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Adding empty space between items of RecyclerView with GridLayoutManager

I want to add empty spaces between items of a RecyclerView with GridLayoutManager but I can't find anything which solves my problem.
I am creating a custom calendar and I have to make a custom grid from scratch. The first day of the month should be placed farther from the start when it is not the first day of the week.
I have achieved a similar result by passing a firstItemLocation to my RecyclerView adapter and overriding the onBindViewHolder method like this:
#Override
public void onBindViewHolder(#NonNull ViewHolder holder, int position) {
if (position < firstItemLocation) {
holder.itemView.setVisibility(View.GONE);
} else {
holder.tv.setText(String.format(Locale.US, "%d", list.get(position - firstItemLocation)));
}
}
It works fine but in a hypothetical situation when the user has to scroll it adds random empty spaces and glitches like this.
Any seggestions to make it better without that glitch?

read about "recycling pattern", how it works and why - RecyclerView got its name because of this, so its very important to understand how this works
but in short:
inside onBindViewHolder you have to call desired methods ALWAYS. you are calling setVisibility only inside if and not in else. try with bellow snippet
if (position < firstItemLocation) {
holder.itemView.setVisibility(View.GONE);
holder.tv.setText("")
} else {
holder.itemView.setVisibility(View.VISIBLE);
holder.tv.setText(String.format(Locale.US, "%d", list.get(position - firstItemLocation)));
}
thats because holder may be a "recycled" instance, used previously to draw another list item, and its set up is still applied to views

getChildAt(pos) returns null on RecyclerView

I am using RecyclerView where i have number of rows, each row has progress bar which updates.First four rows are visible.When row count is greater than 4 and i call getChildAt(pos) on my recyclerview to get the View,it is returning null. Kindly help.

As recyclerView.getChildAt(position) was giving me null in the above scenario, I finally solved using the lines below. It can be useful to people who run into similar scenarios.
RecyclerView.ViewHolder holder = (RecyclerView.ViewHolder)
recyclerView.findViewHolderForAdapterPosition(position);
if (null != holder) {
holder.itemView.findViewById(R.id.xyz).setVisibility(View.VISIBLE);
}

When there is more than one page of data in your recycler view and you're using getChildAt() method, it will throw a null pointer exception. This is because when the position is greater than the number of visible items on the display, getChildAt() won't work as it can only get to the view that is displayed on the screen.
Therefore, use recyclerView.layoutManager?.findViewByPosition(position) to get the view at the given position.

You can set tags for every item in your adapter:
#Override
public void onBindViewHolder(ViewHolder holder, int position) {
super.onBindViewHolder(holder,position);
holder.yourView.setTag(yourTag);
}
Then you can use the following code in your activity:
RecyclerView recyclerView=(RecyclerView)(findViewById(R.id.recycler));
View yourView=(View)(recyclerView.findViewWithTag(YourTag));

onBindViewHolder() is never called on view at position even though RecyclerView.findViewHolderForAdapterPosition() returns null at that position

I have a list with 13 items (although items may be added or removed), positions 0-12. When the fragment containing the RecyclerView is first shown, only positions 0 through 7 are visible to the user (position 7 being only half visible). In my adapter I Log every time a view holder is binded/bound (idk if grammar applies here) and record its position.
Adapter
#Override
public void onBindViewHolder(final ViewHolder holder, final int position) {
Log.d(TAG, "onBindViewHolder() position: " + position);
...
}
From my Log I see that positions 0-7 are bound:
I have a selectAll() method that gets each ViewHolder by adapter position. If the returned holder is NOT null I use the returned holder to update the view to show it's selected. If the returned holder IS null I call selectOnBind() a method that flags the view at that position update to show it's selected when it's binded rather than in real time since it's not currently shown:
public void selectAll() {
for (int i = 0; i < numberOfItemsInList; i++) {
MyAdapter.ViewHolder holder = (MyAdapter.ViewHolder)
mRecyclerView.findViewHolderForAdapterPosition(i);
Log.d(TAG, "holder at position " + i + " is " + holder);
if (holder != null) {
select(holder);
} else {
selectOnBind(i);
}
}
}
In this method I Log the holder along with its position:
So up to this point everything seems normal. We have positions 0-7 showing, and according to the Log these are the positions bound. When I hit selectAll() without changing the visible views (scrolling) I see that positions 0-7 are defined and 8-12 are null. So far so good.
Here's where it gets interesting. If after calling selectAll() I scroll further down the list positions 8 and 9 do not show they are selected.
When checking the Log I see that it's because they are never bound even though they were reported to be null:
Even more confusing is that this does not happen every time. If I first launch the app and test this it may work. But it seems to happen without fail afterwards. I'm guessing it has something to do with the views being recycled, but even so wouldn't they have to be bound?
EDIT (6-29-16)
After an AndroidStudio update I cannot seem to reproduce the bug. It works as I expected it to, binding the null views. If this problem should resurface, I will return to this post.

This is happening because:
The views are not added to the recyclerview (getChildAt will not work and will return null for that position)
They are cached also (onBind will not be called)
Calling recyclerView.setItemViewCacheSize(0) will fix this "problem".
Because the default value is 2 (private static final int DEFAULT_CACHE_SIZE = 2; in RecyclerView.Recycler), you'll always get 2 views that will not call onBind but that aren't added to the recycler

In your case views for positions 8 and 9 are not being recycled, they are being detached from the window and will be attached again. And for these detached view onBindViewHolder is not called, only onViewAttachedToWindow is called. If you override these function in your adapter, you can see what I am talking.
#Override
public void onViewRecycled(ViewHolder vh){
Log.wtf(TAG,"onViewRecycled "+vh);
}
#Override
public void onViewDetachedFromWindow(ViewHolder viewHolder){
Log.wtf(TAG,"onViewDetachedFromWindow "+viewHolder);
}
Now in order to solve your problem you need to keep track of the views which were supposed to recycled but get detached and then do your section process on
#Override
public void onViewAttachedToWindow(ViewHolder viewHolder){
Log.wtf(TAG,"onViewAttachedToWindow "+viewHolder);
}

The answers by Pedro Oliveira and Zartha are great for understanding the problem, but I don't see any solutions I'm happy with.
I believe you have 2 good options depending on what you're doing:
Option 1
If you want onBindViewHolder() to get called for an off-screen view regardless if it's cached/detached or not, then you can do:
RecyclerView.ViewHolder view_holder = recycler_view.findViewHolderForAdapterPosition( some_position );
if ( view_holder != null )
{
//manipulate the attached view
}
else //view is either non-existant or detached waiting to be reattached
notifyItemChanged( some_position );
The idea is that if the view is cached/detached, then notifyItemChanged() will tell the adapter that view is invalid, which will result in onBindViewHolder() getting called.
Option 2
If you only want to execute a partial change (and not everything inside onBindViewHolder()), then inside of onBindViewHolder( ViewHolder view_holder, int position ), you need to store the position in the view_holder, and execute the change you want in onViewAttachedToWindow( ViewHolder view_holder ).
I recommend option 1 for simplicity unless your onBindViewHolder() is doing something intensive like messing with Bitmaps.

When you have large number of items in the list you have passed to recyclerview adapter you will not encounter the issue of onBindViewHolder() not executing while scrolling.
But if the list has less items(I have checked on list size 5) you may encounter this issue.
Better solution is to check list size.
Please find sample code below.
private void setupAdapter(){
if (list.size() <= 10){
recycler.setItemViewCacheSize(0);
}
recycler.setAdapter(adapter);
recycler.setLayoutManager(linearLayoutManager);
}

I think playing with view is not a good idea in recyclerview. The approach I always use to follow to just introduce a flag to the model using for RecyclerView. Let assume your model is like -
class MyModel{
String name;
int age;
}
If you are tracking the view is selected or not then introduce one boolean to the model. Now it will look like -
class MyModel{
String name;
int age;
boolean isSelected;
}
Now your check box will be selected/un-selected on the basis of the new flag isSelected (in onBindViewHolder() ). On every selection on view will change the value of corresponding model selected value to true, and on unselected change it to false. In your case just run a loop to change all model's isSelected value to true and then call notifyDataSetChanged().
For Example, let assume your list is
ArrayList<MyModel> recyclerList;
private void selectAll(){
for(MyModel myModel:recyclerList)
myModel.isSelected = true;
notifyDataSetChanged();
}
My suggestion, while using recyclerView or ListView to less try to play with views.
So in your case -
#Override
public void onBindViewHolder(final ViewHolder holder, final int position) {
holder.clickableView.setTag(position);
holder.selectableView.setTag(position);
holder.checkedView.setChecked(recyclerList.get(position).isSelected);
Log.d(TAG, "onBindViewHolder() position: " + position);
...
}
#Override
public void onClick(View view){
int position = (int)view.getTag();
recyclerList.get(position).isSelected = !recyclerList.get(position).isSelected;
}
#Override
public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
int position = (int)buttonView.getTag();
recyclerList.get(position).isSelected = isChecked;
}
Hope it will help you, Please let me know if you need any further explanation :)

So I think you question is answered below by #Pedro Oliveira. The main sense of RecycleView, that he using special algorithms for caching ViewHolder in any time. So next onBindViewHolder(...) may not work, for ex. if view is static, or something else.
And about your question you think to use RecycleView for dynamic changed Views. DON'T DO IT! Because RecycleView invalidates views and has caching system, so you will have a lot of problems.
Use LinkedListView for this task!

Refreshing data in RecyclerView and keeping its scroll position

How does one refresh the data displayed in RecyclerView (calling notifyDataSetChanged on its adapter) and make sure that the scroll position is reset to exactly where it was?
In case of good ol' ListView all it takes is retrieving getChildAt(0), checking its getTop() and calling setSelectionFromTop with the same exact data afterwards.
It doesn't seem to be possible in case of RecyclerView.
I guess I'm supposed to use its LayoutManager which indeed provides scrollToPositionWithOffset(int position, int offset), but what's the proper way to retrieve the position and the offset?
layoutManager.findFirstVisibleItemPosition() and layoutManager.getChildAt(0).getTop()?
Or is there a more elegant way to get the job done?

I use this one.^_^
// Save state
private Parcelable recyclerViewState;
recyclerViewState = recyclerView.getLayoutManager().onSaveInstanceState();
// Restore state
recyclerView.getLayoutManager().onRestoreInstanceState(recyclerViewState);
It is simpler, hope it will help you!

I have quite similar problem. And I came up with following solution.
Using notifyDataSetChanged is a bad idea. You should be more specific, then RecyclerView will save scroll state for you.
For example, if you only need to refresh, or in other words, you want each view to be rebinded, just do this:
adapter.notifyItemRangeChanged(0, adapter.getItemCount());

EDIT: To restore the exact same apparent position, as in, make it look exactly like it did, we need to do something a bit different (See below how to restore the exact scrollY value):
Save the position and offset like this:
LinearLayoutManager manager = (LinearLayoutManager) mRecycler.getLayoutManager();
int firstItem = manager.findFirstVisibleItemPosition();
View firstItemView = manager.findViewByPosition(firstItem);
float topOffset = firstItemView.getTop();
outState.putInt(ARGS_SCROLL_POS, firstItem);
outState.putFloat(ARGS_SCROLL_OFFSET, topOffset);
And then restore the scroll like this:
LinearLayoutManager manager = (LinearLayoutManager) mRecycler.getLayoutManager();
manager.scrollToPositionWithOffset(mStatePos, (int) mStateOffset);
This restores the list to its exact apparent position. Apparent because it will look the same to the user, but it will not have the same scrollY value (because of possible differences in landscape/portrait layout dimensions).
Note that this only works with LinearLayoutManager.
--- Below how to restore the exact scrollY, which will likely make the list look different ---
Apply an OnScrollListener like so:
private int mScrollY;
private RecyclerView.OnScrollListener mTotalScrollListener = new RecyclerView.OnScrollListener() {
#Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
mScrollY += dy;
}
};
This will store the exact scroll position at all times in mScrollY.
Store this variable in your Bundle, and restore it in state restoration to a different variable, we'll call it mStateScrollY.
After state restoration and after your RecyclerView has reset all its data reset the scroll with this:
mRecyclerView.scrollBy(0, mStateScrollY);
That's it.
Beware, that you restore the scroll to a different variable, this is important, because the OnScrollListener will be called with .scrollBy() and subsequently will set mScrollY to the value stored in mStateScrollY. If you do not do this mScrollY will have double the scroll value (because the OnScrollListener works with deltas, not absolute scrolls).
State saving in activities can be achieved like this:
#Override
protected void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
outState.putInt(ARGS_SCROLL_Y, mScrollY);
}
And to restore call this in your onCreate():
if(savedState != null){
mStateScrollY = savedState.getInt(ARGS_SCROLL_Y, 0);
}
State saving in fragments works in a similar way, but the actual state saving needs a bit of extra work, but there are plenty of articles dealing with that, so you shouldn't have a problem finding out how, the principles of saving the scrollY and restoring it remain the same.

Keep scroll position by using #DawnYu answer to wrap notifyDataSetChanged() like this:
val recyclerViewState = recyclerView.layoutManager?.onSaveInstanceState()
adapter.notifyDataSetChanged()
recyclerView.layoutManager?.onRestoreInstanceState(recyclerViewState)

Yes you can resolve this issue by making the adapter constructor only one time, I am explaining the coding part here :
if (appointmentListAdapter == null) {
appointmentListAdapter = new AppointmentListAdapter(AppointmentsActivity.this);
appointmentListAdapter.addAppointmentListData(appointmentList);
appointmentListAdapter.setOnStatusChangeListener(onStatusChangeListener);
appointmentRecyclerView.setAdapter(appointmentListAdapter);
} else {
appointmentListAdapter.addAppointmentListData(appointmentList);
appointmentListAdapter.notifyDataSetChanged();
}
Now you can see I have checked the adapter is null or not and only initialize when it is null.
If adapter is not null then I am assured that I have initialized my adapter at least one time.
So I will just add list to adapter and call notifydatasetchanged.
RecyclerView always holds the last position scrolled, therefore you don't have to store last position, just call notifydatasetchanged, recycler view always refresh data without going to top.
Thanks
Happy Coding

The top answer by #DawnYu works, but the recyclerview will first scroll to the top, then go back to the intended scroll position causing a "flicker like" reaction which isn't pleasant.
To refresh the recyclerView, especially after coming from another activity, without flickering, and maintaining the scroll position, you need to do the following.
Ensure you are updating you recycler view using DiffUtil. Read more about that here: https://www.journaldev.com/20873/android-recyclerview-diffutil
Onresume of your activity, or at the point you want to update your activity, load data to your recyclerview. Using the diffUtil, only the updates will be made on the recyclerview while maintaining it position.
Hope this helps.

Here is an option for people who use DataBinding for RecyclerView.
I have var recyclerViewState: Parcelable? in my adapter. And I use a BindingAdapter with a variation of #DawnYu's answer to set and update data in the RecyclerView:
#BindingAdapter("items")
fun setRecyclerViewItems(
recyclerView: RecyclerView,
items: List<RecyclerViewItem>?
) {
var adapter = (recyclerView.adapter as? RecyclerViewAdapter)
if (adapter == null) {
adapter = RecyclerViewAdapter()
recyclerView.adapter = adapter
}
adapter.recyclerViewState = recyclerView.layoutManager?.onSaveInstanceState()
// the main idea is in this call with a lambda. It allows to avoid blinking on data update
adapter.submitList(items.orEmpty()) {
adapter.recyclerViewState?.let {
recyclerView.layoutManager?.onRestoreInstanceState(it)
}
}
}
Finally, the XML part looks like:
<androidx.recyclerview.widget.RecyclerView
android:id="#+id/possible_trips_rv"
android:layout_width="match_parent"
android:layout_height="0dp"
app:items="#{viewState.yourItems}"
app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"/>

I was making a mistake like this, maybe it will help someone :)
If you use recyclerView.setAdapter every time new data come, it calls the adapter clear() method every time you use it, which causes the recyclerview to refresh and start over. To get rid of this, you need to use adapter.notiftyDatasetChanced().

1- You need to save scroll position like this
rvProduct.addOnScrollListener(new RecyclerView.OnScrollListener() {
#Override
public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
super.onScrollStateChanged(recyclerView, newState);
recyclerViewState = rvProduct.getLayoutManager().onSaveInstanceState(); // save recycleView state
}
});
2- And after you call notifyDataSetChanged then onRestoreInstanceState like this example
productsByBrandAdapter.addData(productCompareList);
productsByBrandAdapter.notifyDataSetChanged();
rvProduct.getLayoutManager().onRestoreInstanceState(recyclerViewState); // restore recycleView state

I have not used Recyclerview but I did it on ListView. Sample code in Recyclerview:
setOnScrollListener(new RecyclerView.OnScrollListener() {
#Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
rowPos = mLayoutManager.findFirstVisibleItemPosition();
It is the listener when user is scrolling. The performance overhead is not significant. And the first visible position is accurate this way.

Create Extention and use it entirely your App, if you are using DiffUtil you don't need to add adapter.notifyDataSetChanged()
fun RecyclerView.reStoreState(){
val recyclerViewState = this.layoutManager?.onSaveInstanceState()
this.layoutManager?.onRestoreInstanceState(recyclerViewState)
}
Then use it like this below
yourRecyclerView.reStoreState()
adapter.submitList(yourData)
yourRecyclerView.adapter = adapter

#BindingAdapter("items")
fun <T> RecyclerView.setItems(items: List<T>?) {
(adapter as? ListAdapter<T, *>)?.submitList(items) {
layoutManager?.onSaveInstanceState().let {
layoutManager?.onRestoreInstanceState(it)
}
}
}

mMessageAdapter.registerAdapterDataObserver(new RecyclerView.AdapterDataObserver() {
#Override
public void onChanged() {
mLayoutManager.smoothScrollToPosition(mMessageRecycler, null, mMessageAdapter.getItemCount());
}
});
The solution here is to keep on scrolling recyclerview when new message comes.
The onChanged() method detects the action performed on recyclerview.

That's working for me in Kotlin.
Create the Adapter and hand over your data in the constructor
class LEDRecyclerAdapter (var currentPole: Pole): RecyclerView.Adapter<RecyclerView.ViewHolder>() { ... }
change this property and call notifyDataSetChanged()
adapter.currentPole = pole
adapter.notifyDataSetChanged()
The scroll offset doesn't change.

If you have one or more EditTexts inside of a recyclerview items, disable the autofocus of these, putting this configuration in the parent view of recyclerview:
android:focusable="true"
android:focusableInTouchMode="true"
I had this issue when I started another activity launched from a recyclerview item, when I came back and set an update of one field in one item with notifyItemChanged(position) the scroll of RV moves, and my conclusion was that, the autofocus of EditText Items, the code above solved my issue.
best.

Just return if the oldPosition and position is same;
private int oldPosition = -1;
public void notifyItemSetChanged(int position, boolean hasDownloaded) {
if (oldPosition == position) {
return;
}
oldPosition = position;
RLog.d(TAG, " notifyItemSetChanged :: " + position);
DBMessageModel m = mMessages.get(position);
m.setVideoHasDownloaded(hasDownloaded);
notifyItemChanged(position, m);
}

I had this problem with a list of items which each had a time in minutes until they were 'due' and needed updating. I'd update the data and then after, call
orderAdapter.notifyDataSetChanged();
and it'd scroll to the top every time. I replaced that with
for(int i = 0; i < orderArrayList.size(); i++){
orderAdapter.notifyItemChanged(i);
}
and it was fine. None of the other methods in this thread worked for me. In using this method though, it made each individual item flash when it was updated so I also had to put this in the parent fragment's onCreateView
RecyclerView.ItemAnimator animator = orderRecycler.getItemAnimator();
if (animator instanceof SimpleItemAnimator) {
((SimpleItemAnimator) animator).setSupportsChangeAnimations(false);
}

RecyclerView Adapter notifyDataSetChanged stops fancy animation

I am building a component based on RecyclerView, allowing user to reorder items by drag and drop.
Once I am on the DragListener side, I need the position it has in the adapter in order to perform correct move, but I only have access to the view.
So here is what I am doing in the adapter view binding :
#Override
public void onBindViewHolder(ViewHolder viewHolder, int position) {
Track track = mArray.get(position);
viewHolder.itemView.setTag(R.string.TAG_ITEM_POSITION, position);
}
Does it seem correct to you ?
Because if I move an item like this :
public void move(int from, int to){
Track track = mArray.remove(from);
mArray.add(to, track);
notifyItemMoved(from, to);
}
then position tag is not correct anymore, and if I notifyDataSetChanged(), I lose the fancy animation.
Any suggestion ?

There is a way to preserve fancy animations with just notifyDataSetChanged()
You need to make your own GridLayoutManager with overriden supportsPredictiveItemAnimations() method returning true;
You need to mAdapter.setHasStableIds(true)
The part I find tricky is you need to override you adapter's getItemId() method. It should return value that is truly unique and not a direct function of position. Something like mItems.get(position).hashCode()
Worked perfectly fine in my case - beautiful animations for adding, removing and moving items only using notifyDataSetChanged()

No, it is wrong. First of all, you cannot reference to the position passed to the onBindViewHolder after that method returns. RecyclerView will not rebind a view when its position changes (due to items moving etc).
Instead, you can use ViewHolder#getPosition() which will return you the updated position.
If you fix that, your move code should work & provide nice animations.
Calling notifyDataSetChanged will prevent predictive animations so avoid it as long as you can. See documentation for details.
Edit (from comment): to get position from the outside, get child view holder from recyclerview and then get position from the vh. See RecyclerView api for details

1) You'll use notifyItemInserted(position); or notifyItemRemoved(position); instead of notifyDataSetChanged() for animation.
2) You can just manually fix your problem - using
public void move(int from, int to){
Track track = mArray.remove(from);
mArray.add(to, track);
notifyItemMoved(from, to);
ViewHolder fromHolder = (ViewHolder) mRecyclerView.findViewHolderForPosition(from);
ViewHolder toHolder = (ViewHolder) mRecyclerView.findViewHolderForPosition(to);
Tag fromTag = fromHolder.itemView.getTag();
fromHolder.itemView.setTag(toHolder.itemView.getTag());
toHolder.itemView.setTag(fromTag);
}

You should move your method to OnCreateViewHolder, then notifyItemRemoved(index) works properly.

I'm able to maintain the touch animations by adding this to my list item's outer element
<View
android:foreground="?android:attr/selectableItemBackground"
...>

I fixed it with using 'notifyItemChanged(int position);' instead of 'notifyDataSetChanged();'
My adapter shows fancy animations perfectly and without any lags
Edit: I got position from onBindViewHolder's position.

as stated by others above, you can have animation while using notifyDataSetChanged on your adapter, although you need to specifically use stable ids. if your items IDs are strings, you can generate a long id for each string id you have and keep them in a map. for example:
class StringToLongIdMap {
private var stringToLongMap = HashMap<String, Long>()
private var longId: Long = 0
fun getLongId(stringId: String): Long {
if (!stringToLongMap.containsKey(stringId)) {
stringToLongMap[stringId] = longId++
}
return stringToLongMap[stringId] ?: -1
}
}
and then in your adapter:
private var stringToLongIdMap = StringToLongIdMap()
override fun getItemId(position: Int): Long {
val item = items[position]
return stringToLongIdMap.getLongId(item.id)
}
another useful thing to consider, if you are using kotlin data class as items in your adapter, and you don't have an id, you can use the hashCode of the data class itself as stable id (if you are sure that the item properties combination are unique in your data set):
override fun getItemId(position: Int): Long = items[position].hashCode().toLong()