Develop Reference

RecyclerView ItemAnimator change order of moving items in default animation

I have a recyclerview that load a list of cards each one with a favorite button. When user touch that button I change the order of my list items setting to first position the new favorite card. That change displays the default animation when NotifyItemMoved is called but I want to display in front the item that is moving up. The default animation displays the item that is moving to botton in front of the rest of the items.
Searching a bit I found that I can implement a custom ItemAnimator and use something like this:
override fun animateMove(
holder: RecyclerView.ViewHolder?,
fromX: Int,
fromY: Int,
toX: Int,
toY: Int
): Boolean {
if ( fromY > toY) {
holder?.itemView?.bringToFront()
}
return super.animateMove(holder, fromX, fromY, toX, toY)
}
It looks that works well but when I scroll the list it crashes with this error: java.lang.RuntimeException: trying to unhide a view that was not hiddenandroidx.constraintlayout.widget.ConstraintLayout
If I remove holder?.itemView?.bringToFront() the default animation runs well again without any crash

The reason why you are getting the "trying to unhide a view that was not hidden" error is because the bringToFront() method of View can interfere with the RecyclerView's internal view recycling mechanism. When a view is recycled, it is hidden and re-used for another item in the list. By calling bringToFront() on a view, you are potentially interfering with this process and causing the view to be incorrectly re-used for a different item.
One way to avoid this issue is to create a custom RecyclerView.ItemAnimator that overrides the animateChange() method to bring the moved view to the front, but does not interfere with the view recycling process. Here's an example implementation:
class CustomItemAnimator : DefaultItemAnimator() {
override fun animateChange(
oldHolder: RecyclerView.ViewHolder?,
newHolder: RecyclerView.ViewHolder?,
preInfo: ItemHolderInfo?,
postInfo: ItemHolderInfo?
): Boolean {
if (oldHolder != null && newHolder != null) {
// Check if the item is being moved up (i.e. to a lower index)
if (oldHolder.adapterPosition > newHolder.adapterPosition) {
// Bring the new holder's item view to the front
newHolder.itemView.bringToFront()
}
}
return super.animateChange(oldHolder, newHolder, preInfo, postInfo)
}
}
This implementation only brings the new holder's item view to the front when the item is being moved up (i.e., to a lower index). This should allow the default RecyclerView view recycling mechanism to work correctly.
To use this custom ItemAnimator, set it on your RecyclerView using the setItemAnimator() method:
recyclerView.setItemAnimator(CustomItemAnimator())
Note: This implementation assumes that each item in the RecyclerView is represented by a single view in the ViewHolder. If you have complex item layouts with multiple views, you may need to modify this implementation to ensure that only the item view is brought to the front.

how to save state list in jetpack-navigation

I designed an app using jetpack-navigation
There is a problem as illustrated in the following image when I move from one fragment to another one the status of the list disappears.
In fact, when returning from a layout, the article will be re-created in the stack and the list status will not be saved and the user will have to scroll again. Please help me?
jetpack-navigation

The fragment gets recreated on every navigation operation. You could store the scroll position in your activity and load it from there. But doing it like this, the scroll position will be lost on activity recreate (e.g. rotating device).
Better approch would be to store it in a ViewModel. (see https://developer.android.com/topic/libraries/architecture/viewmodel)
The view model survives activity recreation and you can store your scroll position.
Then you can load this position and tell the list to scroll to this position (e.g. for RecyclerView with LinearLayoutManager by calling scrollToPositionWithOffset(...))

I'm reloading recyclerView data every 15s. To keep scroll position when switching between apps, I use onSaveInstanceState() and onRestoreInstanceState(mRVState) methods in corresponding fragment overriden methods. But when I wanted to save position while switching between different fragments, I came up with this solution:
1.Set RecyclerView.OnScrollListener() in onResume() method of Fragment and get current first visible item position on each scroll. As you can see position variable is located in parent activity, so it's not lost on fragment replacement:
override fun onResume() {
super.onResume()
if (updateListRunnable != null) setAndRunUpdateListRunnable()
mRV?.addOnScrollListener(object : RecyclerView.OnScrollListener() {
override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) {
super.onScrolled(recyclerView, dx, dy)
mainActivity.lastRVPosition =
(recyclerView.layoutManager as LinearLayoutManager).findFirstCompletelyVisibleItemPosition()
}
})
}
2.Use scrollToPosition() method of recyclerView after data has been replaced inside adapter:
private fun setDataList(dataList: List<Data?>?) {
val mutableDataList = dataList?.toMutableList()
val currentItemCount = binding?.rvDataList?.adapter?.itemCount
if (currentItemCount == null || currentItemCount == 0) {
// create new adapter with initial data
val adapter = DataListAdapter(mutableDataList, baseVM, mainVM)
binding?.rvDataList?.adapter = adapter
binding?.rvDataList?.layoutManager = LinearLayoutManager(context)
mRV?.scrollToPosition(mainActivity.lastRVPosition);
} else {
// update existing adapter with updated data
mRVState = mRV?.layoutManager?.onSaveInstanceState()
val currentAdapter = binding?.rvDataList?.adapter as? DataListAdapter
currentAdapter?.updateDataList(dataList)
currentAdapter?.notifyDataSetChanged()
mRV?.layoutManager?.onRestoreInstanceState(mRVState)
mRV?.scrollToPosition(mainActivity.lastRVPosition);
}
}
As you can see I also use onSaveInstanceState()/onRestoreInstanceState() before/after replacing data, so that if there was no scroll before data replacement, position will still be saved. Scroll listener saved position is only useful when switching between fragments.

RecyclerView's row item views hide/show getting messed up on scroll of the Recyclerview

I am using a RecyclerView to show list of products in my app, I need to group the product based on aisle. while the data are fetched for the first time in the list, the products are grouped correctly with respect to aisle. When we scroll the view, the aisle group divider is shown for the wrong item and the divider gets restored to correct position once the onBindViewHolder gets refreshed automatically.
MyAdapter.class
override fun onBindViewHolder(holder: ItemViewHolder, position: Int) {
itemsGrouping(pickItem, pickItemView, holder.adapterPosition)
}
private fun itemsGrouping(pickItem: PickItem, pickItemView: View, adapterPosition: Int) {
//Based on some condition
if(SomeCondition)
itemDivider(pickItemView,true)
else
itemDivider(pickItemView,false)
}
private fun itemDivider(v: View, boolean: Boolean) {
if(boolean) {
v.visibility = View.VISIBLE
} else {
v.visibility = View.GONE
}
}

Well, you should know that the view holders are reused in the RecyclerView, so it's probable not the right idea to try to determine the visibility of the divider in onBindViewHolder. I would recommend using item decorator for dividers. Here's the question and answer for that
How to add dividers and spaces between items in RecyclerView?

The problem is RecyclerView recycles previous views in order to be efficient.
I guess "SomeCondition" contains artifacts which are from previous holders.
So at
itemsGrouping(pickItem, pickItemView, holder.adapterPosition)
you should get pickItem and pickItemView from newly bound holder. You should use like
pickItemView = holder.findViewById(R.id.pickItemView);
Or consider using DataBinding Library
Here is a good example (it's in Kotlin) : DataBoundListAdapter
Once you extend your adapter to DataBoundListAdapter and override bind() method, everything inside bind is executed for every row, so you won't get repeated results.
Note : notice "executePendingBindings()"

when one card is deleted from RecyclerView one more card disappears along with it

I am having trouble debugging a recycler view issue. Here I am trying to delete an item from recycler view using the following method:
when I click on the card (one that is to be deleted), it will store the title of a card in shared preference. (so that in future when I open the app I will know what cards are not to be displayed)
Then I am calling a method which checks if the title in shared preference matches the title of the card and make ArrayList consisting of cards which are not present in shared preference.
Now I am using this ArrayList to fill cards using notifyDataSetChanged
My code is as Follows.
Adapter.
class LocalAdapter(var localCardsInfo : ArrayList<LocalModel>?,var fragment: LocalListingFragment) : RecyclerView.Adapter<LocalHolder>() {
fun refreshDataOnOrientationChange(mLocalCards : ArrayList<LocalModel>?){
if (localCardsInfo!!.size>0)
localCardsInfo!!.clear()
localCardsInfo = mLocalCards
notifyDataSetChanged()
}
override fun getItemCount(): Int {
return localCardsInfo!!.size
}
override fun onBindViewHolder(holder: LocalHolder, position: Int) {
if (localCardsInfo!=null)
holder.updateUI(holder.adapterPosition,localCardsInfo!![holder.adapterPosition])
}
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): LocalHolder {
val card_a : View = LayoutInflater.from(parent.context).inflate(R.layout.card_local_a,parent,false)
return LocalHolder(card_a,fragment)
}
}
ViewHolder
class LocalHolder(itemView : View,val fragment: LocalListingFragment) : RecyclerView.ViewHolder(itemView),OpenedLayoutManagerLocal{
fun updateUI(position : Int , localModel: LocalModel){
moveButton.setOnClickListener({
archived()
})
private fun archived(){
ALL_STATIC_CONSTANTS_AND_METHODS.addToArchive(fragment.activity!!,model!!.roomName,model!!.deviceName)
itemView.archiveLayout.visibility = View.GONE
itemView.elevateLayoutLocal.visibility = View.GONE
fragment.mAdapter!!.refreshDataOnOrientationChange(ArrayList(LocalDataService.ourInstance.getNonArchivedItems(fragment.activity!!)))
}
For example, if I have six item in recycler view and when I delete one I can see 5 items on the list while debugging, even onbind is called 5 times but only 4 items are displayed.
I tried my best to debug it yet failed to find a solution and I can't think about what to do next. I tried notifyItemRemoved and notifyItemRangeInserted also but still, I am facing the same issue. It would be a great help if someone can suggest a possible cause of such issue.
Thank you.
Edits:
I just experimented by adding dummy button in fragment where recycler view is placed. An to my surprise if I delete element here just element at that position gets deleted and there is no case of disappearing items. So it seems like problem happens when I delete an item from view holder. So I guess I got the cause of the error but can't think of a way to implement it because the original button is in the card so I am forced to use delete procedure inside view holder. Please do suggest if you have any suggestions. Code that I added in fragment is as follow:
v!!.findViewById<Button>(R.id.delete_button).setOnClickListener({
try {
val model = LocalDataService.ourInstance.getNonArchivedItems(activity!!)[0]
ALL_STATIC_CONSTANTS_AND_METHODS.addToArchive(activity!!,model.roomName,model.deviceName)
mAdapter!!.refreshDataOnOrientationChange(ArrayList(LocalDataService.ourInstance.getNonArchivedItems(activity!!)))
}catch (e : Throwable){}
})
Here on this new dummy button click, it deletes the first item in the list gets deleted while on clicking the button on RecyclerView card it deletes one item and then one more item gets disappeared.

How to use DiffUtil.Callback with a RecyclerView that has header and footer?

Background
I work on an app that has a RecyclerView which you can scroll up and down however you wish.
The data items are loaded from the server, so if you are about to reach the bottom or the top, the app gets new data to show there.
To avoid weird scrolling behavior, and staying on the current item, I use 'DiffUtil.Callback' , overriding 'getOldListSize', 'getNewListSize', 'areItemsTheSame', 'areContentsTheSame'.
I've asked about this here, since all I get from the server is a whole new list of items, and not the difference with the previous list.
The problem
The RecyclerView doesn't have only data to show. There are some special items in it too:
Since Internet connection might be slow, there is a header item and a footer item in this RecyclerView, which just have a special Progress view, to show you've reached the edge and that it will get loaded soon.
The header and footer always exist in the list, and they are not received from the server. It's purely a part of the UI, just to show things are about to be loaded.
Thing is, just like the other items, it needs to be handled by DiffUtil.Callback, so for both areItemsTheSame and areContentsTheSame, I just return true if the old header is the new header, and the old footer is the new footer:
override fun areItemsTheSame(oldItemPosition: Int, newItemPosition: Int): Boolean {
val oldItem = oldItems[oldItemPosition]
val newItem = newItems[newItemPosition]
when {
oldItem.itemType != newItem.itemType -> return false
oldItem.itemType == ItemType.TYPE_FOOTER || oldItem.itemType == AgendaItem.TYPE_HEADER -> return true
...
}
}
override fun areContentsTheSame(oldItemPosition: Int, newItemPosition: Int): Boolean {
val oldItem = oldItems[oldItemPosition]
val newItem = newItems[newItemPosition]
return when {
oldItem.itemType == ItemType.TYPE_FOOTER || oldItem.itemType == ItemType.TYPE_HEADER -> true
...
}
}
}
Seems right? Well it's wrong. If the user is at the top of the list, showing the header, and the list gets updated with new items, the header will stay at the top, meaning the previous items you've seen will get pushed away by the new ones.
Example:
Before: header, 0, 1, 2, 3, footer
After: header, -3, -2, -1, 0, 1, 2, 3, footer
So if you stayed on the header, and the server sent you the new list, you still see the header, and below the new items, without seeing the old ones. It scrolls for you instead of staying on the same position .
Here's a sketch showing the issue. The black rectangle shows the visible part of the list.
As you can see, before loading, the visible part has the header and some items, and after loading it still has the header and some items, but those are new items that pushed away the old ones.
I need the header to be gone on this case, because the real content is below it. Instead of the area of the header, it might show other items (or a part of them) above it, but the visible position of the current items should stay where they are.
This issue only occurs when the header is shown, at the top of the list. In all other cases it works fine, because only normal items are shown at the top of the visible area.
What I've tried
I tried to find how to set DiffUtil.Callback to ignore some items, but I don't think such a thing exists.
I was thinking of some workarounds, but each has its own disadvantages:
A NestedScrollView (or RecyclerView) which will hold the header&footer and the RecyclerView in the middle, but this might cause some scrolling issues, especially due to the fact I already have a complex layout that depends on the RecyclerView (collapsing of views etc...).
Maybe in the layout of the normal items, I could put the layout of the header and footer too (or just the header, because this one is the problematic one). But this is a bad thing for performance as it inflates extra views for nothing. Plus it requires me to toggle hiding and viewing of the new views within.
I could set a new ID for the header each time there is an update from the server, making it as if the previous header is gone, and there is a totally new header at the top of the new list. However, this might be risky in the case of no real updates of the list at the top, because the header will be shown as if it's removed and then re-added.
The questions
Is there a way to solve this without such workarounds?
Is there a way to tell DiffUtil.Callback : "these items (header&footer) are not real items to scroll to, and these items (the real data items) should be" ?

I will try to explain what I see as a solution to your problem:
Step 1: Remove all the code for FOOTER and HEADER views.
Step 2: Add these methods that add and remove dummy model items in adapter based on the user scroll direction:
/**
* Adds loader item in the adapter based on the given boolean.
*/
public void addLoader(boolean isHeader) {
if (!isLoading()) {
ArrayList<Model> dataList = new ArrayList<>(this.oldDataList);
if(isHeader) {
questions.add(0, getProgressModel());
else {
questions.add(getProgressModel());
setData(dataList);
}
}
/**
* Removes loader item from the UI.
*/
public void removeLoader() {
if (isLoading() && !dataList.isEmpty()) {
ArrayList<Model> dataList = new ArrayList<>(this.oldDataList);
dataList.remove(getDummyModel());
setData(questions);
}
}
public MessageDetail getChatItem() {
return new Model(0, 0, 0, "", "", "")); // Here the first value is id which is set as zero.
}
And here is your rest of the adapter logic that you need to decide if the item is a loader item or an actual data item:
#Override
public int getItemViewType(int position) {
return dataList.get(position).getId() == 0 ? StaticConstants.ItemViewTypes.PROGRESS : StaticConstants.ItemViewTypes.CONTENT;
}
According to the view type, you can add a progress bar view holder in your adapter.
Step 3: use these methods in data loading logic:
While making the API call in onScrolled() method of recyclerView, you need to add a loader item before the api call and then remove it after the api call. Use the given adapter methods above. The coded in onScrolled should look a little like this:
recyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
#Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
if (dy < 0) { //This is top scroll, so add a loader as the header.
recyclerViewAdapter.addLoader(true);
LinearLayoutManager linearLayoutManager = (LinearLayoutManager) recyclerView.getLayoutManager();
if (!recyclerViewAdapter.isLoading(true)) {
if (linearLayoutManager.findFirstCompletelyVisibleItemPosition() <= 2) {
callFetchDataApi();
}
}
}
} else {
if (!recyclerViewAdapter.isLoading(false)) {
if (linearLayoutManager.findLastCompletelyVisibleItemPosition() >= linearLayoutManager.getItemCount() - 2) {
callFetchDataApi();
}
}
});
Now after the api call gives you the data you need. Simply remove the added loader from the list like this:
private void onGeneralApiSuccess(ResponseModel responseModel) {
myStreamsDashboardAdapter.removeLoader();
if (responseModel.getStatus().equals(SUCCESS)) {
// Manage your pagination and other data loading logic here.
dataList.addAll(responseModel.getDataList());
recyclerViewAdapter.setData(dataList);
}
}
And lastly, you need to avoid any scroll during data loading operation is add a logic method for that is isLoading() method. which is used in the code of method onScrolled():
public boolean isLoading(boolean isFromHeader) {
if (isFromHeader) {
return dataList.isEmpty() || dataList.get(0).getId() == 0;
} else {
return dataList.isEmpty() || dataList.get(dataList.size() -1).getId() == 0;
}
}
Let me know if you don't understand any of this.

I think for now, the solution I took will suffice. It's a bit weird, but I think it should work:
The header item gets a new id each time the list is different in its first real item. The footer always have the same id, because it's ok for it to move in the current way it works. I don't even need to check that its id is the same. The check of areItemsTheSame is as such for them:
oldItem.agendaItemType == AgendaItem.TYPE_HEADER -> return oldItem.id == newItem.id
oldItem.agendaItemType == AgendaItem.TYPE_FOOTER -> return true
This way, if the header belongs to a new list data, old one will be removed, and new one will be at the top.
It's not the perfect solution, as it doesn't really push the original header to be at the top, and theoretically it makes us "kinda" have 2 headers at the same time (one being removed and one being added) but I think it's good enough.
Also, for some reason, I can't use notifyItemChanged on the header and footer in case only they get updated (internet connection changes its state, so need to change the header&footer alone). Only notifyDataSetChanged works for some reason.
Still, if there is a more official way, could be nice to know.