Develop Reference

RecyclerView position will changed by receiving new data

I used notifyDataSetChanged in in my recycleriew. like this:
private void setList(List<Article> articles) {
mainList.addAll(articles);
notifyDataSetChanged();
}
But I want to use diffUtill in my recycleriew. I created my own diffUtill like this:
public class ArticleListDiffTool extends DiffUtil.Callback {
List<Article> oldList;
List<Article> newList;
private static final String TAG = "ArticleListDiffTool";
public ArticleListDiffTool(List<Article> oldList, List<Article> newList) {
this.oldList = oldList;
this.newList = newList;
Log.d(TAG, "ArticleListDiffTool: " + this.oldList.size() + "\n" + this.newList.size());
}
#Override
public int getOldListSize() {
return oldList.size();
}
#Override
public int getNewListSize() {
return newList.size();
}
#Override
public boolean areItemsTheSame(int oldItemPosition, int newItemPosition) {
return oldList.get(oldItemPosition).getId() .equals( newList.get(newItemPosition).getId());
}
#Override
public boolean areContentsTheSame(int oldItemPosition, int newItemPosition) {
return oldList.get(oldItemPosition).equals(newList.get(newItemPosition));
}
#Nullable
#Override
public Object getChangePayload(int oldItemPosition, int newItemPosition) {
//you can return particular field for changed item.
return super.getChangePayload(oldItemPosition, newItemPosition);
}
}
And I use it in my adapter :
private void setList(List articles) {
DiffUtil.DiffResult diffResult = DiffUtil.calculateDiff(new ArticleListDiffTool(this.mainList, articles),true);
mainList.addAll(articles);
diffResult.dispatchUpdatesTo(this);
}
I want to add new data to my old list. But when new data received, the recyclerView will be scrolled to the top of the list.
But I want to recyclerView be in its user state and new data add to the rest of the old list.

RecylcerView updates knows nothing about your views. When you call notifyDataSetChanged it tries to determine which views moved, or were replaced. I don't see you using setHasStableIds so when calling notifyDataSetChanged it will assume all of the content was replaced. It will jump to position 0 and be done with it. When you use setHasStableIds it will check the ids of the visible items and update the content in them. It will stop jumping around.
Now you also show that you are using DiffUtil. This is great! When you're not working with setHasStableIds this is the way to properly tell the recyclerView about what changed.
The problem you are facing is that you're using both. Either move to long ids and let the recyclerview do the diffing itself, or use DiffUtil and remove the call to notifyDataSetChanged. Either variant should work.

If you add new items at the end of the recyclerview, before you add the data, store the 1st visible item in recyclerview:
int position = ((LinearLayoutManager) recyclerView.GetLayoutManager()).findFirstVisibleItemPosition();
and after you make all the changes and call notifyDatasetChanged() scroll to position:
recyclerView.scrollToPosition(position);

I Found the problem after a few hours.
I every time that wants to update my recyclerView send received data to my adapter
And DiffUtil goes to compare my old list with received new parts and because of that (completely new items) DiffUtil decides to refresh whole recyclerView list.
Solution:
Now I get the current list from the recyclerView adapter and use addAll to insert new items that received from the server, then I pass this complete list to the adapter.
Now DiffUtil can compare diffrent between my old and new lists and recyclerView will be stay at it's current position.

How to reset recyclerView position item views to original state after refreshing adapter

I have a RecyclerView with rows that have views that when clicked will be disabled for that row position.
The problem is after I update the adapter like this:
adapterData.clear();
adapterData.addAll(refreshedAdapterData);
notifyDataSetChanged();
After refreshing the data, the disabled views at the previous recycler position still remain disabled even though the data is refreshed.
How can I reset the views to the original state after refreshing adapter data.

Use below code.
adapterData.clear();
adapterData.addAll(refreshedAdapterData);
adapter.notifyDataSetChanged();
OR
recyclerView.invalidate();

When you call notifyDataSetChanged(), the onBindViewHolder() method of every view is called. So you could add something like this in the onBindViewHolder() of your Adapter method:
#Override
public void onBindViewHolder(final RecyclerView.ViewHolder viewHolder, final int position) {
if (refreshedAdapterData.get(position).isInDefaultState()) {
//set Default View Values
} else {
//the code you already have
}
}

I have resolved this by putting a conditional statement inside onBindViewHolder method instructing all positions to reset the disabled views if data meets the required conditions for a refreshed data.
#Christoph Mayr, thanks for your comments. It helped point me in the right direction.

I cleared the data then notify change but the selected checkbox doesn't reset but just moves up one position. Let say I selected item #1 , move out of the RecyclerView, came back and it will auto select item #0.
So, I created new adapter again at onResume(), i worked for me but i don't know if it's the right way to handle this situation.
#Override
public void onResume() {
super.onResume();
if(selectedItems != null && selectedItems.size() > 0){
selectedItems.clear(); // if no selected items before then no need to reset anything
if(adapter != null && recyclerView != null){
// to remove the checked box
adapter = null;
adapter = new MyAdapter(items, new MyAdapter.MyAdapterListener() {
#Override
public void onSelected(int pos) {
selectedItems.add(items.get(pos));
}
#Override
public void onUnSelected(int pos) {
selectedItems.remove(items.get(pos));
}
});
recyclerView.setAdapter(adapter);
}
}
}

RecyclerView scroll in incorrect direction when new element is inserted

I use smoothScrollToPosition to scroll RecyclerView. It does scroll every time a new entry is inserted; but to the top, not to the bottom, which is the direction i want.
list_chat = (RecyclerView) findViewById(R.id.list_chat);
//Set up Layout Manager
linearLayoutManager = new LinearLayoutManager(this);
linearLayoutManager.setStackFromEnd(true);
list_chat.setLayoutManager(linearLayoutManager);
//set adapter
list_chat.setAdapter(adapter);
//set scroll
list_chat.post(new Runnable() {
#Override
public void run() {
list_chat.smoothScrollToPosition(adapter.getItemCount());
}
});
The adapter is from Firebase
adapter = new FirebaseRecyclerAdapter<ChatItem, ChatRecylerViewHolder>(ChatItem.class,R.layout.chat_item
,ChatRecylerViewHolder.class,queryChat ) {
#Override
protected void populateViewHolder(ChatRecylerViewHolder viewHolder, ChatItem model, int position) {
viewHolder.tvAuthorChat.setText(model.chatAuthor);
viewHolder.tvContentChat.setText(model.chatContent);
}
};

You do notice you are using linearLayoutManager.setStackFromEnd(true); this mean you first position is at the bottom. I suggest you a better option.
RecycleView didn't work the way listView work, you can scroll it with your layout manager something like this
linearLayoutManager.scrollToPositionWithOffset(position,offset);
Which position is the position you want to scroll to, offset is the offset within the current position. You could just use with one parameter as well.
linearLayoutManager.scrollToPosition(position);

Ok. I found the answer.
First, the old problem with my question: i thought list_chat.post is called whenever an item is inserted (turn out that is wrong). The reason for it keeps scrolling top is linearLayoutManager.setStackFromEnd(true);
Thus, the question comes down to Where to call the scrolling ?
The answer is : Since adapter manages data, it makes sense to guess that adapter will notify the insertion.
Here is the code
adapter.registerAdapterDataObserver(new RecyclerView.AdapterDataObserver() {
#Override
public void onItemRangeInserted(int positionStart, int itemCount) {
super.onItemRangeInserted(positionStart, itemCount);
list_chat.smoothScrollToPosition(adapter.getItemCount());
}
});

Is there a callback for when RecyclerView has finished showing its items after I've set it with an adapter?

Background
I've made a library that shows a fast-scroller for RecyclerView (here, in case anyone wants), and I want to decide when to show and when to hide the fast-scroller.
I think a nice decision would be that if there are items that aren't shown on the screen (or there are a lot of them that do not appear), after the RecyclerView finished its layout process, I would set the fast-scroller to be visible, and if all items are already shown, there is no need for it to be shown.
The problem
I can't find a listener/callback for the RecyclerView, to tell me when it has finished showing items, so that I could check how many items are shown compared to the items count.
The recyclerView might also change its size when the keyboard appears and hides itself.
What I've tried
The scrolling listener will probably not help, as it occurs "all the time", and I just need to check only when the RecyclerView has changed its size or when the items count (or data) has changed.
I could wrap the RecyclerView with a layout that notifies me of size changes, like this one that I've made, but I don't think it will work as the RecyclerView probably won't be ready yet to tell how many items are visible.
The way to check the number of items being shown might be used as such:
final LinearLayoutManager layoutManager = new LinearLayoutManager(getActivity(), LinearLayoutManager.VERTICAL, false);
mRecyclerView.setLayoutManager(layoutManager);
...
Log.d("AppLog", "visible items count:" + (layoutManager.findLastVisibleItemPosition() -layoutManager.findFirstVisibleItemPosition()+1));
The question
How do I get notified when the recyclerView has finished showing its child views, so that I could decide based on what's currently shown, to show/hide the fast-scroller ?

I've found a way to solve this (thanks to user pskink), by using the callback of LayoutManager:
final LinearLayoutManager layoutManager = new LinearLayoutManager(getActivity(), LinearLayoutManager.VERTICAL, false) {
#Override
public void onLayoutChildren(final Recycler recycler, final State state) {
super.onLayoutChildren(recycler, state);
//TODO if the items are filtered, considered hiding the fast scroller here
final int firstVisibleItemPosition = findFirstVisibleItemPosition();
if (firstVisibleItemPosition != 0) {
// this avoids trying to handle un-needed calls
if (firstVisibleItemPosition == -1)
//not initialized, or no items shown, so hide fast-scroller
mFastScroller.setVisibility(View.GONE);
return;
}
final int lastVisibleItemPosition = findLastVisibleItemPosition();
int itemsShown = lastVisibleItemPosition - firstVisibleItemPosition + 1;
//if all items are shown, hide the fast-scroller
mFastScroller.setVisibility(mAdapter.getItemCount() > itemsShown ? View.VISIBLE : View.GONE);
}
};
The good thing here is that it works well and will handle even keyboard being shown/hidden.
The bad thing is that it gets called on cases that aren't interesting (meaning it has false positives), but it's not as often as scrolling events, so it's good enough for me.
EDIT: there is a better callback that was added later, which doesn't get called multiple times. Here's the new code instead of what I wrote above:
recyclerView.setLayoutManager(new LinearLayoutManager(getActivity(), LinearLayoutManager.VERTICAL, false) {
#Override
public void onLayoutCompleted(final State state) {
super.onLayoutCompleted(state);
final int firstVisibleItemPosition = findFirstVisibleItemPosition();
final int lastVisibleItemPosition = findLastVisibleItemPosition();
int itemsShown = lastVisibleItemPosition - firstVisibleItemPosition + 1;
//if all items are shown, hide the fast-scroller
fastScroller.setVisibility(adapter.getItemCount() > itemsShown ? View.VISIBLE : View.GONE);
}
});

I'm using the 'addOnGlobalLayoutListener' for this. Here is my example:
Definition of an interface to perform the action required after the load:
public interface RecyclerViewReadyCallback {
void onLayoutReady();
}
on the RecyclerView, I trigger the onLayoutReady method when the load is ready:
mRecyclerView.getViewTreeObserver().addOnGlobalLayoutListener(() -> {
if (recyclerViewReadyCallback != null) {
recyclerViewReadyCallback.onLayoutReady();
}
recyclerViewReadyCallback = null;
});
Note: The set to null is necessary to prevent the method from being called multiple times.

Leaving this here as an alternate approach. Might be useful in some cases. You can also make use of the LinearLayoutManagers onScrollStateChanged() and check when the scroll is idle.
One thing to remember, when you load your view for the 1st time, this will not be called, only when the user starts scrolling and the scroll completes, will this be triggered.
LinearLayoutManager layoutManager = new LinearLayoutManager(getContext(),
RecyclerView.HORIZONTAL, false) {
#Override
public void onScrollStateChanged(int state) {
super.onScrollStateChanged(state);
if (state == RecyclerView.SCROLL_STATE_IDLE) {
// your logic goes here
}
}
}
};

The solution that works for me. Needed to do some stuff after RecyclerView was inited with items.
adapter.registerAdapterDataObserver(object : RecyclerView.AdapterDataObserver() {
override fun onChanged() {
viewModel.onListReady()
adapter.unregisterAdapterDataObserver(this)
}
})

RecyclerView StaggeredGridLayoutManager reordering issue

I'm trying to display three (at least that's the case I have an issue with) items in a RecyclerView with a StaggeredGridLayoutManager with two columns. The first item is spanned across the two rows. Here's how it looks like:
Now, I'm moving the item "Item 2" to top. Here's the code I call, in the adapter (it's a sample I wrote to demonstrate the issue I have in a more complex project):
private int findById(int id) {
for (int i = 0; i < items.size(); ++i) {
if (items.get(i).title.equals("Item " + id)) {
return i;
}
}
return -1;
}
// Moving the item "Item 2" with id = 2 and position = 0
public void moveItem(int id, int position) {
final int idx = findById(id);
final Item item = items.get(idx);
if (position != idx) {
items.remove(idx);
items.add(position, item);
notifyItemMoved(idx, position);
//notifyDataSetChanged();
}
}
After that, the array is fine: [Item 2, Item 1, Item 3]. However, the view is far from fine:
If I touch the RecyclerView (enough to trigger the overscroll effect if there's not enough items to scroll), Item 2 move to the left, where I expected to see it in the first place (with a nice animation):
As you maybe saw in the code, I tried to replace notifyItemMoved(idx, position) by a call to notifyDataSetChanged(). It works, but the change is not animated.
I wrote a complete sample to demonstrate this and put it on GitHub. It's nearly minimal (there are options to move the item and toggle their spanning).
I don't see what I can be doing wrong. Is this a bug with StaggeredGridLayoutManager? I would like to avoid notifyDataSetChanged() as I would like to keep consistency regarding the animations.
Edit: after some digging, there's no need for a fully-spanned item to show the issue. I removed the full-span. When I try to move Item 2 to position 0, it doesn't move: Item 1 goes after it, and Item 3 is moved on the right, so I have: empty cell, Item 2, new line, Item 1, Item 3. I still have the correct layout after a scroll.
What's more interesting is that I don't have the issue with a GridLayoutManager. I need a full-span item so it's not a solution, but I guess it's indeed a bug in the StaggeredGridLayoutManager…

I don't have a complete answer, but I can point you to both a workaround and the bug report (that I believe is related).
The trick to updating the layout so that it looks like your second screenshot, is to call invalidateSpanAssignments() on the StaggeredGridLayoutManger (sglm) after you've called notifyItemMoved(). The "challenge" is that if you call it immediately after nIM(), it won't run. If you delay the call for a few ms, it will. So, in your referenced code for MainActivity, I've made your sglm a private field:
private StaggeredGridLayoutManager sglm;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
adapter = new Adapter();
recyclerView = (RecyclerView) findViewById(R.id.recycler_view);
sglm = new StaggeredGridLayoutManager(2, StaggeredGridLayoutManager.VERTICAL);
recyclerView.setLayoutManager(sglm);
recyclerView.setItemAnimator(new DefaultItemAnimator());
recyclerView.setAdapter(adapter);
}
And down in the switch block, reference it in a handler:
case R.id.move_sec_top:
adapter.moveItem(2, 0);
new Handler().postDelayed(new Runnable() {
#Override
public void run() {
sglm.invalidateSpanAssignments();
}
}, 100);
return true;
The result is that your animation still runs, the layout ends up the way you want it. This is a real kludge, but it does work. I believe this is the same bug that I found and reported at the following link:
https://code.google.com/p/android/issues/detail?id=93156
While my "symptom" and required call were different, the underlying issue seems to be identical.
Good luck!
EDIT: No need to postDelayed, simply posting will do the trick:
case R.id.move_sec_top:
adapter.moveItem(2, 0);
new Handler().post(new Runnable() {
#Override
public void run() {
sglm.invalidateSpanAssignments();
}
});
return true;
My original theory was that the call was blocked until the layout pass was over, but I believe that is not the case. Instead, I now think that if you call invalidateSpanAssignments() immediately, it actually executes too soon (before the layout changes have completed). So, the post above (without delay) simply adds the call to the end of the rendering queue where it happens after the layout.

Well I have done this way.
StaggeredGridLayoutManager gaggeredGridLayoutManager = new StaggeredGridLayoutManager(2, StaggeredGridLayoutManager.VERTICAL);
gaggeredGridLayoutManager.setGapStrategy(StaggeredGridLayoutManager.GAP_HANDLING_MOVE_ITEMS_BETWEEN_SPANS);
recyclerView.setLayoutManager(gaggeredGridLayoutManager);
dataList = YourDataList (Your Code for Arraylist);
recyclerView.setItemAnimator(new DefaultItemAnimator());
recyclerAdapter = new DataAdapter(dataList, recyclerView);
recyclerView.setAdapter(recyclerAdapter);
// Magic line
recyclerView.addOnScrollListener(new ScrollListener());
Create class for Custom RecyclerView Scroll Listener.
private class ScrollListener extends RecyclerView.OnScrollListener {
#Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
gaggeredGridLayoutManager.invalidateSpanAssignments();
}
}
Hope this will help you.