I can get a total number of records from the server, so I am using PositionalDataSource for Network call. Everything works well but one problem: even if I don't scroll, the paging library continues fetching all the data from the server. How to solve this problem?
Using: androidx.paging:paging-runtime-ktx:2.1.1
Example:
override fun loadInitial(params: LoadInitialParams, callback: LoadInitialCallback<Doctor>) {
fetchDataFromApi(params.requestedStartPosition, params.pageSize) { list, totalCount ->
callback.onResult(list, 0, totalCount)
}
}
override fun loadRange(params: LoadRangeParams, callback: LoadRangeCallback<Doctor>) {
fetchDataFromApi(params.startPosition, params.loadSize) { list, totalCount ->
callback.onResult(list)
}
}
PagedList.Config.Builder()
.setPageSize(14)
.setPrefetchDistance(4)
.setInitialLoadSizeHint(14)
.setEnablePlaceholders(true)
.build()
It sounds like a similar issue I spend the last two days looking into. For me it turned out, that I had wrapped my RecyclerView inside a NestedScrollView.
However, the pagination library doesn't have built-in support for that according to this issue on Google tracker.
when you put recyclerview inside an infinite scrolling parent, it will layout all of its children because the parent provides infinite dimensions.
Basically the NestedScrollView continues triggering fetching more data as if the screen is as long as the complete list
Two options if this is the case for your case too:
Change your layout setup to not need the NestedScrollView
Here is a code example gist that helped me create a custom [SmartNestedScrollView]. Note that you have to set android:fillViewport="true" as well on this custom container and update the RecyclerView to have a height of wrap_content and remove the nestedScrollingEnabled flag from it.
Related
Problem Statement: Using Paging3 library and need to show loading information in header when user swipes to refresh. I followed the sample provided in the here.
Solution: Tried adding refresh header in LoadStateAdapter for with using pagingAdapter.withLoadStateHeaderAndFooter().
messagesRecyclerView.adapter = messagesAdapter.withLoadStateHeaderAndFooter(
header = MessageHeaderStateAdapter(messagesAdapter),
footer = MessageLoadStateAdapter()
)
But it does not shows the header until I swipe it 5-6 times in quick successions.
Footer, on other hand, shows just fine with loading more and error layouts based on LoadState.
Error State
Loading More State
Any pointers as to how this can be achieved are much appreciated.
withLoadStateHeader just returns a ConcatAdapter that listens to PREPEND state. If you want the header to show up during REFRESH you can basically copy the code out of that helper, but instead update LoadStateAdapter based on REFRESH LoadState using a listener on your PagingDataAdapter
val header = MyLoadStateHeader()
adapter.addLoadStateListener { loadStates ->
header.loadState = loadStates.refresh
}
recyclerView.adapter = ConcatAdapter(header, this)
I'm making an API call getData(forPage: Int): Response which returns a page-worth of data (10 items max) and thereIsMoreData: Boolean.
The recyclerView is implemented that by scrolling, the scroll listener automatically fetches more data using that API call:
val scrollListener = object : MyScrollListener() {
override fun loadMoreItems() {
apiFunctionForLoading(currentPage + 1)
}
}
The problem is that with longer screen devices that have more space for items (let's say 20), the RV receives 10 items and then doesn't allow scrolling, because there's no more items to scroll to. Without scrolling, more data cannot be loaded.
My naive solution:
load first set of data
if thereIsMoreData == true I load another page of data
now I have more data than the screen can display at once hence allowing scroll
Is there a more ellegant solution?
Android has this Paging Library now which is about displaying chunks of data and fetching more when needed. I haven't used it and it looks like it might be a bit of work, but maybe it's worth a look?
Codepath has a tutorial on using it and I think their stuff is pretty good and easy to follow, so maybe check that out too. They also have this older tutorial that's closer to what you're doing (handling it yourself) so there's that too.
I guess in general, you'd want your adapter to return an "infinite" number for getItemCount() (like Integer.MAX_VALUE). And then in your onBindViewHolder(holder, position) method you'd either set the item at position, or if you don't have that item yet you load in the next page until you get it.
That way your initial page will always have the right amount of content, because it will be full of ViewHolders that have asked for data - if there's more than 10, then item 11 will have triggered the API call. But actually handling the callback and all the updating is the tricky part! If you have that working already then great, but it's what the Paging library was built to take care of for you (or at least make it easier!)
An elegant way would be to check whether the view can actually scroll down:
recyclerView.canScrollVertically(1)
1 means downwards -> returns true if it is possible tro scroll down.
So if it returns false, your page is not fully filled yet.
I have a list of articles and when new articles appear on the server, I display the button informing user about that. When user clicks this button I want to load newest articles and add them to beginning of the list. While new articles are loading, I am displaying placeholder items (view skeletons of article item without data) for them in the RecyclerView and I scroll to top of the list so newest articles are visible.
The problem is that when new articles are fetched and they replace placeholders, the RecyclerView is not scrolled to the top but instead is scrolled on previous data and I have to manually scroll to be at the top of the list.
This has probably something to do with attempt of RecyclerView to keep user scrolled where he was before, but in this case, user was not here.
The workaround around this is either disable animations on RecyclerView or to not make diff of the data using DiffUtil but call notifyDatasetChanged.
I went with the second approach because I want to have animations
I have created a showcase repository demonstrating this problem. There are two Activities, one with vanilla RecyclerView and RecyclerView.Adapter and second one using epoxy library.
The code for the whole class is pretty complicated and I am not sure which is more relevant so this is how the whole Activity looks. She simulation of loading new articles
private fun simulateFetchNewArticles() {
scope.launch {
val newArticlesCount = 10
adapter.items = (0 until newArticlesCount).map { Item.Placeholder("Placeholder $it") } + adapter.items
delay(100)
recyclerView.smoothScrollToPosition(0)
delay(5000)
// Uncomment for workaround fix
// adapter.items = emptyList()
adapter.items = (0 until newArticlesCount).map { Item.Article("New article $it") } + adapter.items.drop(newArticlesCount)
}
}
Generally we can use the following code to go to the bottom if all data has been loaded into memory.
recyclerView.scrollToPosition(YourArraylist.size()-1);
But when using PagedListAdater and Room, the entity of the last item wasn't loaded at all. So when calling recyclerView.scrollToPosition, I can scroll with the scroll bar, but the data doesn't show. On my screen, I saw some words like "ABV.."; and if I scroll up/down manually, these view might be able to show correct.
BTW, I also tried ((LinearLayoutManager)recyclerView.getLayoutManager()).scrollToPositionWithOffset(index,0);, it doesn't work either.
The associated code is as below,
DataSource.Factory<Integer, ContactWithSectionView> dsFactory = contactDao.listAll();
concertList = new LivePagedListBuilder<>(dsFactory, 5)
.build();
concertList.observe((LifecycleOwner)context,(pagedList) -> {
this.adapter.submitList(pagedList);
});
#Dao
public interface ContactDao {
#Query("select * from ContactWithSectionView")
DataSource.Factory<Integer, ContactWithSectionView> listAll();
}
I tried to call concertList.getValue().loadAround(index) to load data before call recyclerView.scrollToPosition(int), it didn't work either. -- index is the position where I want to move to.
Finally, I gave up. didn't use the PagedListAdapter + Room, and load all items to memory in one time.
My outer RecyclerView crashes either with
IllegalArgumentException: Scrapped or attached views may not be recycled. isScrap:false isAttached:true...
or
IllegalStateException: The specified child already has a parent. You must call removeView() on the child's parent first.
Like the title suggests I have an RecyclerView in the list item layout of the first RecyclerView. This layout is used to display messages and the
inner RecyclerView to display attachments that come with the message. The inner RecyclerViews visibility is set to either GONE or VISIBLE depending whether the message has any attachments or not. The simplified outer list item layout looks like this
ConstraintLayout
TextView
TextView
TextView
RecyclerView
And the part of the adapter that handles the inner RecyclerView looks like this
private fun bindFiles(message: Message?) = with(itemView) {
if (message != null && message.attachments.isNotEmpty())
{
sent_message_attachments.setAsVisible()
sent_message_attachments.layoutManager = GridLayoutManager(this.context,Math.min(message.attachments.size,3))
sent_message_attachments.adapter = AttachmentAdapter(message.attachments)
sent_message_attachments.itemAnimator = null
sent_message_attachments.setHasFixedSize(true)
}
else{
sent_message_attachments.setAsGone()
sent_message_attachments.adapter = null
sent_message_attachments.layoutManager = null
}
}
The bug has something to do with the way I fetch the attachments in the inner adapter since once I disable the part that start the download process, everything is fine. There's no problem when loading images from the device, but once I start the download process, everything goes to hell. This is the part that handles images and kicks off the download process in the inner adapter. I have functions for videos and for other file types that are pretty much the same exact thing but use slightly different layout.
private fun bindImage(item: HFile?) = with(itemView) {
if (item != null)
{
if (item.isOnDevice && !item.path.isNullOrEmpty())
{
if (item.isGif)
{
attachment_image.displayGif(File(item.path))
}
else
{
attachment_image.displayImage(File(item.path))
}
}
else
{
//TODO: Add option to load images manually
FileHandler(item.id).downloadFileAsObservable(false)
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(
{ progress ->
//TODO: Show download process
},
{ error ->
error.printStackTrace()
//TODO: Enable manual retry
},
{ notifyItemChanged(adapterPosition)} //onComplete
)
}
}
}
I use the same structure as above in my DiscussionListAdapter to load discussion portraits (profile pictures etc.) and it does not have the same issue.
These are the extensions functions used to inflate the viewHolders and to display the images
fun ViewGroup.inflate(layoutRes: Int): View
{
return LayoutInflater.from(context).inflate(layoutRes, this, false)
}
fun ImageView.displayGif(file:File){
GlideApp.with(context).asGif().load(file).transforms(CenterCrop(), RoundedCorners(30)).into(this)
}
fun ImageView.displayImage(file:File){
GlideApp.with(context).load(file).transforms(CenterCrop(), RoundedCorners(30)).into(this)
}
I've been on this for the past couple of days and just can't get my head around it. Any help in any direction is greatly appreciated. I know my explanations can be a bit all over the place so just ask for clarification when needed :)
UPDATE
I have now been able to produce this with a GridLayout as well as with RecyclerView. It's safe to assume that the nested RecyclerViews were not the culprit here. I even tried to ditch the Rx-piece that handled loading the images and created an IntentService for the process, but the same crashes still occur.
With GridLayout I mean that instead of having another adapter to populate the nested RecyclerView I use only one adapter to populate the message and to inflate and populate views for the attachments as well and to attach those views to the nested GridLayout.
The crash happens when I start to download a file and then scroll the view, that is supposed to show the downloaded file, out of the screen. That view should get recycled but for some reason the download process (which in my test cases only takes around 100ms-400ms) causes the app to throw one of the two errors mentioned in the original question. It might be worth noting that I'm using Realm and the adapter takes in a RealmResults<Message> list as it's dataset. My presenter looks for changes in the list and then notifies the adapter when needed (changed due to the implementation of IntentService).
This is how I'm capable to reproduce this time and time again:
Open a discussion that has messages with attachments
Start to scroll upwards for more messages
Pass a message with an attachment and scroll it off screen while it's still loading
Crash
There is no crash if I stop and wait for the download to complete and everything works as intended. The image/video/file gets updated with a proper thumbnail and the app wont crash if I scroll that out of view.
UPDATE 2
I tried swapping the nested ViewGroup for a single ImageView just to see is the problem within the nestedness. Lo and behold! It still crashes. Now I'm really confused, since the DiscussionListAdapter I mentioned before has the same exact thing in it and that one works like a charm... My search continues. I hope someone, some day will benefit from my agony.
UPDATE 3
I started to log the parent of every ViewHolder in the onBindViewHolder() function. Like expected I got nulls after nulls after nulls, before the app crashed and spew this out.
04-26 21:54:50.718 27075-27075/com.hailer.hailer.dev D/MsgAdapter: Parent of ViewHolder: android.view.ViewOverlay$OverlayViewGroup{82a9fbc V.E...... .......D 0,0-1440,2168}
There's a method to my madness after all! But this just poses more questions. Why is ViewOverlay used here? As a part of RecyclerView or as a part of the dark magicians plans to deprive me of my sanity?
Sidenote
I went digging into RecyclerViews code to check if I could find a reason for the ViewOverlaymystery. I found out that RecyclerView calls the adapters onCreateViewHolder() function only twice. Both times providing itself as the parent argument for the function. So no luck there... What the hell can cause the item view to have the ViewOverlay as it's parent? The parent is an immutable value, so the only way for the ViewOverlay to be set as the parent, is for something to construct a new ViewHolder and supply the ViewOverlay as the parent object.
UPDATE 4
Sometimes I amaze myself with my own stupidity. The ViewOverlay is used because the items are being animated. I didn't even consider this to be an option since I've set the itemAnimator for the RecyclerView as null, but for some odd reason that does not work. The items are still being animated and that is causing this whole charade. So what could be the cause of this? (How I chose to ignore the moving items, I do not know, but the animations became very clear when I forced the app to download same picture over and over again and the whole list went haywire.)
My DiscussionInstanceFragment contains the RecyclerView in question and a nested ConstraintLayout that in turn contains an EditText for user input and a send button.
val v = inflater.inflate(R.layout.fragment_discussion_instance, container, false)
val lm = LinearLayoutManager(context)
lm.reverseLayout = true
v.disc_instance_messages_list.layoutManager = lm
v.disc_instance_messages_list.itemAnimator = null
v.disc_instance_messages_list.adapter = mPresenter.messageAdapter
This is the piece that handles the initialization of the RecyclerView. I'm most definitely setting the itemAnimator as null, but the animations just wont stop! I've tried setting the animateLayoutChanges xml attribute on the root ConstraintLayout and on the RecyclerView but neither of them worked. It's worth mentioning that I also checked whether the RecyclerView had an itemAnimator in different states of the program, and every time I check the animator, it is null. So what is animating my RecyclerView?!
I have faced the same issue
Try this in your child RecyclerView it works for me
RecyclerView childRC = itemView.findViewById(R.id.cmol_childRC);
layoutManager = new LinearLayoutManager(context);
childRC.setItemAnimator(null);
childRC.setLayoutManager(layoutManager);
childRC.setNestedScrollingEnabled(false);
childRC.setHasFixedSize(true);
now set your Adapter like this
ArrayList<Model> childArryList = new ArrayList<>();
childArryList.addAll(arrayList.get(position).getArrayList());
ChildOrderAdapter adapter = new ChildOrderAdapter(context, childArryList);
holder.childRC.swapAdapter(adapter, true);
hope this helps
I finally figured out what was causing this. In my DiscussionInstanceView I have a small view that is animated into and out of view with ConstraintLayout keyframe animations. This view only shows the download progress of the chat history and is used only once, when the discussion is first opened. BUT since I had a call to hiding that view every time my dataset got updated, I was forcing the ConstraintLayout to fire of an animation sequence thus making everything animate during the dataset update. I just added a simple check whether I was downloading the history or not and this problem got fixed.