Background
I work on an app that has a RecyclerView which you can scroll up and down however you wish.
The data items are loaded from the server, so if you are about to reach the bottom or the top, the app gets new data to show there.
To avoid weird scrolling behavior, and staying on the current item, I use 'DiffUtil.Callback' , overriding 'getOldListSize', 'getNewListSize', 'areItemsTheSame', 'areContentsTheSame'.
I've asked about this here, since all I get from the server is a whole new list of items, and not the difference with the previous list.
The problem
The RecyclerView doesn't have only data to show. There are some special items in it too:
Since Internet connection might be slow, there is a header item and a footer item in this RecyclerView, which just have a special Progress view, to show you've reached the edge and that it will get loaded soon.
The header and footer always exist in the list, and they are not received from the server. It's purely a part of the UI, just to show things are about to be loaded.
Thing is, just like the other items, it needs to be handled by DiffUtil.Callback, so for both areItemsTheSame and areContentsTheSame, I just return true if the old header is the new header, and the old footer is the new footer:
override fun areItemsTheSame(oldItemPosition: Int, newItemPosition: Int): Boolean {
val oldItem = oldItems[oldItemPosition]
val newItem = newItems[newItemPosition]
when {
oldItem.itemType != newItem.itemType -> return false
oldItem.itemType == ItemType.TYPE_FOOTER || oldItem.itemType == AgendaItem.TYPE_HEADER -> return true
...
}
}
override fun areContentsTheSame(oldItemPosition: Int, newItemPosition: Int): Boolean {
val oldItem = oldItems[oldItemPosition]
val newItem = newItems[newItemPosition]
return when {
oldItem.itemType == ItemType.TYPE_FOOTER || oldItem.itemType == ItemType.TYPE_HEADER -> true
...
}
}
}
Seems right? Well it's wrong. If the user is at the top of the list, showing the header, and the list gets updated with new items, the header will stay at the top, meaning the previous items you've seen will get pushed away by the new ones.
Example:
Before: header, 0, 1, 2, 3, footer
After: header, -3, -2, -1, 0, 1, 2, 3, footer
So if you stayed on the header, and the server sent you the new list, you still see the header, and below the new items, without seeing the old ones. It scrolls for you instead of staying on the same position .
Here's a sketch showing the issue. The black rectangle shows the visible part of the list.
As you can see, before loading, the visible part has the header and some items, and after loading it still has the header and some items, but those are new items that pushed away the old ones.
I need the header to be gone on this case, because the real content is below it. Instead of the area of the header, it might show other items (or a part of them) above it, but the visible position of the current items should stay where they are.
This issue only occurs when the header is shown, at the top of the list. In all other cases it works fine, because only normal items are shown at the top of the visible area.
What I've tried
I tried to find how to set DiffUtil.Callback to ignore some items, but I don't think such a thing exists.
I was thinking of some workarounds, but each has its own disadvantages:
A NestedScrollView (or RecyclerView) which will hold the header&footer and the RecyclerView in the middle, but this might cause some scrolling issues, especially due to the fact I already have a complex layout that depends on the RecyclerView (collapsing of views etc...).
Maybe in the layout of the normal items, I could put the layout of the header and footer too (or just the header, because this one is the problematic one). But this is a bad thing for performance as it inflates extra views for nothing. Plus it requires me to toggle hiding and viewing of the new views within.
I could set a new ID for the header each time there is an update from the server, making it as if the previous header is gone, and there is a totally new header at the top of the new list. However, this might be risky in the case of no real updates of the list at the top, because the header will be shown as if it's removed and then re-added.
The questions
Is there a way to solve this without such workarounds?
Is there a way to tell DiffUtil.Callback : "these items (header&footer) are not real items to scroll to, and these items (the real data items) should be" ?
I will try to explain what I see as a solution to your problem:
Step 1: Remove all the code for FOOTER and HEADER views.
Step 2: Add these methods that add and remove dummy model items in adapter based on the user scroll direction:
/**
* Adds loader item in the adapter based on the given boolean.
*/
public void addLoader(boolean isHeader) {
if (!isLoading()) {
ArrayList<Model> dataList = new ArrayList<>(this.oldDataList);
if(isHeader) {
questions.add(0, getProgressModel());
else {
questions.add(getProgressModel());
setData(dataList);
}
}
/**
* Removes loader item from the UI.
*/
public void removeLoader() {
if (isLoading() && !dataList.isEmpty()) {
ArrayList<Model> dataList = new ArrayList<>(this.oldDataList);
dataList.remove(getDummyModel());
setData(questions);
}
}
public MessageDetail getChatItem() {
return new Model(0, 0, 0, "", "", "")); // Here the first value is id which is set as zero.
}
And here is your rest of the adapter logic that you need to decide if the item is a loader item or an actual data item:
#Override
public int getItemViewType(int position) {
return dataList.get(position).getId() == 0 ? StaticConstants.ItemViewTypes.PROGRESS : StaticConstants.ItemViewTypes.CONTENT;
}
According to the view type, you can add a progress bar view holder in your adapter.
Step 3: use these methods in data loading logic:
While making the API call in onScrolled() method of recyclerView, you need to add a loader item before the api call and then remove it after the api call. Use the given adapter methods above. The coded in onScrolled should look a little like this:
recyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
#Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
if (dy < 0) { //This is top scroll, so add a loader as the header.
recyclerViewAdapter.addLoader(true);
LinearLayoutManager linearLayoutManager = (LinearLayoutManager) recyclerView.getLayoutManager();
if (!recyclerViewAdapter.isLoading(true)) {
if (linearLayoutManager.findFirstCompletelyVisibleItemPosition() <= 2) {
callFetchDataApi();
}
}
}
} else {
if (!recyclerViewAdapter.isLoading(false)) {
if (linearLayoutManager.findLastCompletelyVisibleItemPosition() >= linearLayoutManager.getItemCount() - 2) {
callFetchDataApi();
}
}
});
Now after the api call gives you the data you need. Simply remove the added loader from the list like this:
private void onGeneralApiSuccess(ResponseModel responseModel) {
myStreamsDashboardAdapter.removeLoader();
if (responseModel.getStatus().equals(SUCCESS)) {
// Manage your pagination and other data loading logic here.
dataList.addAll(responseModel.getDataList());
recyclerViewAdapter.setData(dataList);
}
}
And lastly, you need to avoid any scroll during data loading operation is add a logic method for that is isLoading() method. which is used in the code of method onScrolled():
public boolean isLoading(boolean isFromHeader) {
if (isFromHeader) {
return dataList.isEmpty() || dataList.get(0).getId() == 0;
} else {
return dataList.isEmpty() || dataList.get(dataList.size() -1).getId() == 0;
}
}
Let me know if you don't understand any of this.
I think for now, the solution I took will suffice. It's a bit weird, but I think it should work:
The header item gets a new id each time the list is different in its first real item. The footer always have the same id, because it's ok for it to move in the current way it works. I don't even need to check that its id is the same. The check of areItemsTheSame is as such for them:
oldItem.agendaItemType == AgendaItem.TYPE_HEADER -> return oldItem.id == newItem.id
oldItem.agendaItemType == AgendaItem.TYPE_FOOTER -> return true
This way, if the header belongs to a new list data, old one will be removed, and new one will be at the top.
It's not the perfect solution, as it doesn't really push the original header to be at the top, and theoretically it makes us "kinda" have 2 headers at the same time (one being removed and one being added) but I think it's good enough.
Also, for some reason, I can't use notifyItemChanged on the header and footer in case only they get updated (internet connection changes its state, so need to change the header&footer alone). Only notifyDataSetChanged works for some reason.
Still, if there is a more official way, could be nice to know.
I'm working on a note taking app. I add a note, and it get's added to the bottom of the list. As the last assertion in the espresso test, I want to make sure that the ListView displays a listItem that has just been added. This would mean grabbing the last item in the listView. I guess you might be able to do it in other ways? (e.g. get the size of adapted data, and go to THAT position? maybe?), but the last position of the list seems easy, but I haven't been able to do it. Any ideas?
I've tried this solution, but Espresso seems to hang. http://www.gilvegliach.it/?id=1
1. Find the number of elements in listView's adapter and save it in some variable. We assume the adapter has been fully loaded till now.:
final int[] numberOfAdapterItems = new int[1];
onView(withId(R.id.some_list_view)).check(matches(new TypeSafeMatcher<View>() {
#Override
public boolean matchesSafely(View view) {
ListView listView = (ListView) view;
//here we assume the adapter has been fully loaded already
numberOfAdapterItems[0] = listView.getAdapter().getCount();
return true;
}
#Override
public void describeTo(Description description) {
}
}));
2. Then, knowing the total number of elements in listView's adapter you can scroll to the last element:
onData(anything()).inAdapterView(withId(R.id.some_list_view)).getPosition(numberOfAdapterItems[0] - 1).perform(scrollTo())
In my app I am using recycler view.I want to show and hide view on particular condition.But when I scroll recycler views I am not getting expected behaviour.When I Visible a view it gets visible for other rows as well randomly.
What I understand is when it recycles it reuses view and when previous view when it gets recycled it finds the visibility of that view.How can I hide view on particular condition? here is my adapter code
#Override
public void onBindViewHolder(UrduRhymesViewHolder holder, int position) {
RhymesModel current = mUrduRhymesList.get(position);
AppUtility.setCustomFont(mContext, holder.tvUrduRhymesName, Constants.HANDLEE_REGULAR);
holder.tvUrduRhymesName.setText(current.getRhymeName());
holder.ivUrduRhymesLogo.setImageUrl(current.getThumbnailUrl(), mImageRequest);
int status = AppUtility.getFavouriteStatus(mContext, current.getRhymeName(), new UrduRhymesDb(mContext));
if (status == 0)
holder.btnFavourite.setBackgroundResource(R.mipmap.btn_star_unactive);
else
holder.btnFavourite.setBackgroundResource(R.mipmap.btn_star);
ProgressbarDetails progressbarDetails = ProgressbarDetails.getProgressDetail(current.getRhymeName());
if (progressbarDetails == null) {
progressbarDetails = new ProgressbarDetails();
progressbarDetails.prgProgressBar = holder.pbRhymeDownload;
progressbarDetails.download_btn_settings = holder.downloadButtonLayout;
} else {
progressbarDetails.prgProgressBar = holder.pbRhymeDownload;
progressbarDetails.download_btn_settings = holder.downloadButtonLayout;
holder.pbRhymeDownload.setProgress(progressbarDetails.progress);
}
ProgressbarDetails.addUpdateProgressDetail(current.getRhymeName(), progressbarDetails);
if (progressbarDetails != null && progressbarDetails.isDownloading) {
Log.e("test","downloading foe position "+position );
holder.downloadButtonLayout.setBackgroundResource(R.mipmap.btn_download);
holder.pbRhymeDownload.setVisibility(View.VISIBLE);
holder.pbRhymeDownload.setProgress(progressbarDetails.progress);
} else {
Log.e("test","should not be visible for position "+position);
holder.pbRhymeDownload.setVisibility(View.GONE);
}
}
Here progressbarDetails.isDownloading (having value true) is the criteria when I want to show my view but is else clause it is not hiding my view
Edit: Here ProgressbarDetails (Singleton )is a class keeping reference of every row of adapter's progress bar.
No direct way of hiding and unhiding recylerview childitems.
Solution:
Let us assume that the recyclerview adapter is ArrayList
Now make another arraylist (temp_list)
Scenarios:
Hide: iterate through your adapter items and remove the ones that you want to hide. Put each of these into temp_list. After iteration is over, call notifyDataSetChanged()
Show: iterate through your temp_list items and remove the ones that you want to show. Put each of these into adapter. After iteration is over, call notifyDataSetChanged()
You should add a flag in your viewHolder that indicates if this view should be displayed or not . and check this flag every time in the onBindViewHolder.
because the recyclerView reuses the same views you should make a decision depending on something special for every view in you viewHolder.
do u mean when your data has been changed?
and your layout want to change ?
adapter.notifyDataSetChanged();
I am writing an android app which contains a listview with some items (fetch by database, can be 100+)
i would like the scroll the listview to display the specific item (let say position x in the listview)
i used
listView.post(new Runnable() {
#Override
public void run() {
listView.smoothScrollToPosition(position);
}
});
the view has scrolled. but it stopped once the item appear. (the item is now displayed at the bottom of the screen)
i think better design is to display the item at the top of the screen or at least at the middle of the screen.
How can i do this?
I am now finding the way to find out the index of the listview which is really visible in the screen.
I have tried getFirstVisiblePosition() but it seems always return 0.
You will find setSelection() works better than smoothScrollToPosition(). If you are loading the data backing the ListView in the background, you will want to delay issuing the setSelection() until the data has been loaded.
getFirstVisiblePosition() works fine for me, but again is only useful once all the data has been loaded. Here is some code I use for a ListView that displays data fetched from a remote site:
// the list has been updated, fix the selection. loadFinished will be true if there are no phantom placeholders left.
protected void listLoaded(boolean loadFinished) {
// if the user has scrolled or we previously completed resetting the position, do nothing
if(wasScrolled)
return;
// if we were restored from saved data, reload that data now.
if(listState != null) {
postListView.onRestoreInstanceState(listState);
listState = null;
} else if(initialPos >= 0) // if we had a specific initial position, set it now
setSelection(initialPos);
else if(postId >= 0) // or if there is a specific post ID we want displayed
setSelection(postAdapter.getPostPosition(postId));
else // otherwise scroll to the first unread post
setSelection(postAdapter.getFirstUnread());
if(loadFinished) // if all data has been loaded, set a flag to prevent this being repeated
wasScrolled = true;
}
I'm trying to implement paging in a custom ListAdapter. Right now I'm just making the request for the next page when the last item in the ListView becomes visible, by checking in getView() if position is >= the size of ListAdapter.getCount().
It works fine, but I'm wondering if there's a better way (or a different way) that will only make the request once the last item in the list is actually visible to the user. Anyone know of a way?
I'm doing it almost the same way:
public static final int SCROLLING_OFFSET = 5;
// ...
private final ArrayList<T> items = new ArrayList<T>();
// ...
if (SCROLLING_OFFSET == items.size() - position) {
if (hasNextPage()) {
addNextPage();
}
}
private boolean hasNextPage() {
// basically calculates whether the last 2 pages contained the same # of items
}
private void addNextPage() {
// show spinner
// fetch next page in a background thread
// add to items
notifyDataSetChanged();
}
I think there is a better way to do it. Implementing the OnScrollListener interface. Take a look at this: Endless Scrolling ListView
Try removing the check altogether. In my experience, getView() is only called when the entry is about to come on screen.