Develop Reference

ViewPager (RecyclerView) with custom item count doesn't update data properly

I've created an adapter (extending ListAdapter with DiffUtil.ItemCallback) for my RecyclerView. It's an ordinary adapter with several itemViewTypes, but it should be smth like cyclic, if API sends flag and dataset size is > 1 (made by overriding getItemCount() to return 1000 when conditions == true).
When I change app locale through app settings, my fragment recreates, data loads asynchronously (reactively, several times in a row, from different requests, depending on several rx fields, which causes data set to be a combination of data on different languages just after locale is changed (in the end all dataset is correctly translated btw) (make it more like synchronous is not possible because of feature specifics)), posting its values to LiveData, which triggers updates of recycler view, the problem appears:
After last data set update some of the views (nearest to currently displayed and currently displayed) appear not to be translated.
Final data set, which is posted to LiveData is translated correctly, it even has correct locale tag in its id. Also after views are recycled and we return back to them - they are also correct.
DiffUtil is computed correctly also (I've tried to return only false in item callbacks and recycler view still didn't update its view holders correctly).
When itemCount == list.size everything works fine.
When adapter is pretending to be cyclic and itemCount == 1000 - no.
Can somebody explain this behaviour and help to figure out how to solve this?
Adapter Code Sample:
private const val TYPE_0 = 0
private const val TYPE_1 = 1
class CyclicAdapter(
val onClickedCallback: (id: String) -> Unit,
val onCloseClickedCallback: (id: String) -> Unit,
) : ListAdapter<IViewData, RecyclerView.ViewHolder>(DataDiffCallback()) {
var isCyclic: Boolean = false
set(value) {
if (field != value) {
field = value
}
}
override fun getItemCount(): Int {
return if (isCyclic) {
AdapterUtils.MAX_ITEMS // 1000
} else {
currentList.size
}
}
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder {
return when (viewType) {
TYPE_0 -> Type0.from(parent)
TYPE_1 -> Type1.from(parent)
else -> throw ClassCastException("View Holder for ${viewType} is not specified")
}
}
override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
when (holder) {
is Type0 -> {
val item = getItem(
AdapterUtils.actualPosition(
position,
currentList.size
)
) as ViewData.Type0
holder.setData(item, onClickedCallback)
}
is Type1 -> {
val item = getItem(
AdapterUtils.actualPosition(
position,
currentList.size
)
) as ViewData.Type1
holder.setData(item, onClickedCallback, onCloseClickedCallback)
}
}
}
override fun getItemViewType(position: Int): Int {
return when (val item = getItem(AdapterUtils.actualPosition(position, currentList.size))) {
is ViewData.Type0 -> TYPE_0
is ViewData.Type1 -> TYPE_1
else -> throw ClassCastException("View Type for ${item.javaClass} is not specified")
}
}
class Type0 private constructor(itemView: View) :
RecyclerView.ViewHolder(itemView) {
fun setData(
viewData: ViewData.Type0,
onClickedCallback: (id: String) -> Unit
) {
(itemView as Type0View).apply {
acceptData(viewData)
setOnClickedCallback { url ->
onClickedCallback(viewData.id,)
}
}
}
companion object {
fun from(parent: ViewGroup): Type0 {
val view = Type0View(parent.context).apply {
layoutParams =
LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT)
}
return Type0(view)
}
}
}
class Type1 private constructor(itemView: View) :
RecyclerView.ViewHolder(itemView) {
fun setData(
viewData: ViewData.Type1,
onClickedCallback: (id: String) -> Unit,
onCloseClickedCallback: (id: String) -> Unit
) {
(itemView as Type1View).apply {
acceptData(viewData)
setOnClickedCallback { url ->
onClickedCallback(viewData.id)
}
setOnCloseClickedCallback(onCloseClickedCallback)
}
}
companion object {
fun from(parent: ViewGroup): Type1 {
val view = Type1View(parent.context).apply {
layoutParams =
LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT)
}
return Type1(view)
}
}
}
}
ViewPager Code Sample:
class CyclicViewPager #JvmOverloads constructor(
context: Context,
attrs: AttributeSet? = null,
defStyleAttr: Int = 0
) : FrameLayout(context, attrs, defStyleAttr),
ICyclicViewPager {
private val cyclicViewPager: ViewPager2
private lateinit var onClickedCallback: (id: String) -> Unit
private lateinit var onCloseClickedCallback: (id: String) -> Unit
private lateinit var adapter: CyclicAdapter
init {
LayoutInflater
.from(context)
.inflate(R.layout.v_cyclic_view_pager, this, true)
cyclicViewPager = findViewById(R.id.cyclic_view_pager)
(cyclicViewPager.getChildAt(0) as RecyclerView).apply {
addItemDecoration(SpacingDecorator().apply {
dpBetweenItems = 12
})
clipToPadding = false
clipChildren = false
overScrollMode = RecyclerView.OVER_SCROLL_NEVER
}
cyclicViewPager.offscreenPageLimit = 3
}
override fun initialize(
onClickedCallback: (id: String) -> Unit,
onCloseClickedCallback: (id: String) -> Unit
) {
this.onClickedCallback = onClickedCallback
this.onCloseClickedCallback = onCloseClickedCallback
adapter = CyclicAdapter(
onClickedCallback,
onCloseClickedCallback,
).apply {
stateRestorationPolicy = RecyclerView.Adapter.StateRestorationPolicy.PREVENT_WHEN_EMPTY
}
cyclicViewPager.adapter = adapter
}
override fun setState(viewPagerState: CyclicViewPagerState) {
when (viewPagerState.cyclicityState) {
is CyclicViewPagerState.CyclicityState.Enabled -> {
adapter.submitList(viewPagerState.pages) {
adapter.isCyclic = true
cyclicViewPager.post {
cyclicViewPager.setCurrentItem(
// Setting view pager item to +- 500
AdapterUtils.getCyclicInitialPosition(
adapter.currentList.size
), false
)
}
}
}
is CyclicViewPagerState.CyclicityState.Disabled -> {
if (viewPagerState.pages.size == 1 && adapter.isCyclic) {
cyclicViewPager.setCurrentItem(0, false)
adapter.isCyclic = false
}
adapter.submitList(viewPagerState.pages)
}
}
}
}
Adapter Utils Code:
object AdapterUtils {
const val MAX_ITEMS = 1000
fun actualPosition(position: Int, listSize: Int): Int {
return if (listSize == 0) {
0
} else {
(position + listSize) % listSize
}
}
fun getCyclicInitialPosition(listSize: Int): Int {
return if (listSize > 0) {
MAX_ITEMS / 2 - ((MAX_ITEMS / 2) % listSize)
} else {
0
}
}
}
Have tried not to use default itemView variable of RecyclerView (became even worse).
Tried to make diff utils always return false, to check if it calculates diff correctly (yes, correctly)
Tried to add locale tags to ids of data set items (didn't help to solve)
Tried to post empty dataset on locale change before setting new data to it (shame on me, shouldn't even think about it)
Tried do add debounce to rx to make it wait a bit before update (didn't help)
UPD: When I call adapter.notifyDatasetChanged() manually, which is not the preferred way, everything works fine, so the question is why ListAdapter doesn't dispatch notify callbacks properly in my case?

The issue with ListAdapter is that it doesn't clearly state that you need to supply a new list for it to function.
In other words, the documentation says: (and I quote the source code):
/**
* Submits a new list to be diffed, and displayed.
* <p>
* If a list is already being displayed, a diff will be computed on a background thread, which
* will dispatch Adapter.notifyItem events on the main thread.
*
* #param list The new list to be displayed.
*/
public void submitList(#Nullable List<T> list) {
mDiffer.submitList(list);
}
The key word being new list.
However, as you can see there, all the adapter does is defer to the DiffUtil and calls submitList there.
So when you look at the actual source code of the AsyncListDiffer you will notice it does, at the beginning of its code block:
if (newList == mList) {
// nothing to do (Note - still had to inc generation, since may have ongoing work)
if (commitCallback != null) {
commitCallback.run();
}
return;
}
In other words, if the new list (reference) is the same as the old one, regardless of their contents, don't do anything.
This may sound cool but it means that if you have this code, the adapter will not really update:
(pseudo...)
var list1 = mutableListOf(...)
adapter.submitList(list1)
list1.add(...)
adapter.submitList(list1)
The reason is list1 is the same reference your adapter has, so the differ exits prematurely, and doesn't dispatch any changes to the adapter.
Quite obscure, I know.
The solution, as pointed in many SO answers is to create a copy of the list itself.
Most users do
var list1 = mutableListOf(...)
adapter.submitList(list1)
var list2 = list1.toMutableList()
list2.add(...)
adapter.submitList(list2)
The call to toMutableList() creates a new list containing the items of list1 and so the comparison above if (newList == mList) { should now be false and the normal code should execute.
UPDATE
Keep in mind that a lot of developers make the mistake of...
var list = mutableListOf...
adapter.submitList(list)
list.add(xxx)
adapter.submitList(list.toList())
This doesn't work, because the new list you create, is referencing the same objects the adapter has. This means that both lists list and list.toList() are pointing to the same things despite being two instances of an ArrayList.
But the side-effect is that DiffUtil compares the items and they are the same, so no diff is dispatched to the adapter either.
The correct sequence is...
val list = mutableListOf(...)
adapter.submitList(list.toList())
// Make a copy first, so we can alter it as we please without the *current list held by the adapter* from being affected.
var modified = list.toMutableList()
modified.add(...)
adapter.submitList(modified)

After taking a look at your sample in GitHub, I was able to reproduce the issue. With only about 30-40 minutes of playing with it, I can say that I'm not 100% sure what component is not updating.
Things I've noticed.
The onBindViewHolder method is not called when you change the locale (except maybe the 1st time?).
I do not understand why the need to post to the adapter after you've submitted the list in the callback:
cyclicViewPager.setCurrentItem(
// Setting view pager item to +- 500
AdapterUtils.getCyclicInitialPosition(
adapter.currentList.size
), false
)
Why ? This means the user loses their current position.
Why not keep the existing?
I noticed you do cyclicViewPager.offscreenPageLimit = 3 this effectively disables the RecyclerView "logic" for handling changes, and uses instead the usual ViewPager state adapter logic of "prefetching/keeping" N (3 in your case) pages in "advance".
At first I thought this was causing issues, but removing it (which sets it to -1 which is the default and the "use RecyclerView" value, didn't make a big change (though I did notice some changes here and there, as in it would sometimes update the current one -but not the next ones within 2~3 pages).
The documentation says:
Set the number of pages that should be retained to either side of the currently visible page(s). Pages beyond this limit will be recreated from the adapter when needed. Set this to OFFSCREEN_PAGE_LIMIT_DEFAULT to use RecyclerView's caching strategy.
So I would have imagined that the default value would be aided by the ListAdapter and its DiffUtil. Doesn't seem to be the case.
What I did try (among a few other things) was to see if the issue was in the actual adapter (or at least the viewPager dependency on its adapter). I ran out of time (work!) but I noticed that if you do:
override fun setState(viewPagerState: CyclicViewPagerState) {
when (viewPagerState.cyclicityState) {
is CyclicViewPagerState.CyclicityState.Enabled -> {
// call initialize again, to recreate the adapter
initialize(this.onClickedCallback, this.onCloseClickedCallback)
adapter.submitList(viewPagerState.pages) {
adapter.isCyclic = true
// Setting vp item to ... (code omitted for brevity)
}
This works. It's theoretically less efficient as you're recreating the whole adapter, but in your example you're effectively creating an ENTIRE new set of data changing every ID, so in terms of performance, I'd argue this is more efficient as there's no need to recalculate changes and dispatch them, since to the eyes of the Diff Util, all the rows are different. By recreating the adapter, well... the VP has to reinit anyway.
I noticed this worked fine in your example.
I went ahead and added two more things, because the "silly" adapter cannot reliably tell you which position is the current... you can naively save it:
In CyclicViewPager:
var currentPos: Int = 0
init {
...
this.cyclicViewPager.registerOnPageChangeCallback(object : OnPageChangeCallback() {
override fun onPageSelected(position: Int)
currentPos = position
}
})
}
And then
is CyclicViewPagerState.CyclicityState.Enabled -> {
initialize(this.onClickedCallback, this.onCloseClickedCallback)
adapter.submitList(viewPagerState.pages) {
adapter.isCyclic = true
if (adapter.currentList.size <= currentPos) {
cyclicViewPager.setCurrentItem(currentPos, false)
} else {
cyclicViewPager.setCurrentItem(
// Setting view pager item to +- 500
AdapterUtils.getCyclicInitialPosition(
adapter.currentList.size
), false
)
}
}
}
This does work, but of course, you're recreating the entire VP adapter again, so it may not be desired.
At this point, I'd either need to spend much more time trying to figure out which part of VP, RV, or its dependencies is not "dispatching" the correct data. My guess would be somewhere around some silly ViewPager optimization combined with Android terribly unreliable View system, not picking a message in the queue; but I may be also terribly wrong ;)
I hope someone smarter and/or with more coffee in their system can find out a simpler solution.
(all in all, I found the sample project relatively easy to navigate, but the design of your data a bit convoluted, but... as it was a sample, it's hard to tell what "real-life" data structures you really have).

Jetpack Compose: LazyRow onScrollListener

I was wondering if there is a way or a resource I could refer to in order to achieve a side effect on a LazyRow when an item is scrolled?
The side effect is basically to call a function in the viewModel to alter the state of the list's state.
The side effect should be only executed only if the current firstVisibleItemIndex after
scroll is different than before
The side effect should not be executed the item is not fully scrolled
I am implementing a fullscreen LazyRow items with a snap behavior
So far I have tried NestedScrollConnection
class OnMoodItemScrolled : NestedScrollConnection {
override suspend fun onPostFling(consumed: Velocity, available: Velocity): Velocity {
viewModel.fetchItems()
return super.onPostFling(consumed, available)
}
}
The issue with the above is that the side effect is going to be executed anyway even-though the item displayed after the scroll is the same as before the scroll.
I also tried to collecting the listState interaction as the following
val firstVisibleItem: Int = remember { sectionItemListState.firstVisibleItemIndex }
sectionItemListState.interactionSource.collectIsDraggedAsState().let {
if (firstVisibleItem != sectionItemListState.firstVisibleItemIndex) {
viewModel.fetchItems()
}
}
The issue with the above is that the side effect is going to be executed the second the composable is composed for the first time.

You can use the LazyListState#firstVisibleItemIndex to get the information about the first visible item and store this value. When the value changes the item is scrolled up.
Something like:
#Composable
private fun LazyListState.itemIndexScrolledUp(): Int {
var previousIndex by remember(this) { mutableStateOf(firstVisibleItemIndex) }
return remember(this) {
derivedStateOf {
if (firstVisibleItemIndex > previousIndex) {
//scrolling up
previousIndex
} else {
- 1
}.also {
//Update the previous index
previousIndex = firstVisibleItemIndex
}
}
}.value
}
and then:
val state = rememberLazyListState()
var index = state.itemIndexScrolledUp()
DisposableEffect(index){
if (index != -1) {
//...item is scrolled up
}
onDispose { }
}
LazyColumn(
state = state,
){
//...
}

I solved my issue using a LaunchedEffect with 2 keys.
val sectionItemListState = rememberLazyListState()
val flingBehavior = rememberSnapFlingBehavior(sectionItemListState)
var previousVisibleItemIndex by rememberSaveable {
mutableStateOf(0)
}
val currentVisibleItemIndex: Int by remember {
derivedStateOf { sectionItemListState.firstVisibleItemIndex }
}
val currentVisibleItemScrollOffset: Int by remember {
derivedStateOf { sectionItemListState.firstVisibleItemScrollOffset }
}
LaunchedEffect(currentVisibleItemIndex, currentVisibleItemScrollOffset) {
if (previousVisibleItemIndex != currentVisibleItemIndex && currentVisibleItemScrollOffset == 0) {
// The currentVisible item is different than the previous one && it's fully visible
viewModel.fetchItems()
previousVisibleItemIndex = currentVisibleItemIndex
}
}
Using both currentVisibleItemIndex and currentVisibleItemScrollOffset as keys will make sure that the LaunchedEffect will be triggered whenever one of them changes. Moreover, checking if the previousVisibleItemIndex is different than the currentVisibleItemIndex will ensure that we only trigger this effect only if the visible item is changing.
However, this condition will true also if the use has partially scrolled and since I have a snapping effect it will go back to the previous position. Which will result in triggering the effect twice.
In order to make sure that we only trigger the effect only in case were we actually scrolled to the next/previous fully visible position we need to rely on the scrollOffset.

is there any alternate for arraylist.remove(element) function?

my recycler view reloads with spinner value, selected data is stored in a global arraylist, and here is my recycler view code to do the selection and deselection. Selection and deselection works just fine, but when i select and change spinner value, and then come to back original spinner value, where items are already selected, deselction happens, but item is not removed from the global arraylist. While debugging i found that cursor reaches there, but i dont know why .remove() isnt working. Is there any alternative for it or am i doing wrong? Is there anything i should know that why isnt the item removed.
.
.
.
class RecyclerViewAdapter(val dataList:ArrayList<ModelClass>,val onItemClicked: (Int) -> Unit):RecyclerView.Adapter<RecyclerViewAdapter.ViewHolder>() {
object ob {
val dataSelected = ArrayList<ModelClass>()
val hm = HashMap<ModelClass,String>()
}
fun setData(listModel: List<ModelClass>) {
dataList.clear()
dataList.addAll(listModel)
notifyDataSetChanged()
}
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
val binding = ItemViewBinding.inflate(
LayoutInflater.from(parent.context), parent, false
)
return ViewHolder(binding, parent.context)
}
#SuppressLint("ResourceAsColor")
override fun onBindViewHolder(holder: ViewHolder, position: Int) {
holder.bindItems(dataList[position])
}
override fun getItemCount() = dataList.size
inner class ViewHolder(
val binding: ItemViewBinding,
val context: Context
) : RecyclerView.ViewHolder(binding.root) {
var count=0
#SuppressLint("ResourceAsColor")
fun restore() {
for (i in 0 until ob.dataSelected.size) {
for (j in 0 until dataList.size) {
if (ob.dataSelected[i].sku_code == (dataList[j]).sku_code) {
if (adapterPosition == j) {
itemView.isSelected = true
itemView.setBackgroundColor(R.color.black)
count=count+1
println("****")
}
}
}
}
if(!itemView.isSelected){
itemView.isSelected = false
itemView.setBackgroundResource(0)
}
}
#SuppressLint("ResourceAsColor", "ResourceType")
fun bindItems(data: ModelClass) = with(binding) {
binding.itemQuant.text = data.item_quant
binding.itemName.text = data.item_name
binding.mfgName.text = data.mfg
binding.quantity.text = data.item_stock.toString()
count=0
restore()
itemView.setOnClickListener {
count += 1
var isPresent:Int
if (count%2 == 0){
isPresent=1
}
else
{
isPresent=0
}
if (isPresent == 1) {
it.setBackgroundResource(0) //works
ob.dataSelected.remove(dataList[adapterPosition]) //doesnt work if spinner value is changed and changed back. works while still on same screen.
} else {
if (isPresent == 0) {
it.setBackgroundColor(R.color.black)
ob.dataSelected.add(dataList[adapterPosition])
}
// onItemClicked.invoke(adapterPosition)
}
}
}
}
}

Are you sure it's not being removed? Have you set a breakpoint and checked the contents of the array (or just logged it)? Because it looks like when you're binding a viewholder, you just check if the item is in dataSelected, and if it is you set the view's selected and backgroundColor values. It doesn't look like you change them back if it's not in dataSelected, so that selected appearance "sticks".
It looks like you're trying to reset them with this:
if(!itemView.isSelected){
itemView.isSelected = false
itemView.setBackgroundResource(0)
}
but that only works if itemView.selected hasn't been set to true, which it has if your item is in dataSelected. You need to do it like this:
for (i in 0 until ob.dataSelected.size) {
for (j in 0 until dataList.size) {
// rolling multiple conditions into a single value makes it easier to do an if/else
val selected = ob.dataSelected[i].sku_code == (dataList[j]).sku_code && adapterPosition == j
if (selected) {
itemView.isSelected = true
itemView.setBackgroundColor(R.color.black)
count=count+1
println("****")
} else {
itemView.isSelected = false
itemView.setBackgroundResource(0)
}
}
}
That way you're always updating the contents of the view holder to reflect the state of the current item. That's especially important in RecyclerViews, because the point of those is that the ViewHolders get reused to display different items, and any View attributes you don't set when binding (e.g. colours, checkbox statuses) will just stay on whatever they were last set to when displaying some other item.
btw, you can simplify that looping situation by just checking if anything in dataSelected has the SKU you're looking for:
val itemSku = datalist[adapterPosition].sku_code
val selected = ob.dataSelected.any { it.sku_code == itemSku }
ideally you wouldn't be using adapterPosition to find the current item either - the item you're matching is passed in to bindItems (as data), you could just pass that to your restore function
edit if the items aren't being removed from dataSelected, at a guess it's because the object you're fetching from dataList "doesn't exist" in dataSelected. By "doesn't exist" I mean there isn't an object that equals the one you're trying to remove.
ob.dataSelected.remove(dataList[adapterPosition])
I'm assuming that might be the case because you're not doing straight object comparisons when you're checking if an item is in the selected array, you're specifically comparing their sku_code values instead
if (ob.dataSelected[i].sku_code == (dataList[j]).sku_code)
If you can't just do if (obj.dataSelected[i] == dataList[j]), then remove won't work either - it's the same check. So maybe you need to look into making those objects equal (e.g. using data classes if that works for what you're doing), or use removeAll with a predicate (remove only works with a specific item):
ob.dataSelected.removeAll { it.sku_code == dataList[adapterPosition].sku_code }
You'll still have the problem of the UI not being updated though, like the first part of the answer explains! So you might have two problems here

change this line
ob.dataSelected.add(dataList[adapterPosition])
to this
ob.dataSelected.add(dataList[adapterPosition].copy)
Don't forget to call notfiyDatasetChanged() after that

MotionLayout Expanding Recycler List View - how to reset a transition

I feel like I am being silly,
I want to use MotionLayout on an ViewHolder within my RecyclerView to animate between two states (the current playing song is expanded, while the last playing song is shrunk)
However it seems that the recyclerview is too good, it simply changes the contents without changing the views, i.e. when the current playing song changes, the view is already in the End Transition state, so my transition does nothing.
Same my previously expanded item is rebound into the closed state so my animation does nothing.
So Okay i thought lets check the state of the transition and set the progress, but this leads to the transition not running if i set the progress the line before. I have tried, adding in some delays but no real improvement,
I feel like maybe I am over engineering this, or I am missing something fundamental about how to reset motionlayout animations.. Any help will be much appreciated.
override fun onBindViewHolder(holder: SongViewHolder, position: Int) {
if (songs.isNotEmpty() && position < songs.size) {
val current = songs[position]
holder.songName?.text = current.song
holder.albumArt?.setImageResource(current.albumArtId)
holder.artistName?.text = current.artist
var ml = holder.motionLayout
if (current.currentPlaying){
//The view is recycled so its already in the end state... so set it to the start state and animate
if (ml?.progress!! > 0f) {
ml?.progress = 0f //<- This resets the animation state
}
ml?.transitionToEnd() <- but at this point the animation does not work if i have manually set the progress the line above
}else{
if (current.previoussong){
//The view that was last expended is not in the end state, so set it then transation to start
if (ml?.progress!! < 1f) {
ml?.progress = 1f
}
ml?.transitionToStart()
}
}
}
}

Okay incase anyone has the same issue, i found "an" answer to my dilemma.
Insteead of setting the progress, i explicitly set the transition then asked it to transition to end, this worked for expand.
And to get shrink working i had to create a different initial layout with an inverted motionscene, then transition to the end, and set the "previoussong" as a different viewType in my creatViewHolder
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): SongViewHolder {
//Use the int to switch?
val itemView : View = when (viewType) {
TYPEPLAYING -> inflater.inflate(R.layout.list_motion_layout, parent, false)
TYPEUPCOMING -> inflater.inflate(R.layout.list_motion_layout, parent, false)
TYPEPREVIOUS -> inflater.inflate(R.layout.list_motion_layout_shrink, parent, false)
else
-> inflater.inflate(R.layout.footer, parent, false)
}
...
}
override fun onBindViewHolder(holder: SongViewHolder, position: Int) {
if (songs.isNotEmpty() && position < songs.size) {
val current = songs[position]
holder.songName?.text = current.song
holder.albumArt?.setImageResource(current.albumArtId)
holder.artistName?.text = current.artist
var ml = holder.motionLayout
if (current.currentPlaying){
ml?.setTransition(list_motion_layout_start, currentplaying_song)
ml?.transitionToEnd()
}
if (current.previouslyPlaying) {
ml?.setTransition(currentplaying_song, list_motion_layout_start) // Not sure if this is actually required
ml?.transitionToEnd()
}
}
}
All in all i have a working expand/shrink list adapter using motionview it looks quite nice, but there is probably nicer ways to do this out there ,,, sorry cant share any pics.

Android/Kotlin - LAGGY Checking item in BottomNavigationView from ViewPager

I am fairly new to programming, and this is my first large/real project.
--Background--
I have a ViewPager set up within my MainActivity, that slides between 3 different fragments. In Addition, one fragment requires menu items within the toolbar, and a BottomNavigationView is held within the MainActivity.
Each time i move to a new item/page of the ViewPager, i want to select(check) the corresponding page item within the BottomNavView.
I have attempted multiple configurations of the one below, but can't get it perfect
--The Problem--
The time it takes to perform bottom_navigation.menu.getItem(pos).isChecked = true is too long... Approx 50ms on my HTC One, or 100ms in the emulator.
This delay causes the ViewPager scrolling action to be jarred/laggy.
I would like to know if there is a different way to check or highlight the corresponding item within the BottomNavBar, or more desirably, perform the checking action at the same time without impeding the scrolling animation of the ViewPager.
--Attempted Fixes--
Perform check within onPageSelected - (Result is slightly more laggy)
Perform check when scroll state is IDLE - (Results in smooth pager scroll, but the checked item is 'left behind' and updated too late, particularly when scrolling fast)
Find the navigation item in Anko's doAsync{ } - (Results don't change)
// Adds a page-change listener
viewPager.addOnPageChangeListener(object : ViewPager.OnPageChangeListener {
// Set Toolbar title and menu items
override fun onPageSelected(position: Int) {
when (position) {
0 -> {
supportActionBar!!.title = "Page1"
toolbar.menu.setGroupVisible(0, false)
}
1 -> {
supportActionBar!!.title = "Page2"
if (toolbar.menu.size() == 0) {
toolbar.inflateMenu(R.menu.toolbar_list_menu)
} else {
toolbar.menu.setGroupVisible(0, true)
}
}
2 -> {
supportActionBar!!.title = "Page3"
toolbar.menu.setGroupVisible(0, false)
}
}
}
// While view pager settling on new item/page, check the correct bottom navigation view item
override fun onPageScrollStateChanged(state: Int) {
if (state == ViewPager.SCROLL_STATE_SETTLING) {
val pos = viewPager.currentItem
bottom_navigation.menu.getItem(pos).isChecked = true
}
}
// Not needed, must be implemented
override fun onPageScrolled(position: Int, positionOffset: Float, positionOffsetPixels: Int) {}
})
I really hope someone has an answer to help with my apps performance :)
Thanks for your time.