I have implemented a horizontal scrollable RecyclerView. My RecyclerView uses a LinearLayoutManager, and the problem I am facing is that when I try to use scrollToPosition(position) or smoothScrollToPosition(position) or from LinearLayoutManager's scrollToPositionWithOffset(position). Neither works for me. Either a scroll call doesn't scroll to the desired location or it doesn't invoke the OnScrollListener.
So far I have tried so many different combinations of code that I cannot post them all here. Following is the one that works for me (But only partially):
public void smoothUserScrollTo(final int position) {
if (position < 0 || position > getAdapter().getItemCount()) {
Log.e(TAG, "An attempt to scroll out of adapter size has been stopped.");
return;
}
if (getLayoutManager() == null) {
Log.e(TAG, "Cannot scroll to position a LayoutManager is not set. " +
"Call setLayoutManager with a non-null layout.");
return;
}
if (getChildAdapterPosition(getCenterView()) == position) {
return;
}
stopScroll();
scrollToPosition(position);
if (lastScrollPosition == position) {
addOnLayoutChangeListener(new OnLayoutChangeListener() {
#Override
public void onLayoutChange(View v, int left, int top, int right, int bottom, int oldLeft, int oldTop, int oldRight, int oldBottom) {
if (left == oldLeft && right == oldRight && top == oldTop && bottom == oldBottom) {
removeOnLayoutChangeListener(this);
updateViews();
// removing the following line causes a position - 3 effect.
scrollToView(getChildAt(0));
}
}
});
}
lastScrollPosition = position;
}
#Override
public void scrollToPosition(int position) {
if (position < 0 || position > getAdapter().getItemCount()) {
Log.e(TAG, "An attempt to scroll out of adapter size has been stopped.");
return;
}
if (getLayoutManager() == null) {
Log.e(TAG, "Cannot scroll to position a LayoutManager is not set. " +
"Call setLayoutManager with a non-null layout.");
return;
}
// stopScroll();
((LinearLayoutManager) getLayoutManager()).scrollToPositionWithOffset(position, 0);
// getLayoutManager().scrollToPosition(position);
}
I opted for scrollToPositionWithOffset() because of this but the case perhaps is different as I use a LinearLayoutManager instead of GridLayoutManager. But the solution does work for me too, but as I said earlier only partially.
When the call to scroll is from 0th position to totalSize - 7 scroll works like a charm.
When scroll is from totalSize - 7 to totalSize - 3, First time I only scroll to 7th last item in the list. The second time however I can scroll fine
When scrolling from totalSize - 3 to totalSize, I start getting unexpected behavior.
If anyone has found a work around I'd Appreciate it. Here's the gist to my code of custom ReyclerView.
I had the same issue some weeks ago, and found only a really bad solution to solve it. Had to use a postDelayed with 200-300ms.
new Handler().postDelayed(new Runnable() {
#Override
public void run() {
yourList.scrollToPosition(position);
}
}, 200);
If you found a better solution, please let me know! Good luck!
Turns out I was having a similar issue until I utilized
myRecyclerview.scrollToPosition(objectlist.size()-1)
It would always stay at the top when only putting in the objectlist size. This was until i decided to set the size equal to a variable. Again, that didn't work. Then I assumed that perhaps it was handling an outofboundsexception without telling me. So I subtracted it by 1. Then it worked.
The accepted answer will work, but it may also break. The main reason for this issue is that the recycler view may not be ready by the time you ask it to scroll. The best solution for the same is to wait for the recycler view to be ready and then scroll. Luckily android has provided one such option. Below solution is for Kotlin, you can try the java alternative for the same, it will work.
newsRecyclerView.post {
layoutManager?.scrollToPosition(viewModel.selectedItemPosition)
}
The post runnable method is available for every View elements and will execute once the view is ready, hence ensuring the code is executed exactly when required.
You can use LinearSmoothScroller this worked every time in my case:
First create an instance of LinearSmoothScroller:
LinearSmoothScroller smoothScroller=new LinearSmoothScroller(activity){
#Override
protected int getVerticalSnapPreference() {
return LinearSmoothScroller.SNAP_TO_START;
}
};
And then when you want to scroll recycler view to any position do this:
smoothScroller.setTargetPosition(pos); // pos on which item you want to scroll recycler view
recyclerView.getLayoutManager().startSmoothScroll(smoothScroller);
Done.
So the problem for me was that I had a RecyclerView in a NestedScrollView. Took me some time to figure out this was the problem. The solution for this is (Kotlin):
val childY = recycler_view.y + recycler_view.getChildAt(position).y
nested_scrollview.smoothScrollTo(0, childY.toInt())
Java (credits to Himagi https://stackoverflow.com/a/50367883/2917564)
float y = recyclerView.getY() + recyclerView.getChildAt(selectedPosition).getY();
scrollView.smoothScrollTo(0, (int) y);
The trick is to scroll the nested scrollview to the Y instead of the RecyclerView. This works decently at Android 5.0 Samsung J5 and Huawei P30 pro with Android 9.
I also faced a similar problem (having to scroll to the top when the list is getting updated), but none of the above options worked 100%
However I finally found a working solution at https://dev.to/aldok/how-to-scroll-recyclerview-to-a-certain-position-5ck4 archive link
Summary
scrollToPosition only seems to work when the underlying dataset is ready.
So therefore postDelay works (randomly) but it's depending on the speed of the device/app. If the timeout is too short it fails. smoothScrollToPosition also only works if the adapter is not too busy (see https://stackoverflow.com/a/61403576/11649486)
To observe when the dataset is ready, a AdapterDataObserver can be added and certain methods overridden.
The code that fixed my problem:
adapter.registerAdapterDataObserver( object : RecyclerView.AdapterDataObserver() {
override fun onItemRangeInserted(
positionStart: Int,
itemCount: Int
) {
// This will scroll to the top when new data was inserted
recyclerView.scrollToPosition(0)
}
}
None of the methods seems to be working for me. Only the below single line of code worked
((LinearLayoutManager)mRecyclerView.getLayoutManager()).scrollToPositionWithOffset(adapter.currentPosition(),200);
The second parameter refers to offset, which is actually the distance (in pixels) between the start edge of the item view and start edge of the RecyclerView. I have supplied it with a constant value to make the top items also visible.
Check for more reference over here
Using Kotlin Coroutines in Fragment or Activity, and also using the lifecycleScope since any coroutine launched in this scope is canceled when the Lifecycle is destroyed.
lifecycleScope.launch {
delay(100)
recyclerView.scrollToPosition(0)
This worked for me
Handler().postDelayed({
(recyclerView.getLayoutManager() as LinearLayoutManager).scrollToPositionWithOffset( 0, 0)
}, 100)
I had the same issue while creating a cyclic/circular adapter, where I could only scroll downward but not upward considering the position initialises to 0. I first considered using Robert's approach, but it was too unreliable as the Handler only fired once, and if I was unlucky the position wouldn't get initialised in some cases.
To resolve this, I create an interval Observable that checks every XXX amount of time to see whether the initialisation succeeded and afterward disposes of it. This approach worked very reliably for my use case.
private fun initialisePositionToAllowBidirectionalScrolling(layoutManager: LinearLayoutManager, realItemCount: Int) {
val compositeDisposable = CompositeDisposable() // Added here for clarity, make this into a private global variable and clear in onDetach()/onPause() in case auto-disposal wouldn't ever occur here
val initPosition = realItemCount * 1000
Observable.interval(INIT_DELAY_MS, TimeUnit.MILLISECONDS)
.observeOn(AndroidSchedulers.mainThread())
.subscribe ({
if (layoutManager.findFirstVisibleItemPosition() == 0) {
layoutManager.scrollToPositionWithOffset(initPosition, 0)
if (layoutManager.findFirstCompletelyVisibleItemPosition() == initPosition) {
Timber.d("Adapter initialised, setting position to $initPosition and disposing interval subscription!")
compositeDisposable.clear()
}
}
}, {
Timber.e("Failed to initialise position!\n$it")
compositeDisposable.clear()
}).let { compositeDisposable.add(it) }
}
This worked perfectly for when scrolling to last item in the recycler
Handler handler = new Handler();
handler.postDelayed(new Runnable() {
#Override
public void run() {
if (((LinearLayoutManager) recyclerView.getLayoutManager())
.findLastVisibleItemPosition() != adapter.getItemCount() - 1) {
recyclerView.scrollToPosition(adapter.getItemCount() - 1);
handler.postDelayed(this, 200);
}
}
}, 200 /* change it if you want*/);
Pretty weird bug, anyway I managed to work around it without post or post delayed as follow:
list.scrollToPosition(position - 1)
list.smoothScrollBy(1, 0)
Hopefully, it helps someone too.
Had the same issue. My problem was, that I refilled the view with data in an async task, after I tried to scroll. From onPostExecute ofc fixed this problem. A Delay fixed this issue too, because when the scroll executed, the list had already been refilled.
I use below solution to make the selected item in recycler view visible after the recycler view is reloaded (orientation change, etc). It overrides LinearLayoutManager and uses onSaveInstanceState to save current recycler position. Then in onRestoreInstanceState the saved position is restored. Finaly, in onLayoutCompleted, scrollToPosition(mRecyclerPosition) is used to make the previously selected recycler position visible again, but as Robert Banyai stated, for it to work reliably a certain delay must be inserted. I guess it is needed to provide enough time for adapter to load the data before scrollToPosition is called.
private class MyLayoutManager extends LinearLayoutManager{
private boolean isRestored;
public MyLayoutManager(Context context) {
super(context);
}
public MyLayoutManager(Context context, int orientation, boolean reverseLayout) {
super(context, orientation, reverseLayout);
}
public MyLayoutManager(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
super(context, attrs, defStyleAttr, defStyleRes);
}
#Override
public void onLayoutCompleted(RecyclerView.State state) {
super.onLayoutCompleted(state);
if(isRestored && mRecyclerPosition >-1) {
Handler handler=new Handler();
handler.postDelayed(new Runnable() {
#Override
public void run() {
MyLayoutManager.this.scrollToPosition(mRecyclerPosition);
}
},200);
}
isRestored=false;
}
#Override
public Parcelable onSaveInstanceState() {
Parcelable savedInstanceState = super.onSaveInstanceState();
Bundle bundle=new Bundle();
bundle.putParcelable("saved_state",savedInstanceState);
bundle.putInt("position", mRecyclerPosition);
return bundle;
}
#Override
public void onRestoreInstanceState(Parcelable state) {
Parcelable savedState = ((Bundle)state).getParcelable("saved_state");
mRecyclerPosition = ((Bundle)state).getInt("position",-1);
isRestored=true;
super.onRestoreInstanceState(savedState);
}
}
If you use recyclerview in nestedScrollView you must scroll nestScrollview
nestedScrollview.smoothScrollTo(0,0)
Maybe It's not so elegant way to do it, But this always works for me. Add a new method to the RecyclerView and use it insted of scrollToPosition:
public void myScrollTo(int pos){
stopScroll();
((LinearLayoutManager)getLayoutManager()).scrollToPositionWithOffset(pos,0);
}
The answer is to use the Post Method, it will guarantee correct execution for any action
This is the ultimate solution using kotlin in this date ... if you navigate to another fragment and go back and your recyclerview resets to the first position just add this line in onCreateView or wherever you need can call the adapter...
pagingAdapter.stateRestorationPolicy=RecyclerView.Adapter.StateRestorationPolicy.PREVENT_WHEN_EMPTY
BTW pagingAdapter is my adapter with diffUtil.
I had a similar issue, (but not the same), I try to explain it, maybe be could help someone else:
By the time I call to 'scrollToPosition' dataset is already set but some content like images loaded async (using Glide library) and probably when RecyclerView tries to compute the height amount to scroll down, image should return 0 as no loaded yet. So that gives an inaccurate scroll down I could solve it that way:
fun LinearLayoutManager.accurateScrollToPosition(position: Int) {
this.scrollToPosition(position)
this.postOnAnimation {
val realPosition = this.findFirstVisibleItemPosition()
if (position != realPosition) {
this.accurateScrollToPosition(position)
} else {
this.scrollToPosition(position) // this looks redunadant or inecessary but must be call to ensure accurate scroll
}
}
}
PD: In my case was not possible to know the size of the image to be loaded, if you know or you can resize the image you can add a placeholder on glide with de image size or override de size so recyclerView can compute the size correctly and don't need the above walkaraound.
I have used custom coveflow, everything works fine when i load small amount of data, but it doesn't work with large amount of data,
check it out my below code
if (mAdapter == null || mAdapter.getCount() == 0)
throw new IllegalStateException(
"You are trying to scroll container with no adapter set. Set adapter first.");
if (mLastCenterItemIndex != -1) {
final int lastCenterItemPosition = (mFirstItemPosition + mLastCenterItemIndex)
% mAdapter.getCount();
final int di = lastCenterItemPosition - position;
final int dst = (int) (di * mCoverWidth * mSpacing);
mScrollToPositionOnNextInvalidate = -1;
scrollBy(-dst, 0);
} else {
mScrollToPositionOnNextInvalidate = position;
}
invalidate();
i have used this code to move my item to center of the tablet, now i am gng to explain my view, in one activity half of my screen occupies coverflow and other half occupies mapview, when i click map marker icon i need to move particular item to center of my screen in coverflow, so basically my coverflow and map sync, the changes must affect both,
it works perfectly when i load small amount of data, but now i tried to load 11000 records when i click marker then my UI gets blocked becuase of scrollby in Coverflow, can you suggest any idea to move my item center?? or is there any method which doesn't affect UI
All suggestion are most welcome
Thanks
Just include your code in
new Thread(new Runnable() {
public void run () {
//.........
}
}).start();
or load items by parts
I have a listView with a custom adapter. When something happens (a click in a child) I do some calculation things and modify the child View. IF some condition has been fulfilled then other child unrelated to the clicked child should be modified.
This sometimes works, but sometimes fails and the DDMS says that the view is null...
Let me show you the code:
if(invalidaEste != -1)
{
try
{
View v = lv_data.getChildAt(invalidaEste);
if( v== null)
{
Log.e("MY_LOG", "SIZE " + lv_data.getCount());
Log.e("MY_LOG", "IS_NULL " + String.valueOf(invalidaEste));
}
if(invalidaEste >= lv_data.getFirstVisiblePosition() &&
invalidaEste <= lv_data.getLastVisiblePosition())
{
RelacionFacturaPago rpf = (RelacionFacturaPago)lv_data.getAdapter().getItem(invalidaEste);
TextView tv = (TextView)v.findViewById(R.id.tv_pendiente);
tv.setText(Formato.double2Screen(rpf.getPorPagar()));
}
}
catch (Exception e)
{
Log.e("MY_LOG", "FAIL");
Log.e("MY_LOG", String.valueOf(invalidaEste));
}
}
invalidaEste is the view that I want to modify.
When v is null I log the index to check if it is OK. Always is smaller or equal than the listView.getCount()
Why is this happening?
More data: The code is inside of the onAnimationStart(Animation animation) of an AnimationListener listener.
Because of view recycling, listView.getChildAt() will only return a view for the positions it is displaying, and maybe one more. Maybe if you share more of your code we can help you figure out how to best tackle the problem.
Dmon and Azertiti are both correct... once your list is scrolled you find yourself in trouble. If the view isn't visible, then it doesn't exist (i.e. has been recycled by Android). You'll re-build the view once it's scrolled in.
Doing something like this should work:
View view;
int nFirstPos = lv_data.getFirstVisiblePosition();
int nWantedPos = invalidaEste - nFirstPos;
if ((nWantedPos >= 0) && (nWantedPos <= lv_data.getChildCount())
{
view = lv_data.getChildAt(nWantedPos);
if (view == null)
return;
// else we have the view we want
}
If that child is not visible on screen it means there is no View for it. I believe this is your not working case.
A good practice is to change the data behind your list adapter and call notifyDataSetChanged() on the adapter. This will inform the list the adapter has changed and paint again the views.
If you really want to manually update the view I guess the only solution is to retain the new values somewhere and wait until the View becomes visible. At that point you have a valid reference and can do the updates.
I test it with one line of code when I need to go within a valid position of a Listview. here is your variables used as an example. where lv_data is the ListView and tv is your TextView.
if ( lv_data.getChildAt(lv_data.getPositionForView(tv)) != null) {
int position = lv_data.getPositionForView(tv);
}
I'm creating a list of pictures using a ListView and the photos are of a size that would fit 2 to 3 photos on the screen.
The problem that I'm having is that I would like to when the user stops scrolling that the first item of the visible list would snap to the top of screen, for example, if the scroll ends and small part of the first picture displayed, we scroll the list down so the picture is always fully displayed, if mostly of the picture is displayed, we scroll the list up so the next picture is fully visible.
Is there a way to achieve this in android with the listview?
I've found a way to do this just listening to scroll and change the position when the scroll ended by implementing ListView.OnScrollListener
#Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
switch (scrollState) {
case OnScrollListener.SCROLL_STATE_IDLE:
if (scrolling){
// get first visible item
View itemView = view.getChildAt(0);
int top = Math.abs(itemView.getTop()); // top is a negative value
int bottom = Math.abs(itemView.getBottom());
if (top >= bottom){
((ListView)view).setSelectionFromTop(view.getFirstVisiblePosition()+1, 0);
} else {
((ListView)view).setSelectionFromTop(view.getFirstVisiblePosition(), 0);
}
}
scrolling = false;
break;
case OnScrollListener.SCROLL_STATE_TOUCH_SCROLL:
case OnScrollListener.SCROLL_STATE_FLING:
Log.i("TEST", "SCROLLING");
scrolling = true;
break;
}
}
The change is not so smooth but it works.
Utilizing a couple ideas from #nininho's solution, I got my listview to snap to the item with a smooth scroll instead of abruptly going to it. One caveat is that I've only tested this solution on a Moto X in a basic ListView with text, but it works very well on the device. Nevertheless, I'm confident about this solution, and encourage you to provide feedback.
listview.setOnScrollListener(new OnScrollListener() {
#Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
// TODO Auto-generated method stub
if (scrollState == SCROLL_STATE_IDLE) {
View itemView = view.getChildAt(0);
int top = Math.abs(itemView.getTop());
int bottom = Math.abs(itemView.getBottom());
int scrollBy = top >= bottom ? bottom : -top;
if (scrollBy == 0) {
return;
}
smoothScrollDeferred(scrollBy, (ListView)view);
}
}
private void smoothScrollDeferred(final int scrollByF,
final ListView viewF) {
final Handler h = new Handler();
h.post(new Runnable() {
#Override
public void run() {
// TODO Auto-generated method stub
viewF.smoothScrollBy(scrollByF, 200);
}
});
}
#Override
public void onScroll(AbsListView view, int firstVisibleItem,
int visibleItemCount, int totalItemCount) {
// TODO Auto-generated method stub
}
});
The reason I defer the smooth scrolling is because in my testing, directly calling the smoothScrollBy method in the state changed callback had problems actually scrolling. Also, I don't foresee a fully-tested, robust solution holding very much state, and in my solution below, I hold no state at all. This solution is not yet in the Google Play Store, but should serve as a good starting point.
Using #nininho 's solution,
In the onScrollStateChanged when the state changes to SCROLL_STATE_IDLE, remember the position to snap and raise a flag:
snapTo = view.getFirstVisiblePosition();
shouldSnap = true;
Then, override the computeScroll() method:
#Override
public void computeScroll() {
super.computeScroll();
if(shouldSnap){
this.smoothScrollToPositionFromTop(snapTo, 0);
shouldSnap = false;
}
}
You can do a much more smooth scrolling if you use RecyclerView. The OnScrollListener is way better.
I have made an example here: https://github.com/plattysoft/SnappingList
Well.. I know 10 years have past since this question was asked, but now we can use LinearSnapHelper:
new LinearSnapHelper().attachToRecyclerView(recyclerView);
Source:
https://proandroiddev.com/android-recyclerview-snaphelper-19eaa9598da6
Apart from trying the code above one thing you should make sure of is that your listView have a height that can fit exact number of items you want to be displayed.
e.g
If you want 4 items to be displayed after snap effect and your row height (defined in its layout) should be 1/4 of the total height of the list.
Note that after the smoothScrollBy() call, getFirstVisiblePosition() may point to the list item ABOVE the topmost one in the listview. This is especially true when view.getChildAt(0).getBottom() == 0. I had to call view.setSelection(view.getFirstVisiblePosition() + 1) to remedy this odd behavior.
I am using it, but it always returns 0, even though I have scrolled till the end of the list.
getScrollY() is actually a method on View, not ListView. It is referring to the scroll amount of the entire view, so it will almost always be 0.
If you want to know how far the ListView's contents are scrolled, you can use listView.getFirstVisiblePosition();
It does work, it returns the top part of the scrolled portion of the view in pixels from the top of the visible view. See the getScrollY() documentation. Basically if your list is taking up the full view then you will always get 0, because the top of the scrolled portion of the list is always at the top of the screen.
What you want to do to see if you are at the end of a list is something like this:
public void onCreate(final Bundle bundle) {
super.onCreate(bundle);
setContentView(R.layout.main);
// The list defined as field elswhere
this.view = (ListView) findViewById(R.id.searchResults);
this.view.setOnScrollListener(new OnScrollListener() {
private int priorFirst = -1;
#Override
public void onScroll(final AbsListView view, final int first, final int visible, final int total) {
// detect if last item is visible
if (visible < total && (first + visible == total)) {
// see if we have more results
if (first != priorFirst) {
priorFirst = first;
//Do stuff here, last item is displayed, end of list reached
}
}
}
});
}
The reason for the priorFirst counter is that sometimes scroll events can be generated multiple times, so you only need to react to the first time the end of the list is reached.
If you are trying to do an auto-growing list, I'd suggest this tutorial.
You need two things to precisely define the scroll position of a listView:
To get current position:
int firstVisiblePosition = listView.getFirstVisiblePosition();
int topEdge=listView.getChildAt(0).getTop(); //This gives how much the top view has been scrolled.
To set the position:
listView.setSelectionFromTop(firstVisiblePosition,0);
// Note the '-' sign for scrollTo..
listView.scrollTo(0,-topEdge);