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Android Leanback: How to update nested rows item in RowsSupportFragment

Hey Guys
I'm working on androidTV application using leanback library.
I should show list of categories that each category has it's own list of contents. For this approach leanback offered RowsSupportFragment that you can show this type of UI inside that.
Here I am using Room + LiveData + Retrofit + Glide to perform and implement the screen, but the issue is here, the api will not pass content cover images directly, so developer should download each content cover image, store it and then show covert over the content.
Every thing is working but at the first time, If there is no cover image for content, I will download the cover and store it, but content will not be triggered to get and show image. Using notifyItemRangeChanged and methods like this will blink and reset the list row so this is not a good solution.
This is my diffUtils that I'm using, one for category list, one for each contents list.
private val diffCallback = object : DiffCallback<CardListRow>() {
override fun areItemsTheSame(oldItem: CardListRow, newItem: CardListRow): Boolean {
return oldItem.id == newItem.id
}
override fun areContentsTheSame(oldItem: CardListRow, newItem: CardListRow): Boolean {
return oldItem.cardRow.contents?.size == newItem.cardRow.contents?.size
}
}
private val contentDiffCallback = object : DiffCallback<ContentModel>() {
override fun areItemsTheSame(oldItem: ContentModel, newItem: ContentModel): Boolean {
return oldItem.id == newItem.id
}
override fun areContentsTheSame(oldItem: ContentModel, newItem: ContentModel): Boolean {
return oldItem.hashCode() == newItem.hashCode()
}
}
As I said, for storage I'm using room, retrieving data as LiveData and observing them in my fragment and so on. I have not posted all the codes for summarization.
If you have any idea or similar source code, I would appreciate it. Thanks
Edit: Fri Dec 2 --- add some more details
This is my live-data observer that holds and observe main list on categories and datas
private fun initViewModel() {
categoriesViewModel.getCategoriesWithContent().observe(viewLifecycleOwner) { result ->
val categoryModelList = MergedContentMapper().toCategoryModelList(result)
initData(categoryModelList)
}
}
And this is the row creation scenario using ArrayObjectAdapter
private fun initData(categoryModelList: List<CategoryModel>) {
showLoading(false)
createRows(categoryModelList)
}
private fun createRows(categoryModelList: List<CategoryModel>) {
val rowItemsList: MutableList<CardListRow> = arrayListOf()
// create adapter for the whole fragment. It displays Rows.
categoryModelList.forEach { categoryModel ->
// create adapter for each row that can display CardView using CardPresenter
val cardListRow = createCardRow(categoryModel)
// add card list rows into list
rowItemsList.add(cardListRow)
}
// set item with diff util
rowsAdapter.setItems(rowItemsList, diffCallback)
}
private fun createCardRow(categoryModel: CategoryModel): CardListRow {
val contentList = categoryModel.contents ?: emptyList()
val cardListRowsAdapter = ArrayObjectAdapter(CardPresenterSelector(context, this))
cardListRowsAdapter.setItems(contentList, contentDiffCallback)
val headerItem = HeaderItem(categoryModel.title)
return CardListRow(headerItem, cardListRowsAdapter, categoryModel)
}

Your code looks correct, but it's missing the part where you tell the Presenter what changed on your items so it can change only that piece of data and doesn't need to re-bind the entire content avoiding the blink.
After your DiffCallback detects that the items are the same but the content has changed it will call its getChangePayload() function to gather details about the changes to pass them to the Presenter. To achieve that you need to do the following changes:
First, you need to override the DiffCallback.getChangePayload() function to something like this:
override fun getChangePayload(oldItem: ListRow, newItem: ListRow): Any {
return when {
oldItem.headerItem.name != newItem.headerItem.name -> "change_title"
else -> "change_items"
}
}
With that your ListRowPresenter will receive the information of what changed in the ListRowPresenter.onBindViewHolder() overload that receives a payload list (returned by your DiffCallback) like so:
override fun onBindViewHolder(
viewHolder: Presenter.ViewHolder?,
item: Any?,
payloads: MutableList<Any>?
) {
when {
payloads == null || payloads.isEmpty() -> {
// Your DiffCallback did not returned any information about what changed.
super.onBindViewHolder(viewHolder, item, payloads)
}
"change_title" in payloads -> getRowViewHolder(viewHolder)?.let {
headerPresenter.onBindViewHolder(it.headerViewHolder, item)
}
"change_items" in payloads -> {
val newItems = ((item as? ListRow)?.adapter as? ArrayObjectAdapter)?.unmodifiableList<Item>()
when (val listRowAdapter = (getRowViewHolder(viewHolder).row as? ListRow)?.adapter) {
is ArrayObjectAdapter -> listRowAdapter.setItems(newItems, null)
else -> super.onBindViewHolder(viewHolder, item, payloads)
}
}
else -> {
// If you don't know what changed just delegate to the super.
super.onBindViewHolder(viewHolder, item, payloads)
}
}
}
Customize the implementation of DiffCallback.getChangePayload() to your needs. You can return a list of changes in this function and treat all of them in your ListRowPresenter.onBindViewHolder().
I recently wrote a blog post with samples that might help.

Kotlin ListAdapter reset RecyclerView after submitList

I'm working on android apps using MVVM, and Data Binding. I'm using ListAdapter for my RecyclerView Adapter. The case is, when I submit new data to the adapter using submitList, it reset RecyclerView scroll position. It blink at first and just reset it's position to the top.
My Binding Adapter
#BindingAdapter("listTemplate", "hirarki")
fun bindListTemplate(recyclerView: RecyclerView, data: List<Template>?, hirarki: Int) {
var adapter = recyclerView.adapter as TemplateChiefAdapter
adapter.submitList(data)
}
TemplateFragment where I resubmit my data
navController.currentBackStackEntry?.savedStateHandle?.getLiveData<Boolean>("shouldUpdate")
?.observe(viewLifecycleOwner, {
if (it) {
viewModel.fetchdata()
navController.currentBackStackEntry?.savedStateHandle?.remove<Boolean>("shouldUpdate")
}
})
This piece of code will update LiveData in my ViewModel, so the DataBinding will detect its change and re-submitList the data to the adapter
My List Adapter
class TemplateChiefAdapter(val onClickListener: OnClickListener) : ListAdapter<Template, TemplateChiefAdapter.TemplateChiefViewHolder>(DiffCallback) {
class TemplateChiefViewHolder(private var binding: ItemTemplateChiefBinding) : RecyclerView.ViewHolder(binding.root) {
fun bind(template: Template) {
binding.template = template
binding.executePendingBindings()
}
}
companion object DiffCallback : DiffUtil.ItemCallback<Template>() {
override fun areItemsTheSame(oldItem: Template, newItem: Template): Boolean {
return oldItem === newItem
}
override fun areContentsTheSame(oldItem: Template, newItem: Template): Boolean {
return oldItem.id_template == newItem.id_template
}
}
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): TemplateChiefViewHolder {
return TemplateChiefViewHolder(ItemTemplateChiefBinding.inflate(LayoutInflater.from(parent.context)))
}
override fun onBindViewHolder(holder: TemplateChiefViewHolder, position: Int) {
val template = getItem(position)
holder.itemView.setOnClickListener {
onClickListener.onClick(template)
}
holder.bind(template)
}
class OnClickListener(val listener: (template: Template) -> Unit) {
fun onClick(template: Template) = listener(template)
}
}
How can I keep the recycler scroll position after submitList called?

I didn't examine in ultra detail all your code, but the DiffUtil Callback caught my attention.
areItemsTheSame is an optimization from the DiffUtil class to determine if the items changed position. If the didn't, then the contents can be checked, and re-bound to their new data if it changed. If the positions changed, then the item may need to be animated elsewhere or well.. as you can imagine it becomes more complicated from there.
The idea of that method is to compare if the items are the same or not, not to compare the entire item. I would use an id (or anything that can help you identify uniqueness in your items). You are using the === operator and I don't know the rest of your architecture, but comparing by reference may not be accurate if, for instance, your data layer transforms and copies these objects around (something you can't/shouldn't tell/care for in your adapter).
For instance, instead of
return oldItem === newItem
You could do
return oldItem.someId === newItem.someId
This would ensure that even if your items are the same but were copied/recreated/etc., you'd still identify them as such despite them being a different reference.
Then, in areContentsTheSame you are expected to check all the contents that you consider instrumental in deciding if onBind must be called on your specific viewHolder because the contents are different. So I would have expected something more like:
oldItem.something == newItem.something
&& oldItem.xxx == newItem.xxx
&& oldItem.yyy == newItem.yyy
(but maybe with DataBinding you don't need this, I wouldn't know).
All that being said, I have 0.1 experience with DataBinding (and personally for me that was enough), so if this is related in anyway how the data binding library behaves, I can't help you any more. :/
From a RecyclerView's point of view, the rest of the code looks adequate.

Delete Item in Android ViewPager2

I am updating my code from using androidx.viewpager to androidx.viewpager2. I am paging through an undetermined number of fragments showing data records retrieved from a database. Loading the view pager and paging through my data works nicely but I'm having some trouble with deleting an item and updating the pager adapter. I want to delete an item at any given position by calling the removeItem() method (see code below) on my adapter. That should remove the item from my database as well as my fragment and then update the view.
Result is that the correct item is removed from the database. But it does not remove the intended fragment from my view pager but the next page instead. The current page remains visible. I have a bit offsetting the position by plus or minus 1 with no success - in contrary: in those cases my delete routine performed as initially expected. I also tried similar considerations as given e.g. here.
I'd like to achieve the following behavior:
When deleting any item, the page should be removed and the next one in the list displayed.
When deleting the last/rightmost item in the list, the page should be removed and the previous (now last) page shown.
When deleting the last remaining item (none left) the activity should finish.
My adapter code:
internal class ShapePagerAdapter(private val activity: AppCompatActivity) : FragmentStateAdapter(activity) {
private val dbManager: DatabaseManager
private var shapeIds: MutableList<String>? = null
init {
dbManager = DatabaseManager(activity)
try {
shapeIds = dbManager.getShapeIds()
} catch (e: DatabaseAccessException) {
// ...
}
}
override fun getItemCount(): Int {
return if (null != shapeIds) shapeIds!!.size else 0
}
override fun createFragment(position: Int): Fragment {
return ShapeFragment.newInstance(shapeIds!![position])
}
fun removeItem(activity: AppCompatActivity, position: Int) {
try {
// Remove from Database.
dbManager.deleteShape(shapeIds!![position])
// Remove from View Pager.
shapeIds!!.removeAt(position)
notifyItemRemoved(position)
notifyItemRangeChanged(position , itemCount)
// Close if nothing to show anymore.
if (itemCount == 0) {
activity.finish()
}
} catch (e: DatabaseAccessException) {
// ...
}
}
}

Closer study of FragmentStateAdapter reveals that two of its methods must be overridden in this case:
containsItem(long itemId) and getItemId(int position)
Default implementation works for collections that don't add, move,
remove items.
Searching for that I found an answer to a similar question, pointing me in the right direction. It does not produce the exact behavior given in my question, which is why I'm posting a slightly adapted version.
Key is that those two methods are implemented in cases there can be changes to the sequence of items. To enable this I maintain a map of items and item ids and update when there are changes to the sequence, in this case a removed item.
internal class ShapePagerAdapter(private val activity: AppCompatActivity) : FragmentStateAdapter(activity) {
private val dbManager: DatabaseManager
private lateinit var shapeIds: MutableList<String>
private lateinit var itemIds: List<Long>
init {
dbManager = DatabaseManager(activity)
try {
shapeIds = dbManager.getShapeIds()
updateItemIds()
} catch (e: DatabaseAccessException) {
// ...
}
}
override fun getItemCount(): Int = shapeIds.size
override fun createFragment(position: Int): Fragment = ShapeFragment.newInstance(shapeIds[position])
fun removeItem(activity: AppCompatActivity, position: Int) {
try {
dbManager.deleteShape(shapeIds[position])
shapeIds.removeAt(position)
notifyItemRemoved(position)
notifyItemRangeChanged(position , itemCount)
updateItemIds()
if (itemCount == 0) activity.finish()
} catch (e: DatabaseAccessException) {
// ...
}
}
private fun updateItemIds() {
itemIds = shapeIds.map { it.hashCode().toLong() }
}
override fun getItemId(position: Int): Long = shapeIds[position].hashCode().toLong()
override fun containsItem(itemId: Long): Boolean = itemIds.contains(itemId)
}
}

Add Drag and Drop on RecyclerView with DiffUtil

I have a list that gets updated from a Room Database. I receive the updated data from Room as a new list and I then pass it to ListAdapter's submitList to get animations for the changes.
list.observe(viewLifecycleOwner, { updatedList ->
listAdapter.submitList(updatedList)
})
Now, I want to add a drag and drop functionality for the same RecyclerView. I tried to implement it using ItemTouchHelper. However, the notifyItemMoved() is not working as ListAdapter updates its content through the submitList().
override fun onMove(
recyclerView: RecyclerView,
viewHolder: RecyclerView.ViewHolder,
target: RecyclerView.ViewHolder
): Boolean {
val from = viewHolder.bindingAdapterPosition
val to = target.bindingAdapterPosition
val list = itemListAdapter.currentList.toMutableList()
Collections.swap(list, from, to)
// does not work for ListAdapter
// itemListAdapter.notifyItemMoved(from, to)
itemListAdapter.submitList(list)
return false
}
The drag and drop now works fine but only when dragged slowly, when the dragging gets fast enough, I get different and inconsistent results.
What could be the reason for this? What is the best way that I can achieve a drag and drop functionality for my RecyclerView which uses ListAdapter?

So I made a quick test (this whole thing doesn't fit in a comment so I'm writing an answer)
My Activity contains the adapter, RV, and observes a viewModel. When the ViewModel pushes the initial list from the repo via LiveData, I save a local copy of the list in mutable form (just for the purpose of this test) so I can quickly mutate it on the fly.
This is my "onMove" implementation:
val from = viewHolder.bindingAdapterPosition
val to = target.bindingAdapterPosition
list[from] = list[to].also { list[to] = list[from] }
adapter.submitList(list)
return true
I also added this log to verify something:
Log.d("###", "onMove from: $from (${list[from].id}) to: $to (${list[to].id})")
And I noticed it.. works. But because I'm returning true (you seem to be returning false).
Now... unfortunately, if you drag fast up and down, this causes the list to eventually become shuffled:
E.g.: Let's suppose there are 10 items from 0-9.
You want to grab item 0 and put it between item 1 and 2.
You start Dragging item 0 at position 0, and move it a bit down so now it's between 1 and 2, the new item position in the onMove method is 1 (so far, you're still dragging). Now if you slowly drag further (to position 2), the onMove method is from 1 to 2, NOT from 0 to 2. This is because I returned "true" so every onMove is a "finished operation". This is fine, since the operations are slow and the ListAdapter has time to update and calculate stuff.
But when you drag fast, the operations go out of sync before the adapter has time to catch up.
If you return false instead (like you do) then you get various other effects:
The RecyclerView Animations don't play (while you drag) since the viewHolders haven't been "moved" yet. (you returned false)
The onMove method is then spammed every time you move your finger over a viewHolder, since the framework wants to perform this move again... but the list is already modified...
So you'd get something like (similar example above, 10 items, moving the item 0)> let's say each item has an ID that corresponds to its position+1 (in the initial state, so item at position 0 has id 1, item at position 1 has id 2, etc.)
This is what the log shows while I slowly drag item 0 "down":
(format is `from: position(id of item from) to: position(id of item to)
onMove from: 0 (1) to: 1 (2) // Initial drag of first item down to 2nd item.
onMove from: 0 (2) to: 1 (1) // now the list is inverted, notice the IDs.
onMove from: 0 (1) to: 1 (2) // Back to square one.
onMove from: 0 (2) to: 1 (1) // and undo-again...
I just cut it there, but you can see how it's bouncing all over the place back and forth. I believe this is because you return false but modify the list behind the scenes, so it's getting confused. on one side of the equation the "data" says one thing, (and so does the diff util), but on the other, the adapter is oblivious to this change, at least "yet" until the computations are done, which, as you guessed, when you drag super fast, is not enough time.
Unfortunately, I don't have a good answer (today) as to what would the best approach be. Perhaps, not relying on the ListAdapter's behavior and implementing a normal adapter, where you have better list/source control of the data and when to call submitList and when to simply notifyItemChanged or moved between two positions may be a better alternative for this use-case.
Apologies for the useless answer.

I ended up implementing a new adapter and use it instead of ListAdapter, as mentioned on Martin Marconcini's answer. I added two separate functions. One for receiving updates from Room database (replacement for submitList from ListAdapter) and another for every position change from drag
MyListAdapter.kt
class MyListAdapter(list: ArrayList<Item>) : RecyclerView.Adapter<RecyclerView.ViewHolder>() {
// save instance instead of creating a new one every submit
// list to save some allocation time. Thanks to Martin Marconcini
private val diffCallback = DiffCallback(list, ArrayList())
fun submitList(updatedList: List<Item>) {
diffCallback.newList = updatedList
val diffResult = DiffUtil.calculateDiff(diffCallback)
list.clear()
list.addAll(updatedList)
diffResult.dispatchUpdatesTo(this)
}
fun itemMoved(from: Int, to: Int) {
Collections.swap(list, from, to)
notifyItemMoved(from, to)
}
}
DiffCallback.kt
class DiffCallback(
val oldList: List<Item>,
var newList: List<Item>
) : DiffUtil.Callback() {
override fun getOldListSize(): Int {
return oldList.size
}
override fun getNewListSize(): Int {
return newList.size
}
override fun areItemsTheSame(oldItemPosition: Int, newItemPosition: Int): Boolean {
val oldItem = oldList[oldItemPosition]
val newItem = newList[newItemPosition]
return oldItem.id == newItem.id
}
override fun areContentsTheSame(oldItemPosition: Int, newItemPosition: Int): Boolean {
val oldItem = oldList[oldItemPosition]
val newItem = newList[newItemPosition]
return compareContents(oldItem, newItem)
}
}
Call itemMoved every position change:
override fun onMove(
recyclerView: RecyclerView,
viewHolder: RecyclerView.ViewHolder,
target: RecyclerView.ViewHolder
): Boolean {
val from = viewHolder.bindingAdapterPosition
val to = target.bindingAdapterPosition
itemListAdapter.itemMoved(from, to)
// Update database as well if needed
return true
}
When receiving updates from Room database:
You may also want to check if currently dragging using onSelectedChanged if you are also updating your database every position change to prevent unnecessary calls to submitList
list.observe(viewLifecycleOwner, { updatedList ->
listAdapter.submitList(updatedList)
})

I've tried danartillaga's answer and got a ConcurrentModificationException for the list variable. I use LiveData in the code and it looks like the data was changed during invalidation of the list.
I've tried to keep the ListAdapter implementation and concluded to the following solution:
class MyListAdapter : ListAdapter<Item, RecyclerView.ViewHolder>(MyDiffUtil) {
var modifiableList = mutableListOf<Item>()
private set
fun moveItem(from: Int, to: Int) {
Collections.swap(modifiableList, to, from)
notifyItemMoved(from, to)
}
override fun submitList(list: List<CourseData>?) {
modifiableList = list.orEmpty().toMutableList()
super.submitList(modifiableList)
}
}
and the onMove code from ItemTouchHelper.SimpleCallback:
override fun onMove(recyclerView: RecyclerView, viewHolder: RecyclerView.ViewHolder, target: RecyclerView.ViewHolder): Boolean {
val adapter = recyclerView.adapter as CoursesDownloadedAdapter
val from = viewHolder.bindingAdapterPosition
val to = target.bindingAdapterPosition
val list = adapter.modifiableList
// Change your DB here
adapter.moveItem(from, to)
return true
}
The magic here is saving the modifiableList inside the adapter. ListAdapter stores a link to the list from submitList call, so we can change it externally. During the Drag&Drop the list is changed with Collections.swap and RecyclerView is updated with notifyItemMoved with no DiffCallback calls. But the data inside ListAdapter was changed and the next submitList call will use the updated list to calculate the difference.

Drag & Dropping the first item of the RecyclerView moves several random positions

Currently, I have a RecyclerView implementing the new ListAdapter, using submitList to differ elements and proceed to update the UI automatically.
Lately i had to implement drag & drop to the list using the well known ItemTouchHelper. Here is my implementation, pretty straight forward:
class DraggableItemTouchHelper(private val adapter: DestinationsAdapter) : ItemTouchHelper.Callback() {
private val dragFlags = ItemTouchHelper.UP or ItemTouchHelper.DOWN
private val swipeFlags = 0
override fun isLongPressDragEnabled() = false
override fun isItemViewSwipeEnabled() = false
override fun getMovementFlags(recyclerView: RecyclerView, viewHolder: RecyclerView.ViewHolder): Int {
return makeMovementFlags(dragFlags, swipeFlags)
}
override fun onMove(
recyclerView: RecyclerView,
viewHolder: RecyclerView.ViewHolder,
target: RecyclerView.ViewHolder
): Boolean {
val oldPos = viewHolder.adapterPosition
val newPos = target.adapterPosition
adapter.swap(oldPos, newPos)
return true
}
override fun onSwiped(viewHolder: RecyclerView.ViewHolder, direction: Int) {
}
}
this is my swap function inside the adapter:
fun swap(from: Int, to: Int) {
submitList(ArrayList(currentList).also {
it[from] = currentList[to]
it[to] = currentList[from]
})
}
Everything works well EXCEPT when moving the FIRST item of the list. Sometimes it behaves OK, but most of the time (like 90%), it snaps several positions even when moving it slightly above the second item (to move 1st item on 2nd position for example). The new position seems random and i couldn't figure out the issue.
As a guide, i used the https://github.com/material-components/material-components-android example to implement Drag&Drop and for their (simple) list&layout works well. My list is a bit complex since it's inside a viewpager, using Navigation component and having many other views constrained together in that screen, but i don't think this should be related.
At this point i don't even know how to search on the web for this issue anymore.
The closest solution I found for this might be https://issuetracker.google.com/issues/37018279 but after implementing and having the same behaviour, I am thinking it's because I use ListAdapter which differs and updates the list asynchronously, when the solution uses RecyclerView.Adapter which uses notifyItemMoved and other similar methods.
Switching to RecyclerView.Adapter is not a solution.

This seems to be a bug in AsyncListDiffer, which is used under the hood by ListAdapter. My solution lets you manually diff changes when you need to. However, it's rather hacky, uses reflection, and may not work with future appcompat versions (The version I've tested it with is 1.3.0).
Since mDiffer is private in ListAdapter and you need to work directly with it, you'll have to create your own ListAdapter implementation(you can just copy the original source). And then add the following method:
fun setListWithoutDiffing(list: List<T>) {
setOf("mList", "mReadOnlyList").forEach { fieldName ->
val field = mDiffer::class.java.getDeclaredField(fieldName)
field.isAccessible = true
field.set(mDiffer, list)
}
}
This method silently changes the current list in the underlying AsyncListDiffer without triggering any diffing, as submitList() would.
The resulting file should look like this:
package com.example.yourapp
import androidx.recyclerview.widget.AdapterListUpdateCallback
import androidx.recyclerview.widget.AsyncDifferConfig
import androidx.recyclerview.widget.AsyncListDiffer
import androidx.recyclerview.widget.AsyncListDiffer.ListListener
import androidx.recyclerview.widget.DiffUtil
import androidx.recyclerview.widget.RecyclerView
abstract class ListAdapter<T, VH : RecyclerView.ViewHolder?> : RecyclerView.Adapter<VH> {
private val mDiffer: AsyncListDiffer<T>
private val mListener =
ListListener<T> { previousList, currentList -> onCurrentListChanged(previousList, currentList) }
protected constructor(diffCallback: DiffUtil.ItemCallback<T>) {
mDiffer = AsyncListDiffer(
AdapterListUpdateCallback(this),
AsyncDifferConfig.Builder(diffCallback).build()
).apply {
addListListener(mListener)
}
}
protected constructor(config: AsyncDifferConfig<T>) {
mDiffer = AsyncListDiffer(AdapterListUpdateCallback(this), config).apply {
addListListener(mListener)
}
}
fun setListWithoutDiffing(list: List<T>) {
setOf("mList", "mReadOnlyList").forEach { fieldName ->
val field = mDiffer::class.java.getDeclaredField(fieldName)
field.isAccessible = true
field.set(mDiffer, list)
}
}
open fun submitList(list: List<T>?) {
mDiffer.submitList(list)
}
fun submitList(list: List<T>?, commitCallback: Runnable?) {
mDiffer.submitList(list, commitCallback)
}
protected fun getItem(position: Int): T {
return mDiffer.currentList[position]
}
override fun getItemCount(): Int {
return mDiffer.currentList.size
}
val currentList: List<T>
get() = mDiffer.currentList
open fun onCurrentListChanged(previousList: List<T>, currentList: List<T>) {}
}
Now you need to change your adapter implementation to inherit from your custom ListAdapter rather than androidx.recyclerview.widget.ListAdapter.
Finally you'll need to change your adapter's swap() method implementation to use the setListWithoutDiffing() and notifyItemMoved() methods:
fun swap(from: Int, to: Int) {
setListWithoutDiffing(ArrayList(currentList).also {
it[from] = currentList[to]
it[to] = currentList[from]
})
notifyItemMoved(from, to)
}
An alternative solution would be to create a custom AsyncListDiffer version that lets you do the same without reflection, but this way seems easier. I will also file a feature request for supporting manual diffing out of the box and update the question with a Google Issue Tracker link.

I kept a copy of the items in my adapter, modified the copy, and used notifyItemMoved to update the UI as the user was dragging. I only save the updated items/order AFTER the user finishes dragging. This works for me because 1) I had a fixed length list of 9 items; 2) I was able to use clearView to know when the drag ended.
ListAdapter - kotlin:
var myItems: MutableList<MyItem> = mutableListOf()
fun onMove(fromPosition: Int, toPosition: Int): Boolean {
if (fromPosition < toPosition) {
for (i in fromPosition until toPosition) {
Collections.swap(myItems, i, i + 1)
}
} else {
for (i in fromPosition downTo toPosition + 1) {
Collections.swap(myItems, i, i - 1)
}
}
notifyItemMoved(fromPosition, toPosition)
return true
}
ItemTouchHelper.Callback() - kotlin:
// my items are only ever selected during drag, so when selection clears, drag has ended
override fun clearView(recyclerView: RecyclerView, viewHolder: RecyclerView.ViewHolder) {
super.clearView(recyclerView, viewHolder)
// clear drag style after item moved
viewHolder.itemView.requestLayout()
// trigger callback after item moved
val itemViewHolder = viewHolder as MyItemViewHolder
itemViewHolder.onItemMovedCallback(adapter.myItems)
}
MyItemViewHolder - kotlin
fun onItemMovedCallback(reorderedItems: List<MyItem>) {
// user has finished drag
// save new item order to database or submit list properly to adapter
}
I also had an itemOrder field on MyItem. I updated that field using the index of the re-ordered items when I saved it to the DB. I could probably update each items itemOrder field when I swap the items, but it seemed pointless (I just calculate the new order after the drag is finished).
I'm using LiveData from my database. I found the views "flickered" after the final database save because I changed the itemOrder on all the items and moved the items around in the adapter list. If this happens to you and you don't like it, just temporarily disable the recycler view item animator (I achieved this by setting it to null after the drag and restoring it after the list is updated in the RecyclerView/Adapter).
This worked for me and my specific case. Let me know if you need more details.