val to = target.adapterPosition
            val item1 = adapter.getItem(from)
            val item2 = adapter.getItem(to)
            if (item1 != null && item2 != null) {

                // Notify database to swap items here
                onItemMove(from, to)

                return true
            }
            return false
        }

        override fun onSwiped(viewHolder: RecyclerView.ViewHolder, direction: Int) {
        }

        override fun isLongPressDragEnabled(): Boolean {

            // It has to be true
            return true
        }

        override fun onSelectedChanged(viewHolder: RecyclerView.ViewHolder?, actionState: Int) {
            super.onSelectedChanged(viewHolder, actionState)
            if (actionState == ACTION_STATE_DRAG) {
                viewHolder?.itemView?.alpha = 0.5f
            }
        }

        override fun clearView(recyclerView: RecyclerView,
                               viewHolder: RecyclerView.ViewHolder) {
            super.clearView(recyclerView, viewHolder)
            viewHolder.itemView.alpha = 1.0f

            // Don't need to do anything here
        }
    }

在fragment中，我们将onimmove lambda函数传递给适配器

        ItemTouchHelper(HomeSpotAdapter.SwipeCallback(adapter) { from, to ->
            viewModel.swapItems(from, to)
        }).apply {
            attachToRecyclerView(recyclerView.getRecycler())
        }

要交换数据库中的项，基本上我们可以使用这样的swap items（）函数

    fun swapItem(from: Int, to: Int) {

        // I'm using executor to run query in worker thread here, but you can choose whatever you want

        Executors.newSingleThreadExecutor().execute {

            val item1 = db.HomeSpotDao().getSpot(from)
            val item2 = db.HomeSpotDao().getSpot(to)

            // Swap index of 2 items

            val newItem1 = item1.copy()
            newItem1.indexInResponse = item2.indexInResponse

            val newItem2 = item2.copy()
            newItem2.indexInResponse = item1.indexInResponse

            db.HomeSpotDao().updateSpot(newItem1)
            db.HomeSpotDao().updateSpot(newItem2)
        }
    }

您可以在google示例中查看这个类，以了解如何使用indexinresponse来跟踪列表中项目的索引
Link google sample here