today I was trying to implement custom ads inside a horizontally oriented recycler view.
Everything went fine, till I ran the app and noticed that some of the items inside my MutableList are not displayed (or are being displayed as blank spaces, don't know for sure) and right after every ad (only does that after ads) there's a huge blank space.
I don't know what to do to solve this, I'm not familiar with multiple layouts inside an adapter.
Adapter declaration:
class CardAdapter (val context2: Context, private val Cards:MutableList<Card>) : RecyclerView.Adapter<RecyclerView.ViewHolder>()
This is my ad holder inside the adapter:
inner class HolderNativeAd(itemView: View): RecyclerView.ViewHolder(itemView){
val app_ad_background : ImageView = itemView.findViewById(R.id.ad_icon)
val ad_headline : TextView = itemView.findViewById(R.id.ad_headline)
val ad_description : TextView = itemView.findViewById(R.id.ad_description)
val ad_price : TextView = itemView.findViewById(R.id.ad_price)
val ad_store : TextView = itemView.findViewById(R.id.ad_store)
val call_to_action : CardView = itemView.findViewById(R.id.ad_call_to_action)
val ad_advertiser : TextView = itemView.findViewById(R.id.ad_advertiser)
val nativeAdView : NativeAdView = itemView.findViewById(R.id.nativeAdView)
fun createAD(context : Context){
val adLoader = AdLoader.Builder(context, context.getString(R.string.native_ad_id_test))
.forNativeAd { nativeAd ->
Log.d(TAG, "onNativeAdLoaded: ")
displayNativeAd(this#HolderNativeAd, nativeAd)
}.withNativeAdOptions(NativeAdOptions.Builder().build()).build()
adLoader.loadAd(AdRequest.Builder().build())
}
}
onCreateViewHolder
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder {
val view: View
if(viewType == VIEW_TYPE_CONTENT){
view = LayoutInflater.from(context2).inflate(R.layout.item_card, parent, false)
return HolderCards(view)
}else{
view = LayoutInflater.from(context2).inflate(R.layout.native_ad_card, parent, false)
return HolderNativeAd(view)
}
}
onBindViewHolder
override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
if (getItemViewType(position) == VIEW_TYPE_CONTENT) {
val model: Card = Cards[position]
(holder as HolderCards).setCard(model, context2)
} else if (getItemViewType(position) == VIEW_TYPE_AD) {
(holder as HolderNativeAd).createAD(context2)
}
}
getItemViewType
override fun getItemViewType(position: Int): Int {
//logic to display Native Ad between content
if(position != 0) {
return if (position % 2 == 0) {
//after 2 items, show native ad
VIEW_TYPE_AD
} else {
VIEW_TYPE_CONTENT
}
}
return VIEW_TYPE_CONTENT
}
And getitemCount() returns Cards.size
Cards mutable population:
currenctly I have a SingleValueEventListener which grabs the cards and puts them inside a mutableList calling adapter.NotifyItemInserted() for each item.
displayNativeAd (custom method used in the ad holder)
private fun displayNativeAd(holderNativeAd: CardAdapter.HolderNativeAd, nativeAd: NativeAd) {
/* Get Ad assets from the NativeAd Object */
val headline = nativeAd.headline
val body = nativeAd.body
val background = nativeAd.icon
val callToAction = nativeAd.callToAction
val price = nativeAd.price
val store = nativeAd.store
val advertiser = nativeAd.advertiser
...
... (checks to see if a val is null or not)
holderNativeAd.nativeAdView.setNativeAd(nativeAd)
}
All right buckle up because this is a long one! It's actually the "adding ads" part that's complicating things here, not the extra ViewHolder type.
You're missing items because you're replacing some of them with ads. The total number of items (itemCount) in your Adapter should be the number of cards plus the number of ads you want to display.
Because you're not handling that, you're effectively skipping over items in cards with this code:
override fun getItemViewType(position: Int): Int {
//logic to display Native Ad between content
if(position != 0) {
return if (position % 2 == 0) {
//after 2 items, show native ad
VIEW_TYPE_AD
} else {
VIEW_TYPE_CONTENT
}
}
return VIEW_TYPE_CONTENT
}
You have cards.size number of items, and instead of showing cards[2] you show an ad instead, and cards[2] never gets shown. (Also that code shows an ad every two items btw, position % 2 either produces a 0 or 1, so it loops every second number - you want position % 3 so it's every multiple of three. But there's more to it than that, we'll get to it!)
So you need logic to handle the fact that your data (cards) and your contents (cards + ads) are different:
itemCount needs to include the appropriate number of ads
getItemViewType needs to know if position holds an ad or a card
onBindViewHolder needs to be able to translate position to the appropriate index in cards when displaying a card
Let's lay down the rules first - let's say that you want an ad displayed as every third item, that starts after the first two items, and you're happy to end with an ad, to make things simple.
So the number of ads is just how many groups of 2 there are - integer division will do that:
val adCount = cards.size / 2
The total number of items is that plus the number of cards:
override fun getItemCount() = cards.size + (cards.size / 2)
Working out whether position is a card or an ad is simple enough, it's basically what you already did! Except we need to handle every third item as an ad. We also need to account for the zero-based indexing:
| | |
0 1 2 3 4 5 6 7 8 9
We get ads on 2, 5 and 8. We care about finding multiples of 3 (where the modulo operation returns zero) so we can add 1 to each position. This also eliminates the need to check if position == 0 (that special edge case was a sign your logic wasn't consistent - don't worry I only realised that while writing this!)
fun isCard(position: Int) = (position + 1) % 3 != 0
Note that we're using 3 here because we're dealing with the position in the list which has been padded out with an ad every 2 places. Every 2 items in cards has become 2+1 items in the adapter's content.
Really we should be using a constant, val ITEMS_PER_AD = 2 and deriving another value from that, val AD_FREQUENCY = ITEMS_PER_AD + 1. Avoids magic numbers that are hard to read and work with, and easy to mess up. This is clearer (maybe with better names!) and you can just change ITEMS_PER_AD to change how many there are, and everything else will adjust along with it
Translating from a position to a card is the last bit. You have to account for when a position isn't a valid card, i.e. isCard is false. It's easiest to return null here in that case.
It might help to look at how the translations should work out:
position: 0 1 2 3 4 5 6 7 8 9
card index: 0 1 x 2 3 x 4 5 x 6
Yep it's one of them logic puzzles - what's the pattern in this progression?
The offset is happening every multiple of 3 items, so what if we divide position by 3 and subtract it, removing those offsets?
position: 0 1 2 3 4 5 6 7 8 9
pos / 3: 0 0 0 1 1 1 2 2 2 3
card index: 0 1 x 2 3 x 4 5 x 6
Nice, that looks good! So now, we need to either return null if it's not a card, otherwise fetch the appropriate card from the data set:
fun getCardForPosition(position: Int): Card? {
val offset = position / 3
return if (isCard(position)) cards[position - offset] else null
}
Those are the pieces required to size your list properly, work out if a particular position is a card or an ad, and fetch the appropriate card from your data. Hopefully you can see how to work that into the Adapter methods to work out which itemViewType you need, etc.
You could actually just try to getCardForPosition in onBindViewHolder and if the result is null, display an ad (and cast the ViewHolder you've been passed to the ad one, since that's what you should be getting as they're all using the same functions to determine what's what). Lots of options, the logic around the list is the hard part!
As for the spaces, see if it works when you have everything displaying correctly. It might resolve itself, or it might be a layout issue with your ad items. Make sure their width isn't match_parent or anything. You can always use the Layout Inspector with a running app to see exactly what's happening in the layout on the screen, might give you some clues
I wanted to check I hadn't missed anything so I wrote a basic implementation if it helps:
data class Card(val info: String)
class Adapter(private val cards: List<Card>) : RecyclerView.Adapter<Adapter.MyViewHolder>() {
private fun isCard(position: Int) = (position + 1) % AD_FREQUENCY != 0
private fun getCardForPosition(position: Int): Card? {
val offset = position / AD_FREQUENCY
return if (isCard(position)) cards[position - offset] else null
}
override fun getItemViewType(position: Int) =
if (isCard(position)) CARD_VIEWTYPE else AD_VIEWTYPE
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): MyViewHolder {
val inflater = LayoutInflater.from(parent.context)
val binding = ItemViewBinding.inflate(inflater, parent, false)
return if (viewType == AD_VIEWTYPE) MyViewHolder.AdViewHolder(binding)
else MyViewHolder.CardViewHolder(binding)
}
override fun onBindViewHolder(holder: MyViewHolder, position: Int) {
val card = getCardForPosition(position)
if (card == null) (holder as MyViewHolder.AdViewHolder).binding.textView.text = "AD"
else (holder as MyViewHolder.CardViewHolder).binding.textView.text = card.info
}
override fun getItemCount() = cards.size + (cards.size / ITEMS_PER_AD)
sealed class MyViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
class AdViewHolder(val binding: ItemViewBinding) : MyViewHolder(binding.root)
class CardViewHolder(val binding: ItemViewBinding) : MyViewHolder(binding.root)
}
companion object {
const val ITEMS_PER_AD = 3
const val AD_FREQUENCY = ITEMS_PER_AD + 1
const val AD_VIEWTYPE = 0
const val CARD_VIEWTYPE = 1
}
}
// set up with
recycler.layoutManager =
LinearLayoutManager(requireContext(), LinearLayoutManager.HORIZONTAL, false)
recycler.adapter = Adapter(List(32) { Card("Content $it") })
Really simple, just uses the same layout for both ViewHolders with a TextView in it. Fixed size for the layout, no spaces popping up:
Hope it helps!
Yes this works fine, I have similar thing which can help too.
class MyVideoAdapter() :
RecyclerView.Adapter<RecyclerView.ViewHolder>() {
private val TAG = "AdsCalled"
companion object {
const val AD_DISPLAY_FREQUENCY = 3
const val ITEM_TYPE = 1
const val AD_TYPE = 0
}
private val adItems: MutableList<NativeAd>
init {
adItems = ArrayList()
}
private var myResult: MyResult? = null
set(value) {
field = value
notifyDataSetChanged()
}
private val itemList get() = myResult?.myVideos?.list?: emptyList()
class ItemHolder(val binding: ItemSingleVideoBinding) : RecyclerView.ViewHolder(binding.root)
class ItemAdHolder(val binding: ItemSingleVideoAdBinding) :
RecyclerView.ViewHolder(binding.root) {
init {
with(binding) {
nativeAdView.iconView = adAppIcon
nativeAdView.headlineView = adHeadline
nativeAdView.advertiserView = adAdvertiser
nativeAdView.priceView = adPrice
nativeAdView.storeView = adStore
}
}
}
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int) =
if (viewType == AD_TYPE)
ItemAdHolder(ItemSingleVideoAdBinding.inflate(
LayoutInflater
.from(parent.context), parent, false))
else
ItemHolder(ItemSingleVideoBinding.inflate(
LayoutInflater
.from(parent.context),parent,false))
override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
if (holder.itemViewType == AD_TYPE) {
val adHolder = holder as ItemAdHolder
var ad: NativeAd? = null
if (adItems.size > position / AD_DISPLAY_FREQUENCY) {
ad = adItems[position / AD_DISPLAY_FREQUENCY]
} else {
val nativeAdOptions =
NativeAdOptions.Builder().setMediaAspectRatio(MediaAspectRatio.LANDSCAPE)
.build()
val builder = AdLoader.Builder(adHolder.binding.root.context,
"ca-app-pub-3940256099942544/2247696110")
val adLoader: AdLoader = builder.forNativeAd { nativeAd ->
ad = nativeAd
adItems.add(nativeAd)
}.withNativeAdOptions(nativeAdOptions)
.withAdListener(object : AdListener() {
override fun onAdFailedToLoad(p0: LoadAdError) {
Log.d(TAG, "onAdFailedToLoad: Failed : ${p0.message}")
}
})
.build()
adLoader.loadAd(AdRequest.Builder().build())
}
ad?.let { nativeAd ->
adHolder.binding.run {
adHeadline.text = nativeAd.headline
adPrice.text = nativeAd.price
adStore.text = nativeAd.store
adAdvertiser.text = nativeAd.advertiser
adAppIcon.setImageDrawable(nativeAd.icon?.drawable)
nativeAdView.setNativeAd(nativeAd)
}
}
} else {
val index = position - position / AD_DISPLAY_FREQUENCY - 1
val item= itemList[index]
val itemHolder = holder as ItemHolder
}
}
}
}
override fun getItemCount() = (itemList.size + adItems.size)
override fun getItemViewType(position: Int): Int {
if (position % AD_DISPLAY_FREQUENCY == 0)
AD_TYPE
else ITEM_TYPE
}
fun clearResult() {
myResult = null
notifyDataSetChanged()
}
fun setResult(myResult : MyResult) {
this.myResult = myResult
notifyDataSetChanged()
}
}
But the main problem here is, what if the Admob failed to load the ads ?
If there's a condition when ads are not loading from the server at that time:
adsItem Size = 0
itemsList Size = 20 (Assume)
AD_DISPLAY_FREQUENCY = 3
So, after every 2 post an Ad will be displayed, and in getItemViewType method we have the modulas function (position%AD_FREQ..)
So. by default it will return the AD_TYPE and the AD Will not be loaded, resulting in empty ItemAdHolder layout inflation. Moreover we will skip the Post Item, as the size of adslist is 0 and we are updating the index for post items, so how to resolve this thing ? I tried checking the adItems size before getting viewType but it's not helping
What I have tried till now is
override fun getItemViewType(position: Int): Int {
return if (position == 0) 0 else
if (position % AD_DISPLAY_FREQUENCY == 0)
AD_TYPE
else ITEM_TYPE
}
override fun getItemCount() = if (itemList .isEmpty()) 0 else (itemList .size + adItems.size)
In bindViewHolder() for ITEM_TYPE case
val index = if (adItems.isNotEmpty()) position - position / AD_DISPLAY_FREQUENCY - 1 else position
I have tried this a few different ways and I havent been able to get this viewpager to perform correctly. I am setting a viewpager2 with an adapter but part of the requirements are that the viewpager be manually swipe-able as well the base on a button to increment the pager view. I have swiping and button click moving the view pager as intended however the autoscroll is something that is problematic.
I am setting a postDelayed runnable on the viewPager. The logs just done make sense when this is running you can see below for what the output looks like.
companion object {
private const val TAG = "LauncherActivity"
private const val timerDelay: Long = 10 * 1000 // 1 minute in milliseconds
var position: Int = 0
}
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
...
pager.autoScroll(timerDelay)
...
pager.registerOnPageChangeCallback(object : OnPageChangeCallback() {
override fun onPageSelected(position: Int) {
Log.d(TAG, "-> OnPageChangeCallback() -> position: ${position}")
super.onPageSelected(position)
if (position != LauncherActivity.position) LauncherActivity.position = position
}
})
}
fun ViewPager2.autoScroll(interval: Long) {
val count = adapter?.itemCount ?: 0
val handler = Handler()
val runnable = object: Runnable {
override fun run() {
if (position < count) {
Log.d(TAG, "Autoscroll: current position = ${position} ending position = ${position + 1}")
setCurrentItem((position++ % count), true)
Log.d(TAG, "New position: ${position}")
handler.postDelayed(this, interval)
}
}
}
handler.post(runnable)
}
The log to better explain whats happening
2020-05-22 11:42:51.485 D/LauncherActivity: Autoscroll: current position = 0 ending position = 1
2020-05-22 11:42:51.485 D/LauncherActivity: New position: 1
2020-05-22 11:42:51.621 D/LauncherActivity: -> OnPageChangeCallback() -> position: 0
This is initial load. The view is still showing position 0 in viewpager. Seems like the postDelayed ran but didnt run?
2020-05-22 11:43:01.492 D/LauncherActivity: Autoscroll: current position = 0 ending position = 1
2020-05-22 11:43:01.492 D/LauncherActivity: New position: 1
10 seconds later the post delayed runs again but doesnt actually change the viewpager. BUT it starts
everything off as it should. lack of OnPageChangeCallback() indicated it didnt change the view.
2020-05-22 11:43:11.497 D/LauncherActivity: Autoscroll: current position = 1 ending position = 2
2020-05-22 11:43:11.503 D/LauncherActivity: -> OnPageChangeCallback() -> position: 1
2020-05-22 11:43:11.506 D/LauncherActivity: New position: 1
The view finally changed to the next position
2020-05-22 11:43:21.518 D/LauncherActivity: Autoscroll: current position = 1 ending position = 2
2020-05-22 11:43:21.519 D/LauncherActivity: New position: 2
10 seconds later the post delayed runs again but doesnt actually change the viewpager.
2020-05-22 11:43:31.532 D/LauncherActivity: Autoscroll: current position = 2 ending position = 3
2020-05-22 11:43:31.534 D/LauncherActivity: -> OnPageChangeCallback() -> position: 2
2020-05-22 11:43:31.535 D/LauncherActivity: New position: 2
Finally it has changed to the final item.
2020-05-22 11:43:41.548 D/LauncherActivity: Autoscroll: current position = 2 ending position = 3
2020-05-22 11:43:41.550 D/LauncherActivity: New position: 3
Not a clue why it ran again...
With #Mwasz answer above this lead me back to workin on resolving the postDelayed pool problem when a user swipes forward or back or clicks a button to move forward. This is a complete solution as the onPageScrollStateSchanged indicated that a user physically swiped and the button onClick handles invalidating separately.
Edit: There is no need for onPageScrollStateChanged() callback. The handler callback can be cleared at the beginning of onPageSelected() with the same result.
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
val handler = Handler()
var origPosition: Int = 0
...
// pager.autoScroll(timerDelay)
...
pager.registerOnPageChangeCallback(object : OnPageChangeCallback() {
override fun onPageSelected(position: Int) {
super.onPageSelected(position)
handler.removeMessages(0)
val runnable = Runnable { pager.currentItem = ++pager.currentItem) }
if (position < pager.adapter?.itemCount ?: 0) {
handler.postDelayed(runnable, timerDelay)
}
}
...
btnContinue.setOnClickListener {
...
pager.currentItem = ++pager.currentItem
...
}
}
Only answer:
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
val handler = Handler()
var origPosition: Int = 0
...
// pager.autoScroll(timerDelay)
...
pager.registerOnPageChangeCallback(object : OnPageChangeCallback() {
override fun onPageSelected(position: Int) {
super.onPageSelected(position)
val runnable = Runnable { pager.setCurrentItem(position + 1) }
if (position < pager.adapter?.itemCount ?: 0) {
handler.postDelayed(runnable, timerDelay)
}
}
override fun onPageScrollStateChanged(state: Int) {
super.onPageScrollStateChanged(state)
/**
* The user swiped forward or back and we need to
* invalidate the previous handler.
*/
if (state == SCROLL_STATE_DRAGGING) handler.removeMessages(0)
}
})
...
btnContinue.setOnClickListener {
...
// We dont want the last delayed runnable jumping us back up the stack.
handler.removeMessages(0)
pager.setCurrentItem(++pager.currentItem)
...
}
}
I would delete the autoScroll(Long) method and do it like that:
At the end of registerOnPageChangeCallback's onPageSelected() add:
handler.postDelayed(pager.setCurrentItem(position + 1), timerDelay)
This way you will start your loop of scrolling the items.
pager.registerOnPageChangeCallback(object : OnPageChangeCallback() {
override fun onPageSelected(position: Int) {
Log.d(TAG, "-> OnPageChangeCallback() -> position: ${position}")
super.onPageSelected(position)
if (position != LauncherActivity.position) LauncherActivity.position = position
if (position < count) {
handler.postDelayed(pager.setCurrentItem(position + 1), timerDelay) // repeat
}
}
})
Also i don't know why do you use a remainder in
setCurrentItem((position++ % count)
It feels like it shouldn't be there.
I already tried this solution here, but unfortunately doesnt work in my scenario.
Ill keep it simple: I have multiple viewHolders with multiple animations for a chat App,
Since I have no touch listeners to register the adapter position of the typing indicators, I have:
In my CustomAdapter
private var typingIndicatorAdapterPosition: Int = -1
private var inlineErrorAdapterPosition: Int = -1
In my onBindViewHolder
override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
when (holder.itemViewType) {
...
USER_REQUEST_TEXT -> {
val userRequestViewHolder = (holder as UserRequestViewHolder)
configUserRequestViewHolder(userRequestViewHolder, position)
userRequestViewHolder.setIsRecyclable(false)
}
TYPE_INDICATOR -> {
val typingIndicatorViewHolder = (holder as TypingIndicatorViewHolder)
configTypingIndicatorViewHolder(typingIndicatorViewHolder, position)
typingIndicatorAdapterPosition = typingIndicatorViewHolder.layoutPosition
typingIndicatorViewHolder.setIsRecyclable(true)
}
INLINE_ERROR -> {
val inlineErrorViewHolder = (holder as InlineErrorViewHolder)
configInlineErrorViewHolder(inlineErrorViewHolder, position)
inlineErrorAdapterPosition = inlineErrorViewHolder.layoutPosition
inlineErrorViewHolder.setIsRecyclable(true)
}
}
}
my adapter code for deletion :
fun removeTypingIndicator() {
if(typingIndicatorAdapterPosition > 0) {
if(messageContainerList[typingIndicatorAdapterPosition].messageType == TYPE_INDICATOR) {
messageContainerList.removeAt(typingIndicatorAdapterPosition)
notifyItemRemoved(typingIndicatorAdapterPosition)
notifyItemRangeChanged(typingIndicatorAdapterPosition, itemCount - 1)
typingIndicatorAdapterPosition = -1
}
}
}
Note - I do not prefer notifyDataSetChanged() etc. as it cancels the animations.
here are some screen shots:
This line looks incorrect:
notifyItemRangeChanged(typingIndicatorAdapterPosition, itemCount - 1)
Assuming you're trying to change all the items from the typing indicator position through the end of the list, it looks like you're trying to use it as (start, end), but the parameters are actually (start, itemCount), with itemCount being the number of items changed at that index. See the documentation here for more information.
On a RecyclerView, I am able to suddenly scroll to the top of a selected item by using:
((LinearLayoutManager) recyclerView.getLayoutManager()).scrollToPositionWithOffset(position, 0);
However, this abruptly moves the item to the top position. I want to move to the top of an item smoothly.
I've also tried:
recyclerView.smoothScrollToPosition(position);
but it does not work well as it does not move the item to the position selected to the top. It merely scrolls the list until the item on the position is visible.
RecyclerView is designed to be extensible, so there is no need to subclass the LayoutManager (as droidev suggested) just to perform the scrolling.
Instead, just create a SmoothScroller with the preference SNAP_TO_START:
RecyclerView.SmoothScroller smoothScroller = new LinearSmoothScroller(context) {
#Override protected int getVerticalSnapPreference() {
return LinearSmoothScroller.SNAP_TO_START;
}
};
Now you set the position where you want to scroll to:
smoothScroller.setTargetPosition(position);
and pass that SmoothScroller to the LayoutManager:
layoutManager.startSmoothScroll(smoothScroller);
for this you have to create a custom LayoutManager
public class LinearLayoutManagerWithSmoothScroller extends LinearLayoutManager {
public LinearLayoutManagerWithSmoothScroller(Context context) {
super(context, VERTICAL, false);
}
public LinearLayoutManagerWithSmoothScroller(Context context, int orientation, boolean reverseLayout) {
super(context, orientation, reverseLayout);
}
#Override
public void smoothScrollToPosition(RecyclerView recyclerView, RecyclerView.State state,
int position) {
RecyclerView.SmoothScroller smoothScroller = new TopSnappedSmoothScroller(recyclerView.getContext());
smoothScroller.setTargetPosition(position);
startSmoothScroll(smoothScroller);
}
private class TopSnappedSmoothScroller extends LinearSmoothScroller {
public TopSnappedSmoothScroller(Context context) {
super(context);
}
#Override
public PointF computeScrollVectorForPosition(int targetPosition) {
return LinearLayoutManagerWithSmoothScroller.this
.computeScrollVectorForPosition(targetPosition);
}
#Override
protected int getVerticalSnapPreference() {
return SNAP_TO_START;
}
}
}
use this for your RecyclerView and call smoothScrollToPosition.
example :
recyclerView.setLayoutManager(new LinearLayoutManagerWithSmoothScroller(context));
recyclerView.smoothScrollToPosition(position);
this will scroll to top of the RecyclerView item of specified position.
This is an extension function I wrote in Kotlin to use with the RecyclerView (based on #Paul Woitaschek answer):
fun RecyclerView.smoothSnapToPosition(position: Int, snapMode: Int = LinearSmoothScroller.SNAP_TO_START) {
val smoothScroller = object : LinearSmoothScroller(this.context) {
override fun getVerticalSnapPreference(): Int = snapMode
override fun getHorizontalSnapPreference(): Int = snapMode
}
smoothScroller.targetPosition = position
layoutManager?.startSmoothScroll(smoothScroller)
}
Use it like this:
myRecyclerView.smoothSnapToPosition(itemPosition)
We can try like this
recyclerView.getLayoutManager().smoothScrollToPosition(recyclerView,new RecyclerView.State(), recyclerView.getAdapter().getItemCount());
Override the calculateDyToMakeVisible/calculateDxToMakeVisible function in LinearSmoothScroller to implement the offset Y/X position
override fun calculateDyToMakeVisible(view: View, snapPreference: Int): Int {
return super.calculateDyToMakeVisible(view, snapPreference) - ConvertUtils.dp2px(10f)
}
i Used Like This :
recyclerView.getLayoutManager().smoothScrollToPosition(recyclerView, new RecyclerView.State(), 5);
I want to more fully address the issue of scroll duration, which, should you choose any earlier answer, will in fact will vary dramatically (and unacceptably) according to the amount of scrolling necessary to reach the target position from the current position .
To obtain a uniform scroll duration the velocity (pixels per millisecond) must account for the size of each individual item - and when the items are of non-standard dimension then a whole new level of complexity is added.
This may be why the RecyclerView developers deployed the too-hard basket for this vital aspect of smooth scrolling.
Assuming that you want a semi-uniform scroll duration, and that your list contains semi-uniform items then you will need something like this.
/** Smoothly scroll to specified position allowing for interval specification. <br>
* Note crude deceleration towards end of scroll
* #param rv Your RecyclerView
* #param toPos Position to scroll to
* #param duration Approximate desired duration of scroll (ms)
* #throws IllegalArgumentException */
private static void smoothScroll(RecyclerView rv, int toPos, int duration) throws IllegalArgumentException {
int TARGET_SEEK_SCROLL_DISTANCE_PX = 10000; // See androidx.recyclerview.widget.LinearSmoothScroller
int itemHeight = rv.getChildAt(0).getHeight(); // Height of first visible view! NB: ViewGroup method!
itemHeight = itemHeight + 33; // Example pixel Adjustment for decoration?
int fvPos = ((LinearLayoutManager)rv.getLayoutManager()).findFirstCompletelyVisibleItemPosition();
int i = Math.abs((fvPos - toPos) * itemHeight);
if (i == 0) { i = (int) Math.abs(rv.getChildAt(0).getY()); }
final int totalPix = i; // Best guess: Total number of pixels to scroll
RecyclerView.SmoothScroller smoothScroller = new LinearSmoothScroller(rv.getContext()) {
#Override protected int getVerticalSnapPreference() {
return LinearSmoothScroller.SNAP_TO_START;
}
#Override protected int calculateTimeForScrolling(int dx) {
int ms = (int) ( duration * dx / (float)totalPix );
// Now double the interval for the last fling.
if (dx < TARGET_SEEK_SCROLL_DISTANCE_PX ) { ms = ms*2; } // Crude deceleration!
//lg(format("For dx=%d we allot %dms", dx, ms));
return ms;
}
};
//lg(format("Total pixels from = %d to %d = %d [ itemHeight=%dpix ]", fvPos, toPos, totalPix, itemHeight));
smoothScroller.setTargetPosition(toPos);
rv.getLayoutManager().startSmoothScroll(smoothScroller);
}
PS: I curse the day I began indiscriminately converting ListView to RecyclerView.
The easiest way I've found to scroll a RecyclerView is as follows:
// Define the Index we wish to scroll to.
final int lIndex = 0;
// Assign the RecyclerView's LayoutManager.
this.getRecyclerView().setLayoutManager(this.getLinearLayoutManager());
// Scroll the RecyclerView to the Index.
this.getLinearLayoutManager().smoothScrollToPosition(this.getRecyclerView(), new RecyclerView.State(), lIndex);
Thanks, #droidev for the solution. If anyone looking for Kotlin solution, refer this:
class LinearLayoutManagerWithSmoothScroller: LinearLayoutManager {
constructor(context: Context) : this(context, VERTICAL,false)
constructor(context: Context, orientation: Int, reverseValue: Boolean) : super(context, orientation, reverseValue)
override fun smoothScrollToPosition(recyclerView: RecyclerView?, state: RecyclerView.State?, position: Int) {
super.smoothScrollToPosition(recyclerView, state, position)
val smoothScroller = TopSnappedSmoothScroller(recyclerView?.context)
smoothScroller.targetPosition = position
startSmoothScroll(smoothScroller)
}
private class TopSnappedSmoothScroller(context: Context?) : LinearSmoothScroller(context){
var mContext = context
override fun computeScrollVectorForPosition(targetPosition: Int): PointF? {
return LinearLayoutManagerWithSmoothScroller(mContext as Context)
.computeScrollVectorForPosition(targetPosition)
}
override fun getVerticalSnapPreference(): Int {
return SNAP_TO_START
}
}
}
I have create an extension method based on position of items in a list which is bind with recycler view
Smooth scroll in large list takes longer time to scroll , use this to improve speed of scrolling and also have the smooth scroll animation. Cheers!!
fun RecyclerView?.perfectScroll(size: Int,up:Boolean = true ,smooth: Boolean = true) {
this?.apply {
if (size > 0) {
if (smooth) {
val minDirectScroll = 10 // left item to scroll
//smooth scroll
if (size > minDirectScroll) {
//scroll directly to certain position
val newSize = if (up) minDirectScroll else size - minDirectScroll
//scroll to new position
val newPos = newSize - 1
//direct scroll
scrollToPosition(newPos)
//smooth scroll to rest
perfectScroll(minDirectScroll, true)
} else {
//direct smooth scroll
smoothScrollToPosition(if (up) 0 else size-1)
}
} else {
//direct scroll
scrollToPosition(if (up) 0 else size-1)
}
}
} }
Just call the method anywhere using
rvList.perfectScroll(list.size,up=true,smooth=true)
Extend "LinearLayout" class and override the necessary functions
Create an instance of the above class in your fragment or activity
Call "recyclerView.smoothScrollToPosition(targetPosition)
CustomLinearLayout.kt :
class CustomLayoutManager(private val context: Context, layoutDirection: Int):
LinearLayoutManager(context, layoutDirection, false) {
companion object {
// This determines how smooth the scrolling will be
private
const val MILLISECONDS_PER_INCH = 300f
}
override fun smoothScrollToPosition(recyclerView: RecyclerView, state: RecyclerView.State, position: Int) {
val smoothScroller: LinearSmoothScroller = object: LinearSmoothScroller(context) {
fun dp2px(dpValue: Float): Int {
val scale = context.resources.displayMetrics.density
return (dpValue * scale + 0.5f).toInt()
}
// change this and the return super type to "calculateDyToMakeVisible" if the layout direction is set to VERTICAL
override fun calculateDxToMakeVisible(view: View ? , snapPreference : Int): Int {
return super.calculateDxToMakeVisible(view, SNAP_TO_END) - dp2px(50f)
}
//This controls the direction in which smoothScroll looks for your view
override fun computeScrollVectorForPosition(targetPosition: Int): PointF ? {
return this #CustomLayoutManager.computeScrollVectorForPosition(targetPosition)
}
//This returns the milliseconds it takes to scroll one pixel.
override fun calculateSpeedPerPixel(displayMetrics: DisplayMetrics): Float {
return MILLISECONDS_PER_INCH / displayMetrics.densityDpi
}
}
smoothScroller.targetPosition = position
startSmoothScroll(smoothScroller)
}
}
Note: The above example is set to HORIZONTAL direction, you can pass VERTICAL/HORIZONTAL during initialization.
If you set the direction to VERTICAL you should change the "calculateDxToMakeVisible" to "calculateDyToMakeVisible" (also mind the supertype call return value)
Activity/Fragment.kt :
...
smoothScrollerLayoutManager = CustomLayoutManager(context, LinearLayoutManager.HORIZONTAL)
recyclerView.layoutManager = smoothScrollerLayoutManager
.
.
.
fun onClick() {
// targetPosition passed from the adapter to activity/fragment
recyclerView.smoothScrollToPosition(targetPosition)
}
Here you can change to where you want to scroll, changing SNAP_TO_* return value in get**SnapPreference.
duration will be always used to scroll to the nearest item as well as the farthest item in your list.
on finish is used to do something when scrolling is almost finished.
fun RecyclerView.smoothScroll(toPos: Int, duration: Int = 500, onFinish: () -> Unit = {}) {
try {
val smoothScroller: RecyclerView.SmoothScroller = object : LinearSmoothScroller(context) {
override fun getVerticalSnapPreference(): Int {
return SNAP_TO_END
}
override fun calculateTimeForScrolling(dx: Int): Int {
return duration
}
override fun onStop() {
super.onStop()
onFinish.invoke()
}
}
smoothScroller.targetPosition = toPos
layoutManager?.startSmoothScroll(smoothScroller)
} catch (e: Exception) {
Timber.e("FAILED TO SMOOTH SCROLL: ${e.message}")
}
}
Probably #droidev approach is the correct one, but I just want to publish something a little bit different, which does basically the same job and doesn't require extension of the LayoutManager.
A NOTE here - this is gonna work well if your item (the one that you want to scroll on the top of the list) is visible on the screen and you just want to scroll it to the top automatically. It is useful when the last item in your list has some action, which adds new items in the same list and you want to focus the user on the new added items:
int recyclerViewTop = recyclerView.getTop();
int positionTop = recyclerView.findViewHolderForAdapterPosition(positionToScroll) != null ? recyclerView.findViewHolderForAdapterPosition(positionToScroll).itemView.getTop() : 200;
final int calcOffset = positionTop - recyclerViewTop;
//then the actual scroll is gonna happen with (x offset = 0) and (y offset = calcOffset)
recyclerView.scrollBy(0, offset);
The idea is simple:
1. We need to get the top coordinate of the recyclerview element;
2. We need to get the top coordinate of the view item that we want to scroll to the top;
3. At the end with the calculated offset we need to do
recyclerView.scrollBy(0, offset);
200 is just example hard coded integer value that you can use if the viewholder item doesn't exist, because that is possible as well.
You can reverse your list by list.reverse() and finaly call RecylerView.scrollToPosition(0)
list.reverse()
layout = LinearLayoutManager(this,LinearLayoutManager.VERTICAL,true)
RecylerView.scrollToPosition(0)