Develop Reference

Check if child view of RecyclerView item is visible on screen

I have a scenario in which I need to know if a child view of a RecyclerView item is visible on screen.
In this case, each RecyclerView item has a TextView and I need to know if that TextView is fully visible on screen. I've already figured this part out, but now my question is this:
How can I make a call to the adapter from my fragment to let it know that the view is visible on screen? What best practice should I follow for this?
Here is my fragment class method where I get the visible child view:
private void getFirstVisibleChildView() {
int findFirstVisibleItemPosition = layoutManager.findFirstVisibleItemPosition();
int findLastVisibleItemPosition = layoutManager.findLastVisibleItemPosition();
int [] positions = { findFirstVisibleItemPosition, findLastVisibleItemPosition };
PostAdapter.PostViewHolder viewHolder;
Rect scrollBounds = new Rect();
recyclerView.getDrawingRect(scrollBounds);
int[] location = new int[2];
for (int position : positions) {
RecyclerView.ViewHolder item = recyclerView.findViewHolderForAdapterPosition(position);
if (item instanceof PostAdapter.PostViewHolder) {
viewHolder = (PostAdapter.PostViewHolder) item;
viewHolder.getChildView().getLocationInWindow(location);
if (location[1] < 0 || location[1] > scrollBounds.bottom) {
// Not visible
} else {
// Visible
// How to call the RecyclerView adapter here and be able to manipulate it?
// Custom listener, direct call to ViewHolder, or some other method?
}
}
}
}
Thanks!

You can set addOnScrollListener on the RecyclerView, so it checkes if your specific view is fully shown whenever it's scrolled
And normally create a custom method in your adapter that you want to call within this listener when the above condition is met.
mRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
#Override
public void onScrolled(#NonNull RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
if (mRecyclerViewTafsir.getLayoutManager() == null) return;
// Here you can check if the particular textView is fully
// appeared on the screen >> You already did this part
mAdapter.callBack(); // call a method in the adapter when the condition is met
}
});

How to tell RecyclerView to start at specific item position

I want my RecyclerView with LinearLayoutManager to show up with scroll position at specific item after adapter got updated. (not first/last position)
Means the at first (re-)layout, this given position should be in visible area.
It should not layout with position 0 on top and scroll afterwards to target position.
My Adapter starts with itemCount=0, loads its data in thread and notifies its real count later. But the start position must be set already while count is still 0!
As of now I used some kind of post Runnable containingscrollToPosition but this has side effects (starts at first pos and jumps immediately to target position (0 -> target) and seems not to work well with DiffUtil (0 -> target -> 0))
Edit: To clearify: I need alternative to layoutManager.setStackFromEnd(true);, something like setStackFrom(position). ScrollToPosition does not work, if I call it when itemCount is still 0, so it gets ignored. If I call it when I notify that itemCount is now >0, it will layout from 0 and jumps short after to target position. And it fails completely if I use DiffUtil.DiffResult.dispatchUpdatesTo(adapter)`. (shows from 0, then scrolls to target position and then again back to position 0)

I found a solution myself:
I extended the LayoutManager:
class MyLayoutManager extends LinearLayoutManager {
private int mPendingTargetPos = -1;
private int mPendingPosOffset = -1;
#Override
public void onLayoutChildren(Recycler recycler, State state) {
if (mPendingTargetPos != -1 && state.getItemCount() > 0) {
/*
Data is present now, we can set the real scroll position
*/
scrollToPositionWithOffset(mPendingTargetPos, mPendingPosOffset);
mPendingTargetPos = -1;
mPendingPosOffset = -1;
}
super.onLayoutChildren(recycler, state);
}
#Override
public void onRestoreInstanceState(Parcelable state) {
/*
May be needed depending on your implementation.
Ignore target start position if InstanceState is available (page existed before already, keep position that user scrolled to)
*/
mPendingTargetPos = -1;
mPendingPosOffset = -1;
super.onRestoreInstanceState(state);
}
/**
* Sets a start position that will be used <b>as soon as data is available</b>.
* May be used if your Adapter starts with itemCount=0 (async data loading) but you need to
* set the start position already at this time. As soon as itemCount > 0,
* it will set the scrollPosition, so that given itemPosition is visible.
* #param position
* #param offset
*/
public void setTargetStartPos(int position, int offset) {
mPendingTargetPos = position;
mPendingPosOffset = offset;
}
}
It stores my target position. If onLayoutChildren is called by RecyclerView, it checks if adapters itemCount is already > 0. If true, it calls scrollToPositionWithOffset().
So I can tell immediately what position should be visible, but it will not be told to LayoutManager before position exists in Adapter.

You can try this, it will scroll to a position you want:
rv.getLayoutManager().scrollToPosition(positionInTheAdapter).

If you want to scroll to a specific position and that position is the adapter's position, then you can use StaggeredGridLayoutManager scrollToPosition
StaggeredGridLayoutManager staggeredGridLayoutManager = new StaggeredGridLayoutManager(1, StaggeredGridLayoutManager.VERTICAL);
staggeredGridLayoutManager.scrollToPosition(10);
recyclerView.setLayoutManager(staggeredGridLayoutManager);
If I understand the question, you want to scroll to a specific position but that position is the adapter's position and not the RecyclerView's item position.
You can only achieve this through the LayoutManager.
rv.getLayoutManager().scrollToPosition(youPositionInTheAdapter);

None of the methods above worked for me. I did the following using ViewTreeObserver that is triggered once its children have been added/changed visibility.
recyclerView.apply {
adapter = ...
layoutManager = ...
val itemCount = adapter?.itemCount ?: 0
if(itemCount > 1) {
viewTreeObserver.addOnGlobalLayoutListener(object: ViewTreeObserver.OnGlobalLayoutListener {
override fun onGlobalLayout() {
viewTreeObserver.removeOnGlobalLayoutListener(this)
(layoutManager as? LinearLayoutManager)?.scrollToPosition(#PositionToStartAt)
}
}
}
Go ahead and set #PositionToStartAt to a specific value. You can also ensure that the RecyclerView initial position setting gets triggered once a specific number of children have been laid out to ensure it is set correctly.
if(recyclerView.childCount() > #PositionCheck) {
viewTreeObserver.removeOnGlobalLayoutListener(this)
(layoutManager as? LinearLayoutManager)?.scrollToPosition(#PositionToStartAt)
}

If your only motive is to start the recyclerView from a specific position without any scroll-like animation I'll suggest using StaggeredGridLayoutManager
val staggeredGridLayoutManager = StaggeredGridLayoutManager(1, StaggeredGridLayoutManager.HORIZONTAL)//or VERTICAL
staggeredGridLayoutManager.scrollToPosition(specificPosition)
recyclerView.apply{
layoutManager = staggeredGridLayoutManager
}

Another contribution to a long running question...
As mentioned, layoutManager.scrollToPosition/WithOffset() does work to get the RecyclerView positioned, but timing this can be tricky. For example with variable length item views the RecyclerView has to work hard to get all the prior item views measured.
The approach below simply delays telling the RecyclerView about the prior items, then calls notifyItemRangeInserted(0, offset). This enabled the view to appear in the right place, with no visible scrolling at the start, and ready to scroll back.
private List<Bitmap> bitmaps = new ArrayList<>();
...
private class ViewAdapter extends RecyclerView.Adapter<ViewHolder> {
private volatile int offset;
private boolean offsetCancelled;
ViewAdapter(int initialOffset) {
this.offset = initialOffset;
this.offsetCancelled = initialOffset > 0;
}
#Override
public int getItemCount() {
return bitmaps.size() - offset;
}
#NonNull
#Override
public ViewHolder onCreateViewHolder(#NonNull ViewGroup parent, int viewType) {
ImageView imageView = new ImageView(MyActivity.this); // Or getContext() from a Fragment
RecyclerView.LayoutParams lp = new RecyclerView.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.WRAP_CONTENT);
imageView.setLayoutParams(lp);
return new ViewHolder(imageView);
}
#Override
public void onBindViewHolder(#NonNull ViewHolder holder, int position) {
holder.imageView.setImageBitmap(bitmaps.get(position + offset));
if (!offsetCancelled) {
offsetCancelled = true;
recyclerView.post(() -> {
int previousOffset = offset;
offset = 0;
notifyItemRangeInserted(0, previousOffset);
Log.i(TAG, "notifyItemRangeInserted(0, " + previousOffset + ")");
});
}
}
}
private class ViewHolder extends RecyclerView.ViewHolder {
private final ImageView imageView;
ViewHolder(#NonNull ImageView itemView) {
super(itemView);
this.imageView = itemView;
}
}
For context, this is a full example, based around ImageView's and Bitmap's. The key bit is the use of the offset in getItemCount() and onBindViewHolder().

Android - Detect when the last item in a RecyclerView is visible

I have a method that will check if the last element in a RecyclerView is completely visible by the user, so far I have this code
The problem is how to check if the RecyclerView has reached it's bottom ?
PS I have items dividers
public void scroll_btn_visibility_controller(){
if(/**last item is visible to user*/){
//This is the Bottom of the RecyclerView
Scroll_Top_Btn.setVisibility(View.VISIBLE);
}
else(/**last item is not visible to user*/){
Scroll_Top_Btn.setVisibility(View.INVISIBLE);
}
}
UPDATE : This is one of the attempts I tried
boolean isLastVisible() {
LinearLayoutManager layoutManager = ((LinearLayoutManager)rv.getLayoutManager());
int pos = layoutManager.findLastCompletelyVisibleItemPosition();
int numItems = disp_adapter.getItemCount();
return (pos >= numItems);
}
public void scroll_btn_visibility_controller(){
if(isLastVisible()){
Scroll_Top.setVisibility(View.VISIBLE);
}
else{
Scroll_Top.setVisibility(View.INVISIBLE);
}
}
so far no success I think there is something wrong within these lines :
int pos = layoutManager.findLastCompletelyVisibleItemPosition();
int numItems = disp_adapter.getItemCount();

You can create a callback in your adapter which will send a message to your activity/fragment every time when the last item is visible.
For example, you can implement this idea in onBindViewHolder method
#Override
public void onBindViewHolder(RecyclerView.ViewHolder viewHolder, int position) {
if(position==(getItemCount()-1)){
// here goes some code
// callback.sendMessage(Message);
}
//do the rest of your stuff
}
UPDATE
Well, I know it's been a while but today I ran into the same problem, and I came up with a solution that works perfectly. So, I'll just leave it here if anybody ever needs it:
recyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
#Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
LinearLayoutManager layoutManager=LinearLayoutManager.class.cast(recyclerView.getLayoutManager());
int totalItemCount = layoutManager.getItemCount();
int lastVisible = layoutManager.findLastVisibleItemPosition();
boolean endHasBeenReached = lastVisible + 5 >= totalItemCount;
if (totalItemCount > 0 && endHasBeenReached) {
//you have reached to the bottom of your recycler view
}
}
});

You should use your code with following change:
boolean isLastVisible() {
LinearLayoutManager layoutManager =((LinearLayoutManager) rv.getLayoutManager());
int pos = layoutManager.findLastCompletelyVisibleItemPosition();
int numItems = rv.getAdapter().getItemCount();
return (pos >= numItems - 1);
}
Be careful, findLastCompletelyVisibleItemPosition() returns the position which start at 0. So, you should minus 1 after numItems.

Assuming you're using LinearLayoutManager, this method should do the trick:
boolean isLastVisible() {
LinearLayoutManager layoutManager = ((LinearLayoutManager)mRecyclerView.getLayoutManager());
int pos = layoutManager.findLastCompletelyVisibleItemPosition();
int numItems = mRecyclerView.getAdapter().getItemCount();
return (pos >= numItems);
}

try working with onScrollStateChanged it will solve your issue

Try this solution as it depends on how you want to implement the chat.
In your onCreate() method add the call to post to your recyclerview and implement the runable method, this to guarantee that the element has already been loaded and then execute the scrollToPosition method adding the last element of your list as a parameter.
recyclerView.post(new Runnable() {
#Override
public void run() {
recyclerView.scrollToPosition(yourList().size()-1);
}
});

RecyclerView smooth scroll

I'm tring to make smooth scroller to need position in recyclerView. I'm ovverride method smoothScrollToPosition in LinearLayoutManager, and it's work fine. But, I need to set scrolled position on top of screen(if is possible). I also tried scrollToPositionWithOffset, and it's make that I need, but now, without smooth effect. How to mix this methods, and make smooth scroll with set item on top?
private LinearLayoutManager linearLayoutManager = new LinearLayoutManager(this){
#Override
public void smoothScrollToPosition(RecyclerView recyclerView,
RecyclerView.State state, final int position) {
LinearSmoothScroller smoothScroller =
new LinearSmoothScroller(getApplicationContext()) {
//This controls the direction in which smoothScroll looks
//for your view
#Override
public PointF computeScrollVectorForPosition
(int targetPosition) {
return this
.computeScrollVectorForPosition(targetPosition);
}
//This returns the milliseconds it takes to
//scroll one pixel.
#Override
protected float calculateSpeedPerPixel
(DisplayMetrics displayMetrics) {
return 50f/displayMetrics.densityDpi;
}
};
smoothScroller.setTargetPosition(position);
startSmoothScroll(smoothScroller);
}
};

This is late response, but I want to suggest a library SnappySmoothScroller.
This library enables smooth scroll with specific snap position: SnapType.START , SnapType.CENTER or SnapType.END
Use like this:
private LinearLayoutManager linearLayoutManager = new LinearLayoutManager(this) {
#Override
public void smoothScrollToPosition(RecyclerView recyclerView, RecyclerView.State state, int position) {
SnappySmoothScroller scroller = new SnappySmoothScroller.Builder()
.setPosition(position)
.setSnapType(SnapType.START)
.setScrollVectorDetector(new LinearLayoutScrollVectorDetector(this))
.build(recyclerView.getContext());
startSmoothScroll(scroller);
}
};

(Smooth)ScrollToPosition doesn't work properly with RecyclerView

I'm using basic RecyclerView with GridLayoutManager. I observed that nor smoothScrollToPosition nor scrollToPosition works properly.
a) when using smoothScrollToPosition I often receive error from RecyclerView
"RecyclerView﹕ Passed over target position while smooth scrolling."
and RecyclerView is not scrolled properly (often it misses the targeted row). This is observed mostly when I'm trying to scroll to the 1st item of some row
b) when using scrollToPosition it seems to work quite ok but most of the time I can see only the 1st item of the row and the rest are not displayed.
Can you give me some hints how to make work properly at least one of the methods?
Thanks a lot!

Finally I was able to make it work! LinearLayoutManager.scrollToPositionWithOffset(int, int) did the trick.

I also have same issue, but managed to fix the issue by Customizing SmoothScroller
let Custom LayoutManager as below
public class CustomLayoutManager extends LinearLayoutManager {
private static final float MILLISECONDS_PER_INCH = 50f;
private Context mContext;
public CustomLayoutManager(Context context) {
super(context);
mContext = context;
}
#Override
public void smoothScrollToPosition(RecyclerView recyclerView,
RecyclerView.State state, final int position) {
LinearSmoothScroller smoothScroller =
new LinearSmoothScroller(mContext) {
//This controls the direction in which smoothScroll looks
//for your view
#Override
public PointF computeScrollVectorForPosition
(int targetPosition) {
return CustomLayoutManager.this
.computeScrollVectorForPosition(targetPosition);
}
//This returns the milliseconds it takes to
//scroll one pixel.
#Override
protected float calculateSpeedPerPixel
(DisplayMetrics displayMetrics) {
return MILLISECONDS_PER_INCH/displayMetrics.densityDpi;
}
};
smoothScroller.setTargetPosition(position);
startSmoothScroll(smoothScroller);
}
}
(documentation commented inside the code given above)Please set the above LayoutManager
to the recyerview
CustomLayoutManagerlayoutManager = new CustomLayoutManager(getActivity());
recyclerView.setLayoutManager(layoutManager);
recyclerView.smoothScrollToPosition(position);
by using the custom Layout manager
scrollToPosition
also working well in my case u can use
recyclerView.scrollToPosition(position)
also if you want to adjust the speed of smoothScrollToPosition please override the
private static final float MILLISECONDS_PER_INCH = 50f;
in CustomLayoutManager.
So if we put the value as 1f the smoothScrollToPosition will be faster like scrollToPosition.increasing value make delay and decreasing will make the speed of scroll.
Hope this will useful.

In My case,
mRecyclerView.scrollToPosition(10);
also did not work.
But
mRecyclerView.smoothScrollToPosition(10);
works fine for me...

To scroll down smoothly to bottom from any position in the RecyclerView on clicking EditText.
edittext.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
rv_commentList.postDelayed(new Runnable() {
#Override
public void run() {
rv_commentList.scrollToPosition(rv_commentList.getAdapter().getItemCount() - 1);
}
}, 1000);
}
});

Another reason why any of the before mentioned solutions may not work is if your RecyclerView is embedded in a NestedScrollView. In this case you have to call the scroll action on the NestedScrollView.
for example:
nestedScrollview.smoothScrollTo(0,0)

This extension is so useful, try please.
fun RecyclerView.smoothSnapToPosition(position: Int, snapMode: Int = LinearSmoothScroller.SNAP_TO_START) {
val smoothScroller = object : LinearSmoothScroller(this.context) {
override fun getVerticalSnapPreference(): Int = snapMode
override fun getHorizontalSnapPreference(): Int = snapMode
}
smoothScroller.targetPosition = position
layoutManager?.startSmoothScroll(smoothScroller)
}

I was facing a weird issue wherein smoothScrollToPosition only worked occasionally.
After putting the smoothScrollToPosition inside Handler Post
Delayed with 1 second delay, it worked fine.
Refer to the following Kotlin example:
Handler().postDelayed({
recyclerViewObject.smoothScrollToPosition(0) // mention the position in place of 0
}, 1000) // 1000 indicates the 1 second delay.

recyclerView.getLayoutManager().smoothScrollToPosition(recyclerView,new RecyclerView.State(),currentPosition);

Try measuring item width or height and call smoothScrollBy(int dx, int dy).

How to perform smooth scrolling and save RecyclerView vertical position after device rotating:
This is the method that works for my case,
public class MainFragment extends Fragment { //OR activity it's //fragment in my case
....
#Override
public void onLoadFinished(#NonNull Loader<List<Report>> loader, List<Report> objects) { // or other method of your choice, in my case it's a Loader
RecyclerView recyclerViewRv = findViewById(........;
.....
recyclerViewRv.setAdapter(.....Your adapter);
recyclerViewRv.addOnScrollListener(new RecyclerView.OnScrollListener() {
#Override
public void onScrollStateChanged(#NonNull RecyclerView recyclerView, int newState) {
super.onScrollStateChanged(recyclerView, newState);
}
#Override
public void onScrolled(#NonNull RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
recyclerScrollY = recyclerViewRv. computeVerticalScrollOffset();
}
});
//Apply smooth vertical scroll
recyclerViewRv.smoothScrollBy(0,recyclerScrollY);
}
//Save vertical scroll position before rotating devices
#Override
public void onSaveInstanceState(#NonNull Bundle outState) {
super.onSaveInstanceState(outState);
outState.putInt("recyclerScrollY",recyclerScrollY);
}
//BackUp vertical scroll position after rotating devices
#Override
public void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if(savedInstanceState != null) {
recyclerScrollY = savedInstanceState.getInt("recyclerScrollY");
}
}
//If you want to perform the same operation for horizontal scrolling just add a variable called recyclerScrollX = recyclerScrollY = recyclerViewRv. computeHorizontalScrollOffset(); then save in bundle

Calling the recyclerView smoothScroll isn't effective, as the recyclerView itself doesn't handle its layout.
What you should do is calling the layout manager scroll method instead.
This should look something like this
mRecyclerView.getLayoutManager().scrollToPosition(desiredPosition);

If you are trying to do a quick scroll to a position at the top of the RecyclerView, just use LinearLayoutManager.scrollToPositionWithOffset with 0 as the offset.
Example:
mLinearLayoutManager = new LinearLayoutManager(this);
recyclerView.setLayoutManager(mLinearLayoutManager);
mLinearLayoutManager.scrollToPositionWithOffset(myPosition, 0);
smoothScrollToPosition is very slow. If you want something fast go with scrollToPositionWithOffset.

when you use scrollToPosition it will show it on top of the recycler view.
But if you use smoothScrollToPosition it will scroll till it come in to Window Visible. that's why while smoothScrool to item below, it will show it on bottom

Actually, if you have a RecyclerView inside a NestedScrollView, you must use both of these lines every time you want to go to the beginning of the RecyclerView:
nestedScrollView.smoothScrollTo(0, 0);
layoutManager.scrollToPositionWithOffset(0, 0);
This completely works for me.

this worked for me
Handler().postDelayed({
(recyclerView.getLayoutManager() as LinearLayoutManager).scrollToPositionWithOffset( 0, 0)
}, 100)

None of these answers worked for me. I needed to smoothScrollToPosition but #Ramz answer didn't work. I was finding it would consistently overscroll but only in one direction. I discovered that it seemed to be the item decorators throwing it off. I had a horizontal layout and I wanted to add a space after every item except the last and it didn't like that asymmetry. As soon as I included a space after every item, it worked!

nestedScroll.smoothScrollTo(0, recycler.top)

So i was looking for a solution to get back to the top with a recyclerview inside another layout that has a view on top of it (in my case I had a LinearLayout with a TextView and my recyclerview inside). Because of that the smoothscroll would go only to half the way to the first item.
Here's what I did which works really well (Kotlin solution):
back_to_top.setOnClickListener {
GlobalScope.launch(Dispatchers.Main) {
GlobalScope.launch(Dispatchers.Main) {
recyclerview.layoutManager?.smoothScrollToPosition(recyclerview, RecyclerView.State(), 0)
delay((recyclerview.layoutManager as LinearLayoutManager).findLastVisibleItemPosition() * 100L)
}.join()
recyclerview.scrollToPosition(0)
}
back_to_top.visibility = View.GONE
}
}
Here what I do is I smoothscroll to the first element and delay the scroll by 100ms times the last item visible and then call the scrollToPosition(0) (which goes to the top.correctly)