Related
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
}
});
I need to know which elements are currently displayed in my RecyclerView. There is no equivalent to the OnScrollListener.onScroll(...) method on ListViews. I tried to work with View.getGlobalVisibleRect(...), but that hack is too ugly and does not always work too.
Someone any ideas?
First / last visible child depends on the LayoutManager.
If you are using LinearLayoutManager or GridLayoutManager, you can use
int findFirstVisibleItemPosition();
int findFirstCompletelyVisibleItemPosition();
int findLastVisibleItemPosition();
int findLastCompletelyVisibleItemPosition();
For example:
GridLayoutManager layoutManager = ((GridLayoutManager)mRecyclerView.getLayoutManager());
int firstVisiblePosition = layoutManager.findFirstVisibleItemPosition();
For LinearLayoutManager, first/last depends on the adapter ordering. Don't query children from RecyclerView; LayoutManager may prefer to layout more items than visible for caching.
For those who have a logic to be implemented inside the RecyclerView adapter, you can still use the #ernesto approach combined with an on scrollListener to get what you want as the RecyclerView is consulted.
Inside the adapter you will have something like this:
#Override
public void onAttachedToRecyclerView(#NonNull RecyclerView recyclerView) {
super.onAttachedToRecyclerView(recyclerView);
RecyclerView.LayoutManager manager = recyclerView.getLayoutManager();
if(manager instanceof LinearLayoutManager && getItemCount() > 0) {
LinearLayoutManager llm = (LinearLayoutManager) manager;
recyclerView.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);
int visiblePosition = llm.findFirstCompletelyVisibleItemPosition();
if(visiblePosition > -1) {
View v = llm.findViewByPosition(visiblePosition);
//do something
v.setBackgroundColor(Color.parseColor("#777777"));
}
}
});
}
}
Finally, I found a solution to know if the current item is visible, from the onBindViewHolder event in the adapter.
The key is the method isViewPartiallyVisible from LayoutManager.
In your adapter, you can get the LayoutManager from the RecyclerView, which you get as parameter from the onAttachedToRecyclerView event.
You can use recyclerView.getChildAt() to get each visible child, and setting some tag convertview.setTag(index) on these view in adapter code will help you to relate it with adapter data.
Addendum:
The proposed functions findLast...Position() do not work correctly in a scenario with a collapsing toolbar while the toolbar is expanded.
It seems that the recycler view has a fixed height, and while the toolbar is expanded, the recycler is moved down, partially out of the screen. As a consequence the results of the proposed functions are too high. Example: The last visible item is told to be #9, but in fact item #7 is the last one that is on screen.
This behaviour is also the reason why my view often failed to scroll to the correct position, i.e. scrollToPosition() did not work correctly (I finally collapsed the toolbar programmatically).
Every answer above is correct and I would like to add also a snapshot from my working codes.
recycler.addOnScrollListener(new RecyclerView.OnScrollListener() {
#Override
public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
super.onScrollStateChanged(recyclerView, newState);
// Some code when initially scrollState changes
}
#Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
// Some code while the list is scrolling
LinearLayoutManager lManager = (LinearLayoutManager) recyclerView.getLayoutManager();
int firstElementPosition = lManager.findFirstVisibleItemPosition();
}
});
Following Linear / Grid LayoutManager methods can be used to check which items are visible.
int findFirstVisibleItemPosition();
int findLastVisibleItemPosition();
int findFirstCompletelyVisibleItemPosition();
int findLastCompletelyVisibleItemPosition();
and if you want to track is item visible on screen for some threshold then you can refer to the following blog.
https://proandroiddev.com/detecting-list-items-perceived-by-user-8f164dfb1d05
For StaggeredGridLayoutManager do this:
RecyclerView rv = findViewById(...);
StaggeredGridLayoutManager lm = new StaggeredGridLayoutManager(...);
rv.setLayoutManager(lm);
And to get visible item views:
int[] viewsIds = lm.findFirstCompletelyVisibleItemPositions(null);
ViewHolder firstViewHolder = rvPlantios.findViewHolderForLayoutPosition(viewsIds[0]);
View itemView = viewHolder.itemView;
Remember to check if it is empty.
You can find the first and last visible children of the recycle view and check if the view you're looking for is in the range:
var visibleChild: View = rv.getChildAt(0)
val firstChild: Int = rv.getChildAdapterPosition(visibleChild)
visibleChild = rv.getChildAt(rv.childCount - 1)
val lastChild: Int = rv.getChildAdapterPosition(visibleChild)
println("first visible child is: $firstChild")
println("last visible child is: $lastChild")
For those who are looking for an answer in Kotlin:
fun getVisibleItem(recyclerView : RecyclerView) {
recyclerView.addOnScrollListener(object: RecyclerView.OnScrollListener() {
override fun onScrollStateChanged(recyclerView: RecyclerView, newState: Int) {
if(newState == RecyclerView.SCROLL_STATE_IDLE) {
val index = (recyclerView.layoutManager.findFirstVisibleItemPosition
//use this index for any operation you want to perform on the item visible on screen. eg. log(arrayList[index])
}
}
})
}
You can explore other methods for getting the position as per your use case.
int findFirstCompletelyVisibleItemPosition()
int findLastVisibleItemPosition()
int findLastCompletelyVisibleItemPosition()
if the visible item position is different from the item position toast message will show on the screen.
myRecyclerview.addOnScrollListener(new RecyclerView.OnScrollListener() {
#Override
public void onScrollStateChanged(#NonNull RecyclerView recyclerView, int newState) {
super.onScrollStateChanged(recyclerView, newState);
LinearLayoutManager manager= (LinearLayoutManager) myRecyclerview.getLayoutManager();
assert manager != null;
int visiblePosition = manager.findLastCompletelyVisibleItemPosition();
if(visiblePosition > -1&&a!=visiblePosition) {
Toast.makeText(context,String.valueOf(visiblePosition),Toast.LENGTH_SHORT).show();
//do something
a=visiblePosition;
}
}
#Override
public void onScrolled(#NonNull RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
//Some code while the list is scrolling
}
});
I'm looking for a way to scroll a RecyclerView to show the selected item on top.
In a ListView I was able to do that by using scrollTo(x,y) and getting the top of the element that need to be centered.
Something like:
#Override
public void onItemClick(View v, int pos){
mylistView.scrollTo(0, v.getTop());
}
The problem is that the RecyclerView returns an error when using it's scrollTo method saying
RecyclerView does not support scrolling to an absolute position
How can I scroll a RecyclerView to put the selected item at the top of the view?
If you are using the LinearLayoutManager or Staggered GridLayoutManager, they each have a scrollToPositionWithOffset method that takes both the position and also the offset of the start of the item from the start of the RecyclerView, which seems like it would accomplish what you need (setting the offset to 0 should align with the top).
For instance:
//Scroll item 2 to 20 pixels from the top
linearLayoutManager.scrollToPositionWithOffset(2, 20);
If you looking for vertical LinearLayout Manager you can achieve smooth scrolling using a custom LinearSmoothScroller:
import android.content.Context;
import android.graphics.PointF;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.LinearSmoothScroller;
import android.support.v7.widget.RecyclerView;
public class SnappingLinearLayoutManager extends LinearLayoutManager {
public SnappingLinearLayoutManager(Context context, int orientation, boolean reverseLayout) {
super(context, orientation, reverseLayout);
}
#Override
public void smoothScrollToPosition(RecyclerView recyclerView, RecyclerView.State state,
int position) {
RecyclerView.SmoothScroller smoothScroller = new TopSnappedSmoothScroller(recyclerView.getContext());
smoothScroller.setTargetPosition(position);
startSmoothScroll(smoothScroller);
}
private class TopSnappedSmoothScroller extends LinearSmoothScroller {
public TopSnappedSmoothScroller(Context context) {
super(context);
}
#Override
public PointF computeScrollVectorForPosition(int targetPosition) {
return SnappingLinearLayoutManager.this
.computeScrollVectorForPosition(targetPosition);
}
#Override
protected int getVerticalSnapPreference() {
return SNAP_TO_START;
}
}
}
use an instance of the layoutmanager in recycle view and then calling recyclerView.smoothScrollToPosition(pos); will smooth scroll to selected position to top of the recycler view
//Scroll item pos
linearLayoutManager.scrollToPositionWithOffset(pos, 0);
You just need to call recyclerview.scrollToPosition(position). That's fine!
If you want to call it in adapter, just let your adapter has the instance of recyclerview or the activity or fragment which contains recyclerview,than implements the method getRecyclerview() in them.
I hope it can help you.
If you want to scroll automatic without show scroll motion then you need to write following code:
mRecyclerView.getLayoutManager().scrollToPosition(position);
If you want to display scroll motion then you need to add following code.
=>Step 1: You need to declare SmoothScroller.
RecyclerView.SmoothScroller smoothScroller = new
LinearSmoothScroller(this.getApplicationContext()) {
#Override
protected int getVerticalSnapPreference() {
return LinearSmoothScroller.SNAP_TO_START;
}
};
=>step 2: You need to add this code any event you want to perform scroll to specific position.
=>First you need to set target position to SmoothScroller.
smoothScroller.setTargetPosition(position);
=>Then you need to set SmoothScroller to LayoutManager.
mRecyclerView.getLayoutManager().startSmoothScroll(smoothScroller);
just call this method simply:
((LinearLayoutManager)recyclerView.getLayoutManager()).scrollToPositionWithOffset(yourItemPosition,0);
instead of:
recyclerView.scrollToPosition(yourItemPosition);
same with speed regulator
public class SmoothScrollLinearLayoutManager extends LinearLayoutManager {
private static final float MILLISECONDS_PER_INCH = 110f;
private Context mContext;
public SmoothScrollLinearLayoutManager(Context context,int orientation, boolean reverseLayout) {
super(context,orientation,reverseLayout);
mContext = context;
}
#Override
public void smoothScrollToPosition(RecyclerView recyclerView, RecyclerView.State state,
int position) {
RecyclerView.SmoothScroller smoothScroller = new TopSnappedSmoothScroller(recyclerView.getContext()){
//This controls the direction in which smoothScroll looks for your view
#Override
public PointF computeScrollVectorForPosition(int targetPosition) {
return new PointF(0, 1);
}
//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);
}
private class TopSnappedSmoothScroller extends LinearSmoothScroller {
public TopSnappedSmoothScroller(Context context) {
super(context);
}
#Override
public PointF computeScrollVectorForPosition(int targetPosition) {
return SmoothScrollLinearLayoutManager.this
.computeScrollVectorForPosition(targetPosition);
}
#Override
protected int getVerticalSnapPreference() {
return SNAP_TO_START;
}
}
}
Try what worked for me cool!
Create a variable private static int displayedposition = 0;
Now for the position of your RecyclerView in your Activity.
myRecyclerView.setOnScrollListener(new RecyclerView.OnScrollListener() {
#Override
public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
super.onScrollStateChanged(recyclerView, newState);
}
#Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
LinearLayoutManager llm = (LinearLayoutManager) myRecyclerView.getLayoutManager();
displayedposition = llm.findFirstVisibleItemPosition();
}
});
Place this statement where you want it to place the former site displayed in your view .
LinearLayoutManager llm = (LinearLayoutManager) mRecyclerView.getLayoutManager();
llm.scrollToPositionWithOffset(displayedposition , youList.size());
Well that's it , it worked fine for me \o/
what i did to restore the scroll position after refreshing the RecyclerView on button clicked:
if (linearLayoutManager != null) {
index = linearLayoutManager.findFirstVisibleItemPosition();
View v = linearLayoutManager.getChildAt(0);
top = (v == null) ? 0 : (v.getTop() - linearLayoutManager.getPaddingTop());
Log.d("TAG", "visible position " + " " + index);
}
else{
index = 0;
}
linearLayoutManager = new LinearLayoutManager(getApplicationContext());
linearLayoutManager.scrollToPositionWithOffset(index, top);
getting the offset of the first visible item from the top before creating the linearLayoutManager object and after instantiating it the scrollToPositionWithOffset of the LinearLayoutManager object was called.
I don't know why I didn't find the best answer but its really simple.
recyclerView.smoothScrollToPosition(position);
No errors
Creates Animations
What i may add here is how to make it work together with DiffUtil and ListAdapter
You may note that calling recyclerView.scrollToPosition(pos) or (recyclerView.layoutManager as LinearLayoutManager).scrollToPositionWithOffset(pos, offset) wouldn't work if called straight after adapter.submitList. It is because the differ looks for changes in a background thread and then asynchronously notifies adapter about changes. On a SO i have seen several wrong answers with unnecessary delays & etc to solve this.
To handle the situation properly the submitList has a callback which is invoked when changes have been applied.
So the proper kotlin implementations in this case are:
//memorise target item here and a scroll offset if needed
adapter.submitList(items) {
val pos = /* here you may find a new position of the item or just use just a static position. It depends on your case */
recyclerView.scrollToPosition(pos)
}
//or
adapter.submitList(items) { recyclerView.smoothScrollToPosition(pos) }
//or etc
adapter.submitList(items) { (recyclerView.layoutManager as LinearLayoutManager).scrollToPositionWithOffset(pos, offset) }
Introduction
None of the answers explain how to show last item(s) at the top. So, the answers work only for items that still have enough items above or below them to fill the remaining RecyclerView. For instance, if there are 59 elements and a 56-th element is selected it should be at the top as in the picture below:
So, let's see how to implement this in the next paragraph.
Solution
We could handle those cases by using linearLayoutManager.scrollToPositionWithOffset(pos, 0) and additional logic in the Adapter of RecyclerView - by adding a custom margin below the last item (if the last item is not visible then it means there's enough space fill the RecyclerView). The custom margin could be a difference between the root view height and the item height. So, your Adapter for RecyclerView would look as follows:
...
#Override
public void onBindViewHolder(ViewHolder holder, final int position) {
...
int bottomHeight = 0;
int itemHeight = holder.itemView.getMeasuredHeight();
// if it's the last item then add a bottom margin that is enough to bring it to the top
if (position == mDataSet.length - 1) {
bottomHeight = Math.max(0, mRootView.getMeasuredHeight() - itemHeight);
}
RecyclerView.LayoutParams params = (RecyclerView.LayoutParams)holder.itemView.getLayoutParams();
params.setMargins(0, 0, params.rightMargin, bottomHeight);
holder.itemView.setLayoutParams(params);
...
}
...
If your LayoutManager is LinearLayoutManager you can use scrollToPositionWithOffset(position,0); on it and it will make your item the first visible item in the list. Otherwise, you can use smoothScrollToPosition on the RecyclerView directly.
I ended up using the below code.
RecyclerView.LayoutManager layoutManager = mainList.getLayoutManager();
if (layoutManager instanceof LinearLayoutManager) {
// Scroll to item and make it the first visible item of the list.
((LinearLayoutManager) layoutManager).scrollToPositionWithOffset(position, 0);
} else {
mainList.smoothScrollToPosition(position);
}
scroll at particular position
and this helped me alot.
by click listener you can get the position in your adapter
layoutmanager.scrollToPosition(int position);
In my case my RecyclerView have a padding top like this
<android.support.v7.widget.RecyclerView
...
android:paddingTop="100dp"
android:clipToPadding="false"
/>
Then for scroll a item to top, I need to
recyclerViewLinearLayoutManager.scrollToPositionWithOffset(position, -yourRecyclerView.getPaddingTop());
please note that if scrollToPosition not work notice that your RecyclerView was inside a NestedScrollView; refer to this post
This is pretty simple
recyclerView.scrollToPosition(position)
If you've Recycler view inside nestedscrollview :
val y = recyclerview.getChildAt(0).y
recyclerview.smoothScrollTo(0, y.toInt())
If your Recycler view is not inside nestedscrollview :
recyclerview.smoothScrollToPosition(index)
or
recyclerview.layoutManager?.smoothScrollToPosition(recyclerview, null ,index)
I use the code below to smooth-scroll an item (thisView) to the top.
It works also for GridLayoutManager with views of different heights:
View firstView = mRecyclerView.getChildAt(0);
int toY = firstView.getTop();
int firstPosition = mRecyclerView.getChildAdapterPosition(firstView);
View thisView = mRecyclerView.getChildAt(thisPosition - firstPosition);
int fromY = thisView.getTop();
mRecyclerView.smoothScrollBy(0, fromY - toY);
Seems to work good enough for a quick solution.
I need to know which elements are currently displayed in my RecyclerView. There is no equivalent to the OnScrollListener.onScroll(...) method on ListViews. I tried to work with View.getGlobalVisibleRect(...), but that hack is too ugly and does not always work too.
Someone any ideas?
First / last visible child depends on the LayoutManager.
If you are using LinearLayoutManager or GridLayoutManager, you can use
int findFirstVisibleItemPosition();
int findFirstCompletelyVisibleItemPosition();
int findLastVisibleItemPosition();
int findLastCompletelyVisibleItemPosition();
For example:
GridLayoutManager layoutManager = ((GridLayoutManager)mRecyclerView.getLayoutManager());
int firstVisiblePosition = layoutManager.findFirstVisibleItemPosition();
For LinearLayoutManager, first/last depends on the adapter ordering. Don't query children from RecyclerView; LayoutManager may prefer to layout more items than visible for caching.
For those who have a logic to be implemented inside the RecyclerView adapter, you can still use the #ernesto approach combined with an on scrollListener to get what you want as the RecyclerView is consulted.
Inside the adapter you will have something like this:
#Override
public void onAttachedToRecyclerView(#NonNull RecyclerView recyclerView) {
super.onAttachedToRecyclerView(recyclerView);
RecyclerView.LayoutManager manager = recyclerView.getLayoutManager();
if(manager instanceof LinearLayoutManager && getItemCount() > 0) {
LinearLayoutManager llm = (LinearLayoutManager) manager;
recyclerView.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);
int visiblePosition = llm.findFirstCompletelyVisibleItemPosition();
if(visiblePosition > -1) {
View v = llm.findViewByPosition(visiblePosition);
//do something
v.setBackgroundColor(Color.parseColor("#777777"));
}
}
});
}
}
Finally, I found a solution to know if the current item is visible, from the onBindViewHolder event in the adapter.
The key is the method isViewPartiallyVisible from LayoutManager.
In your adapter, you can get the LayoutManager from the RecyclerView, which you get as parameter from the onAttachedToRecyclerView event.
You can use recyclerView.getChildAt() to get each visible child, and setting some tag convertview.setTag(index) on these view in adapter code will help you to relate it with adapter data.
Addendum:
The proposed functions findLast...Position() do not work correctly in a scenario with a collapsing toolbar while the toolbar is expanded.
It seems that the recycler view has a fixed height, and while the toolbar is expanded, the recycler is moved down, partially out of the screen. As a consequence the results of the proposed functions are too high. Example: The last visible item is told to be #9, but in fact item #7 is the last one that is on screen.
This behaviour is also the reason why my view often failed to scroll to the correct position, i.e. scrollToPosition() did not work correctly (I finally collapsed the toolbar programmatically).
Every answer above is correct and I would like to add also a snapshot from my working codes.
recycler.addOnScrollListener(new RecyclerView.OnScrollListener() {
#Override
public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
super.onScrollStateChanged(recyclerView, newState);
// Some code when initially scrollState changes
}
#Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
// Some code while the list is scrolling
LinearLayoutManager lManager = (LinearLayoutManager) recyclerView.getLayoutManager();
int firstElementPosition = lManager.findFirstVisibleItemPosition();
}
});
Following Linear / Grid LayoutManager methods can be used to check which items are visible.
int findFirstVisibleItemPosition();
int findLastVisibleItemPosition();
int findFirstCompletelyVisibleItemPosition();
int findLastCompletelyVisibleItemPosition();
and if you want to track is item visible on screen for some threshold then you can refer to the following blog.
https://proandroiddev.com/detecting-list-items-perceived-by-user-8f164dfb1d05
For StaggeredGridLayoutManager do this:
RecyclerView rv = findViewById(...);
StaggeredGridLayoutManager lm = new StaggeredGridLayoutManager(...);
rv.setLayoutManager(lm);
And to get visible item views:
int[] viewsIds = lm.findFirstCompletelyVisibleItemPositions(null);
ViewHolder firstViewHolder = rvPlantios.findViewHolderForLayoutPosition(viewsIds[0]);
View itemView = viewHolder.itemView;
Remember to check if it is empty.
You can find the first and last visible children of the recycle view and check if the view you're looking for is in the range:
var visibleChild: View = rv.getChildAt(0)
val firstChild: Int = rv.getChildAdapterPosition(visibleChild)
visibleChild = rv.getChildAt(rv.childCount - 1)
val lastChild: Int = rv.getChildAdapterPosition(visibleChild)
println("first visible child is: $firstChild")
println("last visible child is: $lastChild")
For those who are looking for an answer in Kotlin:
fun getVisibleItem(recyclerView : RecyclerView) {
recyclerView.addOnScrollListener(object: RecyclerView.OnScrollListener() {
override fun onScrollStateChanged(recyclerView: RecyclerView, newState: Int) {
if(newState == RecyclerView.SCROLL_STATE_IDLE) {
val index = (recyclerView.layoutManager.findFirstVisibleItemPosition
//use this index for any operation you want to perform on the item visible on screen. eg. log(arrayList[index])
}
}
})
}
You can explore other methods for getting the position as per your use case.
int findFirstCompletelyVisibleItemPosition()
int findLastVisibleItemPosition()
int findLastCompletelyVisibleItemPosition()
if the visible item position is different from the item position toast message will show on the screen.
myRecyclerview.addOnScrollListener(new RecyclerView.OnScrollListener() {
#Override
public void onScrollStateChanged(#NonNull RecyclerView recyclerView, int newState) {
super.onScrollStateChanged(recyclerView, newState);
LinearLayoutManager manager= (LinearLayoutManager) myRecyclerview.getLayoutManager();
assert manager != null;
int visiblePosition = manager.findLastCompletelyVisibleItemPosition();
if(visiblePosition > -1&&a!=visiblePosition) {
Toast.makeText(context,String.valueOf(visiblePosition),Toast.LENGTH_SHORT).show();
//do something
a=visiblePosition;
}
}
#Override
public void onScrolled(#NonNull RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
//Some code while the list is scrolling
}
});
I need to know which elements are currently displayed in my RecyclerView. There is no equivalent to the OnScrollListener.onScroll(...) method on ListViews. I tried to work with View.getGlobalVisibleRect(...), but that hack is too ugly and does not always work too.
Someone any ideas?
First / last visible child depends on the LayoutManager.
If you are using LinearLayoutManager or GridLayoutManager, you can use
int findFirstVisibleItemPosition();
int findFirstCompletelyVisibleItemPosition();
int findLastVisibleItemPosition();
int findLastCompletelyVisibleItemPosition();
For example:
GridLayoutManager layoutManager = ((GridLayoutManager)mRecyclerView.getLayoutManager());
int firstVisiblePosition = layoutManager.findFirstVisibleItemPosition();
For LinearLayoutManager, first/last depends on the adapter ordering. Don't query children from RecyclerView; LayoutManager may prefer to layout more items than visible for caching.
For those who have a logic to be implemented inside the RecyclerView adapter, you can still use the #ernesto approach combined with an on scrollListener to get what you want as the RecyclerView is consulted.
Inside the adapter you will have something like this:
#Override
public void onAttachedToRecyclerView(#NonNull RecyclerView recyclerView) {
super.onAttachedToRecyclerView(recyclerView);
RecyclerView.LayoutManager manager = recyclerView.getLayoutManager();
if(manager instanceof LinearLayoutManager && getItemCount() > 0) {
LinearLayoutManager llm = (LinearLayoutManager) manager;
recyclerView.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);
int visiblePosition = llm.findFirstCompletelyVisibleItemPosition();
if(visiblePosition > -1) {
View v = llm.findViewByPosition(visiblePosition);
//do something
v.setBackgroundColor(Color.parseColor("#777777"));
}
}
});
}
}
Finally, I found a solution to know if the current item is visible, from the onBindViewHolder event in the adapter.
The key is the method isViewPartiallyVisible from LayoutManager.
In your adapter, you can get the LayoutManager from the RecyclerView, which you get as parameter from the onAttachedToRecyclerView event.
You can use recyclerView.getChildAt() to get each visible child, and setting some tag convertview.setTag(index) on these view in adapter code will help you to relate it with adapter data.
Addendum:
The proposed functions findLast...Position() do not work correctly in a scenario with a collapsing toolbar while the toolbar is expanded.
It seems that the recycler view has a fixed height, and while the toolbar is expanded, the recycler is moved down, partially out of the screen. As a consequence the results of the proposed functions are too high. Example: The last visible item is told to be #9, but in fact item #7 is the last one that is on screen.
This behaviour is also the reason why my view often failed to scroll to the correct position, i.e. scrollToPosition() did not work correctly (I finally collapsed the toolbar programmatically).
Every answer above is correct and I would like to add also a snapshot from my working codes.
recycler.addOnScrollListener(new RecyclerView.OnScrollListener() {
#Override
public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
super.onScrollStateChanged(recyclerView, newState);
// Some code when initially scrollState changes
}
#Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
// Some code while the list is scrolling
LinearLayoutManager lManager = (LinearLayoutManager) recyclerView.getLayoutManager();
int firstElementPosition = lManager.findFirstVisibleItemPosition();
}
});
Following Linear / Grid LayoutManager methods can be used to check which items are visible.
int findFirstVisibleItemPosition();
int findLastVisibleItemPosition();
int findFirstCompletelyVisibleItemPosition();
int findLastCompletelyVisibleItemPosition();
and if you want to track is item visible on screen for some threshold then you can refer to the following blog.
https://proandroiddev.com/detecting-list-items-perceived-by-user-8f164dfb1d05
For StaggeredGridLayoutManager do this:
RecyclerView rv = findViewById(...);
StaggeredGridLayoutManager lm = new StaggeredGridLayoutManager(...);
rv.setLayoutManager(lm);
And to get visible item views:
int[] viewsIds = lm.findFirstCompletelyVisibleItemPositions(null);
ViewHolder firstViewHolder = rvPlantios.findViewHolderForLayoutPosition(viewsIds[0]);
View itemView = viewHolder.itemView;
Remember to check if it is empty.
You can find the first and last visible children of the recycle view and check if the view you're looking for is in the range:
var visibleChild: View = rv.getChildAt(0)
val firstChild: Int = rv.getChildAdapterPosition(visibleChild)
visibleChild = rv.getChildAt(rv.childCount - 1)
val lastChild: Int = rv.getChildAdapterPosition(visibleChild)
println("first visible child is: $firstChild")
println("last visible child is: $lastChild")
For those who are looking for an answer in Kotlin:
fun getVisibleItem(recyclerView : RecyclerView) {
recyclerView.addOnScrollListener(object: RecyclerView.OnScrollListener() {
override fun onScrollStateChanged(recyclerView: RecyclerView, newState: Int) {
if(newState == RecyclerView.SCROLL_STATE_IDLE) {
val index = (recyclerView.layoutManager.findFirstVisibleItemPosition
//use this index for any operation you want to perform on the item visible on screen. eg. log(arrayList[index])
}
}
})
}
You can explore other methods for getting the position as per your use case.
int findFirstCompletelyVisibleItemPosition()
int findLastVisibleItemPosition()
int findLastCompletelyVisibleItemPosition()
if the visible item position is different from the item position toast message will show on the screen.
myRecyclerview.addOnScrollListener(new RecyclerView.OnScrollListener() {
#Override
public void onScrollStateChanged(#NonNull RecyclerView recyclerView, int newState) {
super.onScrollStateChanged(recyclerView, newState);
LinearLayoutManager manager= (LinearLayoutManager) myRecyclerview.getLayoutManager();
assert manager != null;
int visiblePosition = manager.findLastCompletelyVisibleItemPosition();
if(visiblePosition > -1&&a!=visiblePosition) {
Toast.makeText(context,String.valueOf(visiblePosition),Toast.LENGTH_SHORT).show();
//do something
a=visiblePosition;
}
}
#Override
public void onScrolled(#NonNull RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
//Some code while the list is scrolling
}
});