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st...@viber.com
Project: platform/frameworks/support
Branch: androidx-main
commit 16278c75a09262bfc2b1e230730f79ec5a4d4918
Author: Andrey Kulikov <andreykulikov@google.com>
Date: Tue May 25 18:25:16 2021
Do not reset initial scroll position in LazyColumn/Row when items are loaded asynchronously
If the initial scroll position(or restored scroll position) is not 0 this value will be immediately overridden by 0 if there were no items yet provided for LazyColumn/Row.
It is easily reproducible with Paging where we start loading asynchronously and there is always a first frame when we don't have any items.
Fixes: 177245496
Test: new tests for LazyColumn and LazyRow
Change-Id: I95e374fb06dc480aab7b56b8b3cacb92ca1188a9
M compose/foundation/foundation/src/androidAndroidTest/kotlin/androidx/compose/foundation/lazy/LazyColumnTest.kt
M compose/foundation/foundation/src/androidAndroidTest/kotlin/androidx/compose/foundation/lazy/LazyRowTest.kt
M compose/foundation/foundation/src/commonMain/kotlin/androidx/compose/foundation/lazy/LazyListState.kt
https://android-review.googlesource.com/1717757
Branch: androidx-main
commit 16278c75a09262bfc2b1e230730f79ec5a4d4918
Author: Andrey Kulikov <andreykulikov@google.com>
Date: Tue May 25 18:25:16 2021
Do not reset initial scroll position in LazyColumn/Row when items are loaded asynchronously
If the initial scroll position(or restored scroll position) is not 0 this value will be immediately overridden by 0 if there were no items yet provided for LazyColumn/Row.
It is easily reproducible with Paging where we start loading asynchronously and there is always a first frame when we don't have any items.
Fixes: 177245496
Test: new tests for LazyColumn and LazyRow
Change-Id: I95e374fb06dc480aab7b56b8b3cacb92ca1188a9
M compose/foundation/foundation/src/androidAndroidTest/kotlin/androidx/compose/foundation/lazy/LazyColumnTest.kt
M compose/foundation/foundation/src/androidAndroidTest/kotlin/androidx/compose/foundation/lazy/LazyRowTest.kt
M compose/foundation/foundation/src/commonMain/kotlin/androidx/compose/foundation/lazy/LazyListState.kt
cl...@google.com
I think this issue still exists. The fix could break easily when you add a header item to LazyColumn.
ap...@google.com
Yes, we basically just changed the default behavior for the empty case for now. Please track this bug
cl...@google.com
Also, the itemCount always started from 0 when navigated back. I can't identify whether it is really empty or just a temporary state. Especially if I need to show an empty UI, it will flash shortly then display the paging data.
My workaround currently is to keep `LazyPagingItems` object in `ViewModel`, so that `itemCount` and other state will be the same when navigated back.
My workaround currently is to keep `LazyPagingItems` object in `ViewModel`, so that `itemCount` and other state will be the same when navigated back.
pr...@google.com
yes, it is expected as the paging is starting loading asynchronously and there is always at least one frame when there is no items yet
va...@gmail.com
But we need a mechanism to display an empty UI when there is really no data. Blink screen is definitely not good for UX.
cl...@google.com
As it is not really related to the initial issue described in this bug don't you mind filing a separate bug here
https://issuetracker.google.com/issues/new?component=413106&template=1096385
so we can discuss this separately.
Thanks!
so we can discuss this separately.
Thanks!
ma...@kayak.com
Where can I find the new bug? this issue affect me as well.
cl...@google.com
>My workaround currently is to keep `LazyPagingItems` object in `ViewModel`, so that `itemCount` and other state will be the same when navigated back.
Can you provide an example? In my case stored `LazyPagingItems` object does not want to load data
upd: No longer needed. In my case the issue with LazyVerticalGrid. For myself I found solution - I made copy of LazyPagingItems to make counstructor public and create LazyPagingItems inside ViewModel, so reloading does not occur when navigating backwards
Can you provide an example? In my case stored `LazyPagingItems` object does not want to load data
upd: No longer needed. In my case the issue with LazyVerticalGrid. For myself I found solution - I made copy of LazyPagingItems to make counstructor public and create LazyPagingItems inside ViewModel, so reloading does not occur when navigating backwards
ja...@go-text.me
deleted
cl...@google.com
LazyPagingItems is not intended to be the persistent data storage, it is just a simple wrapper to be used in the ui layer. The Pager data should be cached in the ViewModel instead.
You probably want to try to use `.cachedIn(viewModelScope)`. Seehttps://developer.android.com/topic/libraries/architecture/paging/v3-paged-data#pagingdata-stream .
You probably want to try to use `.cachedIn(viewModelScope)`. See
ja...@go-text.me
Thanks for reply. As I am not good English, I think that the words were misrepresented.
I mean that `.cachedIn(viewModelScope)` in the ViewModel solved my scroll state issue.
I mean that `.cachedIn(viewModelScope)` in the ViewModel solved my scroll state issue.
va...@gmail.com
In my case .cachedIn(viewModelScope) preserves data from loading again, but scroll position is still resetting to the start every time I navigate to another composable and back. I use LazyColumn with header (item element before items), so that might be the case
cl...@google.com
Check if you have any other item in the LazyList outside the paged items it will lose position.
If you have any comment it out and see if it still lose position.
va...@gmail.com
We are facing the same issue even after applied cachedIn(viewModelScope), in our scenario we are using compose navigation, and when navigating to other compose screens and return back will void the LazyColumn scroll state.
We are using paging 3 for loading with LazyPagingItems.
var listState: LazyListState //declared in the viewmodel
sample:
LazyColumn(
state = listState,
modifier = Modifier
.fillMaxWidth()
) {
items(items = lazyListingItems,)
{
ListingCard(), onClick = {
navHostController.navigate(Routes.detail)
}
)
}
}
Please help to solve this.
We are using paging 3 for loading with LazyPagingItems.
var listState: LazyListState //declared in the viewmodel
sample:
LazyColumn(
state = listState,
modifier = Modifier
.fillMaxWidth()
) {
items(items = lazyListingItems,)
{
ListingCard(), onClick = {
navHostController.navigate(Routes.detail)
}
)
}
}
Please help to solve this.
pk...@tango.me
I think that should work if you create a state inside composition via rememberLazyListState(). What is your motivation to move it into a ViewModel?
I think what happens is when you go to other screen your state still exist together with the ViewModel, then when you go back to the original screen lazyListingItems are recreated, and as Paging provides the values via a Flow there is no way to get the data synchronously, so there is always at least the first frame where lazyListingItems has 0 items yet, then LazyColumn is populated with 0 items so it has to reset the scroll position. It can't differentiate between the events where there are no items anymore and there are no items yet.
But if the LazyListState will be recreated as part of the recomposition then it can postpone the scroll position restoration till the first frame when there are at least 1 element in the list
I think what happens is when you go to other screen your state still exist together with the ViewModel, then when you go back to the original screen lazyListingItems are recreated, and as Paging provides the values via a Flow there is no way to get the data synchronously, so there is always at least the first frame where lazyListingItems has 0 items yet, then LazyColumn is populated with 0 items so it has to reset the scroll position. It can't differentiate between the events where there are no items anymore and there are no items yet.
But if the LazyListState will be recreated as part of the recomposition then it can postpone the scroll position restoration till the first frame when there are at least 1 element in the list
Description
Despite the fact that bug
Steps to reproduce:
java.lang.IndexOutOfBoundsException: Inconsistency detected. Invalid item position 156(offset:156).state:1000 androidx.recyclerview.widget.RecyclerView{e95134d VFED..... ........ 0,367-1080,2205 #7f08016c app:id/recycler}, adapter:com.example.badsearch.MainRecyclerAdapter@be8de02, layout:androidx.recyclerview.widget.LinearLayoutManager@d575313, context:com.example.badsearch.MainActivity@3b66302 at androidx.recyclerview.widget.RecyclerView$Recycler.tryGetViewHolderForPositionByDeadline(RecyclerView.java:6364) at androidx.recyclerview.widget.GapWorker.prefetchPositionWithDeadline(GapWorker.java:288) at androidx.recyclerview.widget.GapWorker.flushTaskWithDeadline(GapWorker.java:345) at androidx.recyclerview.widget.GapWorker.flushTasksWithDeadline(GapWorker.java:361) at androidx.recyclerview.widget.GapWorker.prefetch(GapWorker.java:368) at androidx.recyclerview.widget.GapWorker.run(GapWorker.java:399) at android.os.Handler.handleCallback(Handler.java:958) at android.os.Handler.dispatchMessage(Handler.java:99) at android.os.Looper.loopOnce(Looper.java:230) at android.os.Looper.loop(Looper.java:319) at android.app.ActivityThread.main(ActivityThread.java:9063) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:588) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1103)