Develop Reference

How to stop the RecyclerView OnBindViewHolder() function iterating through all items of my ArrayList every time a new item is added?

I'm trying to make a simple chat application for my own learning - no firebase involved (the messages won't be stored between sessions). I've implemented a RecyclerView to show all the messages. The problem is that every time I add a new message, the RecyclerView Adapter will iterate through all previous messages before populating the latest one. Whilst this isn't causing any major bugs, it does seem very inefficient. The relevant functions in my adapter class are shown below:
#Override
public void onBindViewHolder(#NonNull ViewHolder holder, int position) {
MessageItem newMsgItem = messages.get(position);
holder.txtMsgContent.setText(newMsgItem.getMsgContent());
RelativeLayout.LayoutParams layoutParams = (RelativeLayout.LayoutParams) holder.msgParentView.getLayoutParams();
if (newMsgItem.isSent()) {
layoutParams.addRule(RelativeLayout.ALIGN_PARENT_RIGHT);
holder.msgParentView.setLayoutParams(layoutParams);
holder.msgParentView.setCardBackgroundColor(0xFF03DAC5);
} else {
layoutParams.addRule(RelativeLayout.ALIGN_PARENT_LEFT);
holder.msgParentView.setLayoutParams(layoutParams);
holder.msgParentView.setCardBackgroundColor(0xFF67706F);
}
}
// boolean sent: false = received, true = sent
public void addMessage (boolean sent, String msgContent) {
messages.add(new MessageItem(sent, msgContent));
notifyDataSetChanged();
}
I could implement a condition-check like below, but that isn't a satisfying solution as it only masks the problem - i.e. the program is still iterating unnecessarily through all previous messages:
#Override
public void onBindViewHolder(#NonNull ViewHolder holder, int position) {
if (position == messages.size() - 1) {
//... do function
}
}
Is there a way to make the program only call onBindViewHolder for the newest item that's been added? I also saw this forum, but as I'm a beginner I couldn't tell if they were having the same issue as me.
RecyclerView populating each item every time i add a new item

notifyDataSetChanged() always reloads the whole view. Use notifyItemInserted() instead.
public void addMessage (boolean sent, String msgContent) {
messages.add(new MessageItem(sent, msgContent));
notifyItemInserted(messages.size()-1);
}

Don't use notifyDataSetChanged() method, you can use notifyItemInserted() method, this will not refresh every time.
public void addMessage (boolean sent, String msgContent) {
messages.add(new MessageItem(sent, msgContent));
notifyItemInserted(messages.size()-1);}

How To Save State Of RecyclerView Checkbox On Screen Rotation

On screenrotation the selected items get unselected, I want to save its state.
I have all these forms in recyclerView which get selected on click. This is the code in onListItemClick
private void onListItemClick(View view, int position) {
Cursor cursor = instanceAdapter.getCursor();
cursor.moveToPosition(position);
CheckBox checkBox = view.findViewById(R.id.checkbox);
checkBox.setChecked(!checkBox.isChecked());
long id = cursor.getLong(cursor.getColumnIndex(InstanceProviderAPI.InstanceColumns._ID));
if (selectedInstances.contains(id)) {
selectedInstances.remove(id);
} else {
selectedInstances.add(id);
}
Bundle bundle=new Bundle();
sendButton.setEnabled(selectedInstances.size() > 0);
toggleButtonLabel();
}
where selectedInstances is a LinkedHashSet
private LinkedHashSet<Long> selectedInstances;
Here is the GIF

Unless you can store it in a database or anything that's 'persistent', then you could just keep a list/array of booleans with as many entries as your ListView. When you check the second checkbox, set array[1] = true.
Then in your adapter you just check the state of the position of the list for the current item.
Somewhat of an example
boolean[] checkedState = new boolean[list.count];
private void onListItemClick(View view, int position) {
//...
checkedState[position] = //checked state
}
//adapter
public void onBindViewHolder(#NonNull final RecyclerView.ViewHolder holder, int position) {
//...
checkBox.isChecked = checkedState[position]
}

ViewModel Stores UI-related data that isn't destroyed on app rotations.

Regarding to keep UI states you can use the methods onSaveInstanceState() and onRestoreInstanceState of activity object for save that data in the Bundle type parameter as follow bellow:
protected void onSaveInstanceState(Bundle state) {
super.onSaveInstanceState(state);
String setting;
state.putString("KeyName", setting);
}
protected void onRestoreInstanceState(Bundle state) {
super.onRestoreInstanceState(state);
String setting;
setting = state.getString("KeyName");
}
The most correct way according to Android Developer Documentation's to persist that data, so when the app's finished and then it's started again the app will can retrieve that data from local storage.
It can be by SharedPreferences or Room database depending on data complexity. Like the data are settings, so I believe you'll want to store one when you had finished your app and to retrieve one when you start you app again.
References:
Saving UI States
SharedPreferences
Save key-value data
Save data in a local database using Room
RoomDatabase
Android Jetpack: Room
What’s New in Room (Android Dev Summit '19)

how to update recyclerview after pulling data from server?

If i had to send a request to get data within onBindViewHolder(), how can i update view after data comes back from server?
what I have now is that I cache the data along with row position, so that next time when user scrolls to that row, I can display info right away.
but there are 2 other issues I don't know how to solve.
I scroll the list to view item at position 10, 11 and 12. I decided to wait for data to come back. do i call notifyDataSetChanged() after? because onBindViewHolder already been called by the time data comes back and view would just remained empty, but I also don't think by calling notifyDataSetChanged() after each request would be a good idea.
I start to view the list at position 0 and keep scrolling to position 10. app sends out request to pull data for position 0 to 10. since the request at 0 is sent out first, more likely it would get back first or at least sooner than position 10, but by that time I'm already viewing the item at position 10. my view would start changing if all requests are back in order, so it would show data for position 0 then keep updating all the way to 10.
is it a bad practice to load data from server as recyclerview scrolls? but by doing this would save me a lot of time, and I guess for user too? because instead of sending all the requests ahead of time, user get to see partial data while other data are being loaded in the background.
Thanks!!!
EDITED
public class TestAdapter extends RecyclerView.Adapter<TestAdapter.ViewHolder> {
private Context ctx;
private ArrayList<Photo> alPhotos = new ArrayList<>();
private HashMap<String, Drawable> hmImages = new HashMap<>();
public TestAdapter(Context ctx, ArrayList<Photo> alPhotos) {
this.ctx = ctx;
this.alPhotos = alPhotos;
}
#Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
return new ViewHolder(LayoutInflater.from(parent.getContext()).inflate(R.layout.item_photo_brief, parent, false));
}
#Override
public void onBindViewHolder(ViewHolder holder, int position) {
Photo photo = alPhotos.get(position);
loadRemoteImage(photo.IMG, holder.ivThumb, true);
holder.tvEmail.setText(photo.EMAIL);
}
#Override
public int getItemCount() {
return alPhotos.size();
}
private void loadRemoteImage(final String imgUrl, final ImageView view, final boolean cache) {
if (hmImages.containsKey(imgUrl)) {
view.setImageDrawable(hmImages.get(imgUrl));
} else {
final WeakReference<ImageView> weakView = new WeakReference<>(view);
RequestManager.getManager().add(new Request<>(imgUrl, new DrawableParser(), new RequestCallback<Drawable>() {
#Override
public void onFinished(Request<Drawable> request, Response<Drawable> response) {
if (cache) hmImages.put(imgUrl, response.result);
ImageView view = weakView.get();
if (view != null) {
view.setImageDrawable(response.result);
}
}
#Override
public void onError(Request<Drawable> request, Response<Drawable> response) {
}
#Override
public void onTimeout(Request<Drawable> request, Response<Drawable> response) {
}
})
);
}
}
public class ViewHolder extends RecyclerView.ViewHolder {
private ImageView ivThumb;
private TextView tvEmail;
public ViewHolder(View itemView) {
super(itemView);
findViews();
}
private void findViews() {
ivThumb = (ImageView) itemView.findViewById(R.id.ivThumb);
tvEmail = (TextView) itemView.findViewById(R.id.tvEmail);
}
}
}

It's a good idea to load data while scrolling, a lot of popular apps do that. I personally use WeakReference in this case. I store a weak reference to the view holder in my model when I start loading data. If the reference is still valid by the time I get the response then it makes sense to update the view. If there is no view holder in memory then it's already been recycled and I don't have to update anything anymore.
When onViewRecycled is called you can clear the weak reference and also consider cancelling the network request (depends on your needs).
Caching works perfect with this model, you just insert this logic before making a network request. Again, this depends on your needs, maybe you don't need caching at all, or maybe your data is rarely updated then it makes sense to always use cache until some event.
In my app I also use EventBus, it helps me with event handling, but it is absolutely fine to just use Android SDK and support library.
You can also add a ScrollListener if you need to differentiate the item behavior depending on whether user scrolls the list right now. E.g. in my app I animate the data if list loaded and user wasn't scrolling it (improves interaction with the user). When user scrolls I load data as is, because it will be too much motion on the screen if I animate data.

ParseQueryAdapter; using class in Android

I feel like a broken record.
After many attempts, I have failed at getting a listview through Parse data to display a specific set of information.
Here is my model...this is all data from users:
#ParseClassName("Midwifefirm")
public class Midwifefirm extends ParseObject {
public Midwifefirm() {
// A default constructor is required.
}
//practice name
public String getPracticeName() {
return getString("practicename");
}
public void setPracticeName(String practicename) {
put("practicename", practicename);
}
//education
public String getEducation() {
return getString("education");
}
public void setEducation(String education) {
put("education", education);
}
//years in practice
public String getYearsinPractice() {
return getString("yearsinpractice");
}
public void setYearsinPractice(String yearsinpractice) {
put("yearsinpractice", yearsinpractice);
}
//practice philosophy
public String getPracticePhilosophy() {
return getString("practicephilosophy");
}
public void setPracticePhilosophy(String practicephilosophy) {
put("practicephilosophy", practicephilosophy);
}
I have this adapter; I am wondering what to place in the query section, as I just want to pull the data into the ListView that is defined in the data model:
public class CustomMidwifeAdapter extends ParseQueryAdapter<Midwifefirm> {
public CustomMidwifeAdapter(Context context) {
super(context, new ParseQueryAdapter.QueryFactory<Midwifefirm>() {
public ParseQuery<Midwifefirm> create() {
// Here we can configure a ParseQuery to display
// only top-rated meals.
ParseQuery query = new ParseQuery("Midwives");
return query;
}
});
}
#Override
public View getItemView(Midwifefirm midwifefirm, View view, ViewGroup parent) {
if (view == null) {
view = View.inflate(getContext(), R.layout.activity_midwife_result_list, null);
}
//use midwifefirm as item view/list
super.getItemView(midwifefirm, view, parent);
// find in layout the practice name
TextView titleTextView = (TextView) view.findViewById(R.id.practicename);
//in the midwifefirm data model, call getPracticename
titleTextView.setText(midwifefirm.getString("practicename"));
// Add education view
TextView EducationView = (TextView) view.findViewById(R.id.education);
EducationView.setText(midwifefirm.getString("education"));
// Add yearsexperience view
TextView ExperienceView = (TextView) view.findViewById(R.id.yearsinpractice);
ExperienceView.setText(midwifefirm.getString("yearsinpractice"));
//Add practice philosophy view
TextView PracticePhilosophyView = (TextView) view.findViewById(R.id.practicephilosophy);
PracticePhilosophyView.setText(midwifefirm.getString("practicephilosophy"));
return view;
}
}
And here is the Main Activity:
public class MidwifeResultList extends ListActivity {
private ParseQueryAdapter<ParseObject> mainAdapter;
private CustomMidwifeAdapter midwifeListAdapter;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//initialize main ParseQueryAdapter
mainAdapter = new ParseQueryAdapter<ParseObject>(this, Midwifefirm.class);
//which keys in Midwife object
mainAdapter.setTextKey("practicename");
mainAdapter.setTextKey("education");
mainAdapter.setTextKey("yearsinpractice");
mainAdapter.setTextKey("practicephilosophy");
// Initialize the subclass of ParseQueryAdapter
midwifeListAdapter = new CustomMidwifeAdapter(this);
// Default view is all meals
setListAdapter(mainAdapter);
}
Every time I run this, I get no results.
Thanks in advance for any help
Michael

I can tell you why I think it fails now and I can tell you why I'm very sure it will fail after you sort out the current issue.
It seems that you're trying to use different classes
#ParseClassName("Midwifefirm")
public class Midwifefirm extends ParseObject {
and
ParseQuery query = new ParseQuery("Midwives");
You need to be consistent and use the same name. Either use Midwives or Midwifefirm for both. Let's assume you picked the latter. You're also saying
all that is stored in the user table...wasn't sure if I needed to create new tables.
The query above wants to get all entries of type Midwives. If there's no such type, it'll return nothing. So you have two options:
In you Parse dashboard, reate a class Midwifefirm (don't forget to update the String inside #ParseClassName above) and store your Midwifefirm data in there. You don't need to change your query for this.
Add a column to your ParseUser class, such as type, that you can set to Midwifefirm or whatever if that user is a Midwifefirm or whatever. Then in your query you need to add:
ParseQuery query = new ParseQuery("Midwives");
query.whereEquals("type", "Midwifefirm");
I greatly prefer the former.
Anyway, once your done that, the issue is that you're not using a custom view for this. You're relying on the one provided by Android by default for ListActivity. I am fairly sure it doesn't have any of the fields you're after, so you should create a custom view for this, then at the top of onCreate in your Activity make sure you use it
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.my_custom_view);
By the way, the following are redundant if you populate then in getItemView anyway:
mainAdapter.setTextKey("practicename");
mainAdapter.setTextKey("education");
mainAdapter.setTextKey("yearsinpractice");
mainAdapter.setTextKey("practicephilosophy");
One final advice: if you're still having issues, set breakpoints and do some investigations first. What you need to check is:
Whether you get anything at all from Parse when you do your query. Your adapter has an useful addOnQueryLoadListener that you may use to check whether anything's been retrieved at all.
If stuff is retrieved successfully, you need to check whether the list view is populated correctly. Again, use breakpoints, this time in getItemView maybe.

I'm going to do a wild guess here using the lovely brainwrecking API help of Parse.com about ParseQueryAdapters
Before continuing, may I mind you that my experience with ParseQueryAdapters is a minimum but I think I have a basic knowledge about them + I have some experience with Parse on its own. ANYHOW,
As an example they use both these
final ParseQueryAdapter adapter = new ParseQueryAdapter(this, "Midwives");
adapter.setTextKey("name");
ListView listView = (ListView) findViewById(R.id.listview);
listView.setAdapter(adapter);
and
// Instantiate a QueryFactory to define the ParseQuery to be used for fetching items in this
// Adapter.
ParseQueryAdapter.QueryFactory<ParseObject> factory =
new ParseQueryAdapter.QueryFactory<ParseObject>() {
public ParseQuery create() {
ParseQuery query = new ParseQuery("Midwives");
return query;
}
};
// Pass the factory into the ParseQueryAdapter's constructor.
ParseQueryAdapter<ParseObject> adapter = new ParseQueryAdapter<ParseObject>(this, factory);
adapter.setTextKey("name");
// Perhaps set a callback to be fired upon successful loading of a new set of ParseObjects.
adapter.addOnQueryLoadListener(new OnQueryLoadListener<ParseObject>() {
public void onLoading() {
// Trigger any "loading" UI
}
public void onLoaded(List<ParseObject> objects, ParseException e) {
// Execute any post-loading logic, hide "loading" UI
}
});
// Attach it to your ListView, as in the example above
ListView listView = (ListView) findViewById(R.id.listview);
listView.setAdapter(adapter);
To start of, the reason why I think nothing is loading inside your list has to do with a little mixup between the initilization of your ParseQueryAdapter and your custom adapter.
You configure the basic adapter, and also initialize a custom adapter but you don't do anything with the custom adapter, tho the custom adapter seems to contain the logics to load your data model.
I think what you're looking for is something like this:
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//initialize main ParseQueryAdapter
mainAdapter = new CustomMidwifeAdapter<ParseObject>(this);
//which keys in Midwife object
mainAdapter.setTextKey("practicename");
mainAdapter.setTextKey("education");
mainAdapter.setTextKey("yearsinpractice");
mainAdapter.setTextKey("practicephilosophy");
// Default view is all meals
setListAdapter(mainAdapter);
}
All you need to pass is the context (aka "this"), and the constructor of your custom class will handle the factory internal
super(context, new ParseQueryAdapter.QueryFactory<Midwifefirm>() {
public ParseQuery<Midwifefirm> create() {
// Here we can configure a ParseQuery to display
// only top-rated meals.
ParseQuery query = new ParseQuery("Midwives");
return query;
}
});
Tho to be honest since you do:
new ParseQueryAdapter<ParseObject>(this, Midwifefirm.class);
I wonder if you'd need to change your "QueryFactory" to
super(context, new ParseQueryAdapter.QueryFactory<Midwifefirm>() {
public ParseQuery<Midwifefirm> create() {
// Here we can configure a ParseQuery to display
// only top-rated meals.
ParseQuery query = new ParseQuery(MidWifefirm.class);
return query;
}
});
Where you pass a class to the the query rather than the tableName, but I could be wrong on that one.
Either way I hope this has helped in some way!

notifyDataSetChanged not working on RecyclerView

I am getting data from server and then parsing it and storing it in a List. I am using this list for the RecyclerView's adapter. I am using Fragments.
I am using a Nexus 5 with KitKat. I am using support library for this. Will this make a difference?
Here is my code: (Using dummy data for the question)
Member Variables:
List<Business> mBusinesses = new ArrayList<Business>();
RecyclerView recyclerView;
RecyclerView.LayoutManager mLayoutManager;
BusinessAdapter mBusinessAdapter;
My onCreateView():
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Getting data from server
getBusinessesDataFromServer();
View view = inflater.inflate(R.layout.fragment_business_list,
container, false);
recyclerView = (RecyclerView) view
.findViewById(R.id.business_recycler_view);
recyclerView.setHasFixedSize(true);
mLayoutManager = new LinearLayoutManager(getActivity());
recyclerView.setLayoutManager(mLayoutManager);
mBusinessAdapter = new BusinessAdapter(mBusinesses);
recyclerView.setAdapter(mBusinessAdapter);
return view;
}
After getting data from server, parseResponse() is called.
protected void parseResponse(JSONArray response, String url) {
// insert dummy data for demo
mBusinesses.clear();
Business business;
business = new Business();
business.setName("Google");
business.setDescription("Google HeadQuaters");
mBusinesses.add(business);
business = new Business();
business.setName("Yahoo");
business.setDescription("Yahoo HeadQuaters");
mBusinesses.add(business);
business = new Business();
business.setName("Microsoft");
business.setDescription("Microsoft HeadQuaters");
mBusinesses.add(business);
Log.d(Const.DEBUG, "Dummy Data Inserted\nBusinesses Length: "
+ mBusinesses.size());
mBusinessAdapter = new BusinessAdapter(mBusinesses);
mBusinessAdapter.notifyDataSetChanged();
}
My BusinessAdapter:
public class BusinessAdapter extends
RecyclerView.Adapter<BusinessAdapter.ViewHolder> {
private List<Business> mBusinesses = new ArrayList<Business>();
// Provide a reference to the type of views that you are using
// (custom viewholder)
public static class ViewHolder extends RecyclerView.ViewHolder {
public TextView mTextViewName;
public TextView mTextViewDescription;
public ImageView mImageViewLogo;
public ViewHolder(View v) {
super(v);
mTextViewName = (TextView) v
.findViewById(R.id.textView_company_name);
mTextViewDescription = (TextView) v
.findViewById(R.id.textView_company_description);
mImageViewLogo = (ImageView) v
.findViewById(R.id.imageView_company_logo);
}
}
// Provide a suitable constructor (depends on the kind of dataset)
public BusinessAdapter(List<Business> myBusinesses) {
Log.d(Const.DEBUG, "BusinessAdapter -> constructor");
mBusinesses = myBusinesses;
}
// Create new views (invoked by the layout manager)
#Override
public BusinessAdapter.ViewHolder onCreateViewHolder(ViewGroup parent,
int viewType) {
Log.d(Const.DEBUG, "BusinessAdapter -> onCreateViewHolder()");
// create a new view
View v = LayoutInflater.from(parent.getContext()).inflate(
R.layout.item_business_list, parent, false);
ViewHolder vh = new ViewHolder(v);
return vh;
}
// Replace the contents of a view (invoked by the layout manager)
#Override
public void onBindViewHolder(ViewHolder holder, int position) {
// - get element from your dataset at this position
// - replace the contents of the view with that element
Log.d(Const.DEBUG, "BusinessAdapter -> onBindViewHolder()");
Business item = mBusinesses.get(position);
holder.mTextViewName.setText(item.getName());
holder.mTextViewDescription.setText(item.getDescription());
holder.mImageViewLogo.setImageResource(R.drawable.ic_launcher);
}
// Return the size of your dataset (invoked by the layout manager)
#Override
public int getItemCount() {
Log.d(Const.DEBUG, "BusinessAdapter -> getItemCount()");
if (mBusinesses != null) {
Log.d(Const.DEBUG, "mBusinesses Count: " + mBusinesses.size());
return mBusinesses.size();
}
return 0;
}
}
But I don't get the data displayed in the view. What am I doing wrong?
Here is my log,
07-14 21:15:35.669: D/xxx(2259): Dummy Data Inserted
07-14 21:15:35.669: D/xxx(2259): Businesses Length: 3
07-14 21:26:26.969: D/xxx(2732): BusinessAdapter -> constructor
I don't get any logs after this. Shouldn't getItemCount() in adapter should be called again?

In your parseResponse() you are creating a new instance of the BusinessAdapter class, but you aren't actually using it anywhere, so your RecyclerView doesn't know the new instance exists.
You either need to:
Call recyclerView.setAdapter(mBusinessAdapter) again to update the RecyclerView's adapter reference to point to your new one
Or just remove mBusinessAdapter = new BusinessAdapter(mBusinesses); to continue using the existing adapter. Since you haven't changed the mBusinesses reference, the adapter will still use that array list and should update correctly when you call notifyDataSetChanged().

Try this method:
List<Business> mBusinesses2 = mBusinesses;
mBusinesses.clear();
mBusinesses.addAll(mBusinesses2);
//and do the notification
a little time consuming, but it should work.

Just to complement the other answers as I don't think anyone mentioned this here: notifyDataSetChanged() should be executed on the main thread (other notify<Something> methods of RecyclerView.Adapter as well, of course)
From what I gather, since you have the parsing procedures and the call to notifyDataSetChanged() in the same block, either you're calling it from a worker thread, or you're doing JSON parsing on main thread (which is also a no-no as I'm sure you know). So the proper way would be:
protected void parseResponse(JSONArray response, String url) {
// insert dummy data for demo
// <yadda yadda yadda>
mBusinessAdapter = new BusinessAdapter(mBusinesses);
// or just use recyclerView.post() or [Fragment]getView().post()
// instead, but make sure views haven't been destroyed while you were
// parsing
new Handler(Looper.getMainLooper()).post(new Runnable() {
public void run() {
mBusinessAdapter.notifyDataSetChanged();
}
});
}
PS Weird thing is, I don't think you get any indications about the main thread thing from either IDE or run-time logs. This is just from my personal observations: if I do call notifyDataSetChanged() from a worker thread, I don't get the obligatory Only the original thread that created a view hierarchy can touch its views message or anything like that - it just fails silently (and in my case one off-main-thread call can even prevent succeeding main-thread calls from functioning properly, probably because of some kind of race condition)
Moreover, neither the RecyclerView.Adapter api reference nor the relevant official dev guide explicitly mention the main thread requirement at the moment (the moment is 2017) and none of the Android Studio lint inspection rules seem to concern this issue either.
But, here is an explanation of this by the author himself

I had same problem. I just solved it with declaring adapter public before onCreate of class.
PostAdapter postAdapter;
after that
postAdapter = new PostAdapter(getActivity(), posts);
recList.setAdapter(postAdapter);
at last I have called:
#Override
protected void onPostExecute(Void aVoid) {
super.onPostExecute(aVoid);
// Display the size of your ArrayList
Log.i("TAG", "Size : " + posts.size());
progressBar.setVisibility(View.GONE);
postAdapter.notifyDataSetChanged();
}
May this will helps you.

Although it is a bit strange, but the notifyDataSetChanged does not really work without setting new values to adapter. So, you should do:
array = getNewItems();
((MyAdapter) mAdapter).setValues(array); // pass the new list to adapter !!!
mAdapter.notifyDataSetChanged();
This has worked for me.

Clear your old viewmodel and set the new data to the adapter and call notifyDataSetChanged()

In my case, force run #notifyDataSetChanged in main ui thread will fix
public void refresh() {
clearSelection();
// notifyDataSetChanged must run in main ui thread, if run in not ui thread, it will not update until manually scroll recyclerview
((Activity) ctx).runOnUiThread(new Runnable() {
#Override
public void run() {
adapter.notifyDataSetChanged();
}
});
}

I always have this problem that I forget that the RecyclerView expects a new instance of a List each time you feed the adapter.
List<X> deReferenced = new ArrayList(myList);
adapter.submitList(deReferenced);
Having the "same" List (reference) means not declaring "new" even if the List size changes, because the changes performed to the List also propagates to other Lists (when they are simply declared as this.localOtherList = myList) emphasis on the keyword being "=", usually components that compare collections make a copy of the result after the fact and store it as "old", but not Android DiffUtil.
So, if a component of yours is giving the same List each and every time you submit it, the RecyclerView won't trigger a new layout pass.
The reason is that... AFAIR, before the DiffUtil even attempts to apply the Mayers algorithm, there is a line doing a:
if (newList == mList)) {return;}
I am not sure how much "good practice" does de-referencing within the same system is actually defined as "good" ...
Specially since a diff algorithm is expected to have a new(revised) vs old(original) component which SHOULD in theory dereference the collection by itself after the process has ended but... who knows...?
But wait, there is more...
doing new ArrayList() dereferences the List, BUT for some reason Oracle decided that they should make a second "ArrayList" with the same name but a different functionality.
This ArrayList is within the Arrays class.
/**
* Returns a fixed-size list backed by the specified array. (Changes to
* the returned list "write through" to the array.) This method acts
* as bridge between array-based and collection-based APIs, in
* combination with {#link Collection#toArray}. The returned list is
* serializable and implements {#link RandomAccess}.
*
* <p>This method also provides a convenient way to create a fixed-size
* list initialized to contain several elements:
* <pre>
* List<String> stooges = Arrays.asList("Larry", "Moe", "Curly");
* </pre>
*
* #param <T> the class of the objects in the array
* #param a the array by which the list will be backed
* #return a list view of the specified array
*/
#SafeVarargs
#SuppressWarnings("varargs")
public static <T> List<T> asList(T... a) {
return new ArrayList<>(a); //Here
}
This write-through is funny because if you:
Integer[] localInts = new Integer[]{1, 2, 8};
Consumer<List<Integer>> intObserver;
public void getInts(Consumer<List<Integer>> intObserver) {
this.intObserver = intObserver;
dispatch();
}
private void dispatch() {
List<Integer> myIntegers = Arrays.asList(localInts);
intObserver.accept(myIntegers);
}
... later:
getInts(
myInts -> {
adapter.submitList(myInts); //myInts = [1, 2, 8]
}
);
Not only does the List dispatched obeys the dereferencing on each submission, but when the localInts variable is altered,
public void set(int index, Integer value) {
localInts[index] = value;
dispatch(); // dispatch again
}
...
myModel.set(1, 4) // localInts = [1, 4, 8]
this alteration is also passed to the List WITHIN the RecyclerView, this means that on the next submission, the (newList == mList) will return "false" allowing the DiffUtils to trigger the Mayers algorithm, BUT the areContentsTheSame(#NonNull T oldItem, #NonNull T newItem) callback from the ItemCallback<T> interface will throw a "true" when reaching index 1. basically, saying "the index 1 inside RecyclerView (that was supposed to be 2 in th previous version) was always 4", and a layout pass will still not perform.
So, the way to go in this case is:
List<Integer> trulyDereferenced = new ArrayList<>(Arrays.asList(localInts));
adapter.submitList(trulyDereferenced);