I'm trying to smoothly scroll to last element of a list after adding an element to the arrayadapter associated with the listview.
The problem is that it just scrolls to a random position
arrayadapter.add(item);
//DOES NOT WORK CORRECTLY:
listview.smoothScrollToPosition(arrayadapter.getCount()-1);
//WORKS JUST FINE:
listview.setSelection(arrayadapter.getCount()-1);
You probably want to tell the ListView to post the scroll when the UI thread can handle it (which is why yours it not scrolling properly). SmoothScroll needs to do a lot of work, as opposed to just go to a position ignoring velocity/time/etc. (required for an "animation").
Therefore you should do something like:
getListView().post(new Runnable() {
#Override
public void run() {
getListView().smoothScrollToPosition(pos);
}
});
(Copied from my answer: smoothScrollToPositionFromTop() is not always working like it should)
This is a known bug. See https://code.google.com/p/android/issues/detail?id=36062
However, I implemented this workaround that deals with all edge cases that might occur:
First call smothScrollToPositionFromTop(position) and then, when scrolling has finished, call setSelection(position). The latter call corrects the incomplete scrolling by jumping directly to the desired position. Doing so the user still has the impression that it is being animation-scrolled to this position.
I implemented this workaround within two helper methods:
smoothScrollToPosition()
public static void smoothScrollToPosition(final AbsListView view, final int position) {
View child = getChildAtPosition(view, position);
// There's no need to scroll if child is already at top or view is already scrolled to its end
if ((child != null) && ((child.getTop() == 0) || ((child.getTop() > 0) && !view.canScrollVertically(1)))) {
return;
}
view.setOnScrollListener(new AbsListView.OnScrollListener() {
#Override
public void onScrollStateChanged(final AbsListView view, final int scrollState) {
if (scrollState == SCROLL_STATE_IDLE) {
view.setOnScrollListener(null);
// Fix for scrolling bug
new Handler().post(new Runnable() {
#Override
public void run() {
view.setSelection(position);
}
});
}
}
#Override
public void onScroll(final AbsListView view, final int firstVisibleItem, final int visibleItemCount,
final int totalItemCount) { }
});
// Perform scrolling to position
new Handler().post(new Runnable() {
#Override
public void run() {
view.smoothScrollToPositionFromTop(position, 0);
}
});
}
getChildAtPosition()
public static View getChildAtPosition(final AdapterView view, final int position) {
final int index = position - view.getFirstVisiblePosition();
if ((index >= 0) && (index < view.getChildCount())) {
return view.getChildAt(index);
} else {
return null;
}
}
You should use setSelection() method.
Use LayoutManager to smooth scroll
layoutManager.smoothScrollToPosition(recyclerView, new RecyclerView.State(), position);
final Handler handler = new Handler();
//100ms wait to scroll to item after applying changes
handler.postDelayed(new Runnable() {
#Override
public void run() {
listView.smoothScrollToPosition(selectedPosition);
}}, 100);
The set selection method mentioned by Lars works, but the animation was too jumpy for our purposes as it skips whatever was left. Another solution is to recall the method repeatedly until the first visible position is your index. This is best done quickly and with a limit as it will fight the user scrolling the view otherwise.
private void DeterminedScrollTo(Android.Widget.ListView listView, int index, int attempts = 0) {
if (listView.FirstVisiblePosition != index && attempts < 10) {
attempts++;
listView.SmoothScrollToPositionFromTop (index, 1, 100);
listView.PostDelayed (() => {
DeterminedScrollTo (listView, index, attempts);
}, 100);
}
}
Solution is in C# via. Xamarin but should translate easily to Java.
Do you call arrayadapter.notifyDataSetChanged() after you called arrayadapter.add()? Also to be sure, smoothScrollToPosition and setSelection are methods available in ListView not arrayadapter as you have mentioned above.
In any case see if this helps:
smoothScrollToPosition after notifyDataSetChanged not working in android
Solution in kotlin:
fun AbsListView.scrollToIndex(index: Int, duration: Int = 150) {
smoothScrollToPositionFromTop(index, 0, duration)
postDelayed({
setSelection(index)
post { smoothScrollToPositionFromTop(index, 0, duration) }
}, duration.toLong())
}
PS: Looks like its quite messed up on Android SDK side so this is kind of best you can get, if you don't want to calculate your view offset manually. Maybe best easy way is to set duration to 0 for long list to avoid any visible jump.
I had some issues when calling just setSelection in some positions in GridView so this really seems to me as solution instead of using that.
use this in android java, it work for me:
private void DeterminedScrollTo(int index, int attempts) {
if (listView.getFirstVisiblePosition() != index && attempts < 10) {
attempts++;
if (listView.canScrollVertically(pos))
listView.smoothScrollToPositionFromTop(index, 1, 200);
int finalAttempts = attempts;
new Handler(Looper.getMainLooper()).postDelayed(new Runnable() {
#Override
public void run() {
DeterminedScrollTo(index, finalAttempts);
}
}, 200);
}
}
Related
I have a recyclerview with gridlayoutmanager.
If I run the code
recycler.smoothScrollTo(adapter.getItemCount())
the recycler scrolls really fast to the last element. I tried some solutions on Stackoverflow to make the scrolling slower, but all apply to Linearlayoutmanager not Gridlayoutmanager.
Any help?
I cannot say for sure what your problem is. But I am lucky enough to have a very simple GridLayoutManager recyclerview demo out there, very small sample project. I created a so branch and added a button that does the same you do.
Look it up: https://github.com/Gryzor/GridToShowAds/compare/so?expand=1
.setOnClickListener { mainRecyclerView.smoothScrollToPosition(data.size) }
And that alone just works.
Check the source code, it's a very simple sample for something unrelated, but happens to have a RV with a Grid Layout :)
UPDATE
What you actual want is to control the Speed at which the recyclerView scrolls. Ok.
It's not the RecyclerView that drives the scroll, it's actually the LayoutManager that does. How so?
If you look at RV's source code...
public void smoothScrollToPosition(int position) {
...
mLayout.smoothScrollToPosition(this, mState, position);
}
So it ends up calling mLayout. What is this?
#VisibleForTesting LayoutManager mLayout;
So, your LayoutManager#smoothScroll... method is used.
Decompiling now GridLayoutManager for science:
#Override
public void smoothScrollToPosition(RecyclerView recyclerView, RecyclerView.State state,
int position) {
LinearSmoothScroller linearSmoothScroller =
new LinearSmoothScroller(recyclerView.getContext());
linearSmoothScroller.setTargetPosition(position);
startSmoothScroll(linearSmoothScroller);
}
note: this method is actually in LinearLayoutManager because GridLayoutManager is a subclass and it doesn't override the method
A LinearSmoothScroller!; no parameter to specify the speed though...
Look at it:
public class LinearSmoothScroller extends RecyclerView.SmoothScroller {
private static final boolean DEBUG = false;
private static final float MILLISECONDS_PER_INCH = 25f;
private static final int TARGET_SEEK_SCROLL_DISTANCE_PX = 10000;
...
}
This class has a start() method described as:
* Starts a smooth scroll for the given target position.
So who calls this?
The mLayout.smoothScrollToPosition method does at the end in the startSmoothScroll(...) call.
public void startSmoothScroll(SmoothScroller smoothScroller) {
Starts a smooth scroll using the provided {#link SmoothScroller}.
mSmoothScroller.start(mRecyclerView, this);
So... in lieu of all this, the answer to your question is:
You need to create your extension of GridLayoutManager by subclassing it, and in it, override the smoothScrollToPosition method, to provide your own Scroller logic.
Thread carefully though, LayoutManagers are not the "simplest" classes of all time and they can be quite complicated to master.
Good luck! :)
My simple working solution currently is still implementing a timer then working with it.
final CountDownTimer scrollUp_timer = new CountDownTimer(50000, 30) {
#Override
public void onTick(long millisUntilFinished) {
if (layoutManager != null && layoutManager.findFirstVisibleItemPosition() != 0) searchRecyclerView.smoothScrollToPosition(layoutManager.findFirstVisibleItemPosition()-1);
}
#Override
public void onFinish() {
try{
}catch(Exception e){
// log
}
}
};
scrollUp.setOnDragListener(new View.OnDragListener() {
#Override
public boolean onDrag(View view, DragEvent dragEvent) {
layoutManager = ((GridLayoutManager)searchRecyclerView.getLayoutManager());
int action = dragEvent.getAction();
if (action == DragEvent.ACTION_DRAG_ENTERED) {
scrollUp_timer.start();
} else if (action == DragEvent.ACTION_DRAG_EXITED) {
searchRecyclerView.scrollBy(0,0);
scrollUp_timer.cancel();
}
return true;
}
});
You can extend:
class CSCustomRecyclerSmoothScroller(context: Context, speed: Float = 0.2f)
: LinearSmoothScroller(context) {
override fun calculateSpeedPerPixel(displayMetrics: DisplayMetrics): Float = speed
}
And use it like:
val shortAnimationDuration =
view.resources.getInteger(android.R.integer.config_shortAnimTime)
val scroller = CSCustomRecyclerSmoothScroller(this, speed = 0.15)
scroller.targetPosition = position
view.postDelayed({
layoutManager.startSmoothScroll(scroller)
}, shortAnimationDuration.toLong())
postDelayed can be necessary in some cases but maybe not in all.
I use similar code with GridLayoutManager I just tried to extract relevant parts from my way of writing things.
I'm working on a Circular ViewPager, and i've implemented this exactly solution (https://stackoverflow.com/a/12965787/1083564).
The only thing is missing, is the fact that i need to smoothScroll when i'm using the setCurrentItem(int i, bol b) method, that instantly goes to the pixel limit, without using the smoothScroll.
I already have the access to use this method, using the following code:
package android.support.v4.view;
import android.content.Context;
import android.util.AttributeSet;
public class MyViewPager extends ViewPager {
public MyViewPager(Context context) {
super(context);
}
public MyViewPager(Context context, AttributeSet attr) {
super(context, attr);
}
public void smoothScrollTo(int x, int y, int velocity) {
super.smoothScrollTo(x, y, velocity);
}
}
But i couldn't figure it out where and how to use it. I have the number of pixels that i need to run smoothly by using this code inside the setOnPageChangeListener on my ViewPager:
#Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
Log.d( "viewpager", positionOffsetPixels+"");
}
Before it goes to 0, instantly, because of the setCurrentItem, i have the value of pixels left to reach 0 (to the left) or x (to the right, depending of screen). I dont know how can i get this x number too.
PS: I think this solution is the exatcly one used by IMDB app. You can see this scrolling from the first to the last but one, without remove your finger (use 2 fingers to do it). You will see that the "white limit" will show from the left side of the ViewPager. The only difference is that they know how to smooth scroll after using the setCurrentItem.
If you need some more information, please, ask! Thanks!
Issue: When you detect circular scrolling has to be perfomed, calling setCurrentItem immediately will cause the ViewPager to scroll to the real fragment immediately without smooth scrolling as it is set to false.
Solution: Instead allow the ViewPager to scroll to the fake fragment smoothly as it does for other fragments and then scroll to the real fragment after some delay with smooth scrolling set to false. User will not notice the change.
When we are performing circular scrolling, call setCurrentItem in a runnable with some delay. Use onPageSelected to know the index of the page selected.
public void onPageSelected(int position) {
// Consider eg. : C' A B C A'
boolean circularScroll = false;
if(position == 0) {
// Position 0 is C', we need to scroll to real C which is at index 3.
position = mPager.getAdapter().getCount() - 2;
circularScroll = true;
}
int lastIndex = mPager.getAdapter().getCount() - 1;
if(position == lastIndex) {
// Last index is A', we need to scroll to real A, which is at index 1.
position = 1;
circularScroll = true;
}
if(circularScroll) {
final int realPosition = position;
mPager.postDelayed(new Runnable() {
#Override
public void run() {
mPager.setCurrentItem(realPosition, false);
}
}, 500L);
}
}
When you set the second parameter of the setCurrentItem to true it should smooth scroll
#Override
public void onPageScrollStateChanged (int state) {
if (state == ViewPager.SCROLL_STATE_IDLE) {
int curr = viewPager.getCurrentItem();
int lastReal = viewPager.getAdapter().getCount() - 2;
if (curr == 0) {
viewPager.setCurrentItem(lastReal, true);
} else if (curr > lastReal) {
viewPager.setCurrentItem(1, true);
}
}
}
This is my first ever post here and I'm a dumb novice, so I hope someone out there can both help me and excuse my ignorance.
I have a ListView which is populated with an ArrayAdapter. When I either scroll or click, I want the selected item, or the item nearest the vertical center, to be forced to the exact vertical center of the screen. If I call listView.setSelection(int position) it aligns the selected position at the top of the screen, so I need to use listView.setSelectionFromTop(position, offset) instead. To find my offset, I take half of the View's height from the half of the ListView's height.
So, I can vertically center my item easy enough, within OnItemClick or OnScrollStateChanged, with the following:
int x = listView.getHeight();
int y = listView.getChildAt(0).getHeight();
listView.setSelectionFromTop(myPosition, x/2 - y/2);
All this works fine. My problem is with the initial ListView setup. I want an item to be centered when the activity starts, but I can't because I get a NullPointerException from:
int y = listView.getChildAt(0).getHeight();
I understand this is because the ListView has not yet rendered, so it has no children, when I call this from OnCreate() or OnResume().
So my question is simply: how can I force my ListView to render at startup so I can get the height value I need? Or, alternatively, is there any other way to center items vertically within a ListView?
Thanks in advance for any help!
int y = listView.getChildAt(0).getHeight();
I understand this is because the ListView has not yet rendered, so it has no children, when I call this from onCreate() or onResume().
You should call it in onScroll.
listView.setOnScrollListener(new OnScrollListener() {
#Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
}
#Override
public void onScroll(AbsListView view, int firstVisibleItem,
int visibleItemCount, int totalItemCount) {
//Write your logic here
int y = listView.getChildAt(0).getHeight();
}
});
I'm answering my own question here, but it's very much a hack. I think it's interesting because it sheds some light on the behavior of listviews.
The problem was in trying to act on data (a listview row) that did not yet exist (it had not been rendered). listview.getChildAt(int) was null because the listview had no children yet. I found out onScroll() is called immediately when the activity is created, so I simply put everything in a thread and delayed the getChildAt() call. I then enclosed the whole thing in a boolean wrapper to make sure it is only ever called once (on startup).
The interesting thing was that I only had to delay the call by 1ms for everything to be OK. And that's too fast for the eye to see.
Like I said, this is all a hack so I'm sure all this is a bad idea. Thanks for any help!
private boolean listViewReady = false;
public void onScroll(AbsListView view, int firstVisibleItem,
int visibleItemCount, int totalItemCount) {
if (!listViewReady){
Thread timer = new Thread() {
public void run() {
try{
sleep(1);
}catch (InterruptedException e) {
e.printStackTrace();
}finally{
runOnUiThread(new Runnable() {
public void run() {
myPosition = 2;
int x = listView.getHeight();
int y = listView.getChildAt(0).getHeight();
listView.setSelectionFromTop(myPosition, x/2 - y/2);
listViewReady = true;
}
});
}
}
};
timer.start();
}//if !ListViewReady
I have achieved the same using a in my opinion slighlty simpler solution
mListView.post(new Runnable() {
#Override
public void run() {
int height = mListView.getHeight();
int itemHeight = mListView.getChildAt(0).getHeight();
if (positionOfMyItem == myCollection.size() - 1) {
// last element - > don't subtract item height
itemHeight = 0;
}
mListView.setSelectionFromTop(position, height / 2 - itemHeight / 2);
}
});
Scope
I need to scroll to certain position smoothly and then "jump" to another position with setSelection(anotherPosition). This is done to create an illusion of smooth scrolling of (e.g.) 100 items in ListView. smoothScrollToPosition(100) lasts too much, you know.
Problem
setSelection() doesn't wait till smoothScrollToPosition finishes its work, so setSelection() is being called immediately and user sees quick jumping only;
Code
private final int scrollableItems = 20;
int firstVisiblePosition = mListView.getFirstVisiblePosition();
if (firstVisiblePosition < scrollableItems) {
mListView.smoothScrollToPosition(0);
} else {
mListView.smoothScrollToPosition(firstVisiblePosition - scrollableItems);
mListView.setSelection(0);
}
mListView.clearFocus();
Idea
OK, we could change logic of smoothness illusion: first setSelection(), then scroll smoothly (we're scrolling to the very first item on top of the list):
int firstVisiblePosition = mListView.getFirstVisiblePosition();
if (firstVisiblePosition < scrollableItems) {
mListView.smoothScrollToPosition(0);
} else {
mListView.setSelection(scrollableItems);
mListView.smoothScrollToPosition(0);
}
mListView.clearFocus();
final ListView listView = ...;
View listItemView = ...;
listView.smoothScrollBy(listItemView.getHeight() * NUMBER_OF_VIEWS,
DURATION * 2);
listView.postDelayed(new Runnable() {
public void run() {
listView.smoothScrollBy(0, 0); // Stops the listview from overshooting.
listView.setSelection(0);
}
}, DURATION);
Of course, direction of the scroll etc. would need to be adjusted for your use case (go to the top of the list)
EDIT: Old solution could overshoot if the velocity of the scroll was too high, smoothScrollBy(0,0) will stop the smooth scrolling before setting the selection properly and immediately.
Another way is to add an OnScrollListener.
private final int scrollableItems = 20;
int firstVisiblePosition = mListView.getFirstVisiblePosition();
if (firstVisiblePosition < scrollableItems) {
mListView.smoothScrollToPosition(0);
} else {
mListView.setOnScrollListener(new AbsListView.OnScrollListener() {
#Override
public void onScrollStateChanged(AbsListView absListView, int i) {
if (i == SCROLL_STATE_IDLE) {
mListView.setSelection(0);
}
}
})
mListView.smoothScrollToPosition(firstVisiblePosition - scrollableItems);
}
mListView.clearFocus();
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.