Develop Reference

how to make recycler view not scroll back to top after update

I have recycler view with datas that when it on the bottom with this code findLastCompletelyVisibleItemPosition() it will load new data. my init data and my load data are the same function just add change the body request after recyclerview scroll to very bottom. My issue is when it load a new datas it will scroll back to top. how do I make it in the same place and not scroll back?
I already tried to impelemnt this in load data function
val recyclerViewState =list_view_history_program.layoutManager?.onSaveInstanceState()
if (loadMore > 0) {
listAdapter.notifyItemRangeChanged(loadMoreCount, listAdapter.itemCount, programNames)
listAdapter.notifyDataSetChanged()
list_view_history_program.layoutManager?.onRestoreInstanceState(recyclerViewState)
list_view_history_program.scrollToPosition(loadMoreCount)
}
but still it scroll back. please help

You already used notifyItemRangeChanged then used notifyDataSetChanged. Remove listAdapter.notifyDataSetChanged()

Use below code after add item in itemList array
NOTE : but you must call adapter the first time then second time use the below code
adapter.notifyItemInserted(itemList.size());

Is there an event called by changing the count of items in the recyclerview?

Is there an event called by changing the count of items in the recyclerview?
I want to call function every time recyclerview items are added.

Update:
It turns out I misunderstood the original question. What was really asked is how to get notified when the underlying data in an Adapter has changed.
For this you could use a RecyclerView.AdapterDataObserver in conjunction with RecyclerView.Adapter's registerAdapterDataObserver(AdapterDataObserver observer) method to register for changes in the underlying list data.
Original Answer:
Your RecyclerView is backed by a RecyclerView.Adapter which owns the actual list of items being displayed.
If you change the backing list, you should call one of the notifyXXX methods on your adapter to notify your RecyclerView what has changed (and optionally where in the list the change happened.)
At the very least, you could call notifyDataSetChanged on your adapter to tell your RecyclerView that something somewhere in the list has changed. This can be expensive since you're not being specific about what changed, so the RecyclerView has to query the adapter for more information and potentially redraw its entire client area of items.
Something like:
RecyclerView.Adapter adapter = recyclerView.getAdapter();
if (adapter != null) {
adapter.notifyDataSetChanged();
}
Behind the scenes, the RecyclerView will call the RecyclerView.Adapter#getItemCount() method on the Adapter to determine what the current item count is.

How to check if item in RecyclerView Adapter is still visible after async callback

I want to update one item calling asynchronous call to server API inside onBindViewHolder. I send item at position + position into the callback. Response call arrives in 20 seconds into callback funcion. Into the callback function is returned response and position. Then I call notifyItemChanged(pos, response). And inside payload onBindViewHolder I update item on that position and its View. Problem is that if async request takes 20 seconds and user will scroll quickly throught RecyclerView it will update wrong item View because that view at position could be unbound or could be bound to other item from list.
Is there any way how to track which item at which position is unbound to cancel request? I have to update this one info after adapter is created, because if I will do that before, user will not see any recyclerView item for almost 2 minutes till my list is ready. (only this one call is taking so long).

I wouldn't pass the position as context. I would pass an identifier. Could be an internal integer as id or something. Then you can easily determine which id's are currently visible on the screen and see if that list contains the id of the calback.

I am not sure about your question, but you could work onto your items directly in your adapter.
Then you do:
Adapter adapter = new BaseAdapter(newDataset);
recyclerView.setAdapter(adapter);
recyclerView.notifyDataSetChanged();
Otherwise, if your really work on views rather than dataset, you can do this:
in your adapter:
create a View array
create a custom function View getViewAtPos(int pos)
check if your view is visible in your current scrollview (here)

Load image via URL into RecyclerAdapter

I have an API which returns JSON and I would like to load an Image from a URL which is provided by this API. The Image should be passed into Adapter for a Recycling View.
Right now all Items which contain an Imgae_URL are getting skipped by my Adapter and I dont really understand why.
if (json_img_url.isNotEmpty()) {
Executors.newSingleThreadExecutor().execute({
val conn = URL(json_img_url).openConnection()
conn.connect()
val iStream:InputStream = conn.getInputStream()
val img_bitmap:Bitmap? = BitmapFactory.decodeStream(iStream)
newItems.add(Item(....img_bitmap))
})
....
itemArrayAdapter.addItems(newItems)
URL :"https://s3.us-east-2.amazonaws.com/c...."
The URls used are valid and Images on the S3 Bucket are all public.
The If statment returns true (I checked with Log.d) but the Item does not appear on the Phone, I dont recive an error and the app does not crash its just like the Item was never there...
I know there are librarys like Picasso or Glide but even with them I could not make it work and to be honest I would like to accomplish this task without a having to install an extra package, it just feels wrong.

Unlike ListView, there is no way to add or remove items directly through the RecyclerView adapter. You need to make changes to the data source directly and notify the adapter of any changes.There are many method available to use when notifying the adapter of different changes:
notifyItemChanged(int pos) : Notify that item at position has changed.
notifyItemInserted(int pos): Notify that item reflected at position has been newly inserted.
notifyItemRemoved(int pos): Notify that items previously located at position has been removed from the data set.
notifyDataSetChanged(): Notify that the dataset has changed. Use only as last resort.
Every time we want to add or remove items from the RecyclerView, we will need to explicitly inform to the adapter of the event. Unlike the ListView adapter, a RecyclerView adapter should not rely on notifyDataSetChanged() since the more granular actions should be used. See the API documentation for more details.
Also, if you are intending to update an existing list, make sure to get the current count of items before making any changes. For instance, a getItemCount() on the adapter should be called to record the first index that will be changed.
// record this value before making any changes to the existing list
int curSize = itemArrayAdapter.getItemCount();
// update the existing list
newItems.add(Item(....img_bitmap));
// curSize should represent the first element that got added
// newItems.size() represents the itemCount
itemArrayAdapter.notifyItemRangeInserted(curSize, newItems.size());

Google I/O 2010 - The world of ListView notifyDataSetChanged()

sorry for stupid question. But really interesting and incomprehensible. In this session discussed about notifyDataSetChanged() method.
From documentation for this method - "called when the data set being observed has changed, and which when read contains the new state of the data". My English bad and I do not understand all. But I right if guess that method called when I need refresh ListView with new data set?
If I'm right then I'm confused. In the past and my first program I played with contacts api of android. And run some processing in an asynctask. At this time appeared dialog with progress bar and in the background, you could see how the state of ListView changed in real time. Data for ListView row changed via BindView.
Why? So I'm in something wrong. Explain please.

As i read it, BindView is only used with cursors, which are a specific type of a data set basically. You can have alternative data sets, there is for example an ArrayListAdapter in the API which uses an ArrayList as its dataset. In case that data set changes, notifyDataSetChanged() will have to be called to notify the list view that its bounds will have to be recalculated and its views have to be redrawn (and probably some more).
If you decide to write your own and create the possibility to modify the data shown in the list view through an adapter (one could imagine adding method like addObject(SomeObject o) in your home made adapter for example), then you'd call notifyDataSetChanged() in that method.
Similarly if you have a deleteObject(SomeObject x), if the remaining data set is larger than zero you'd call notifyDataSetChanged() or when the remaining data set is empty you'd call notifyDataSetInvalidated() which in turn will to some extra stuff like setting the so called empty view in the list if you have one specified.