I'm trying to get two views to move to the middle of the screen and bounce back again x number of times.
This code does that but it runs only once.
` val view = findViewById(R.id.imageView2)
val animation = SpringAnimation(view, DynamicAnimation.TRANSLATION_Y, 0f)
val view2 = findViewById<View>(R.id.imageView3)
val animation2 = SpringAnimation(view2, DynamicAnimation.TRANSLATION_Y, 0f)
findViewById<View>(R.id.imageView2).also { img ->
SpringAnimation(img, DynamicAnimation.TRANSLATION_Y).apply {
animation.getSpring().setDampingRatio(SpringForce.DAMPING_RATIO_HIGH_BOUNCY)
animation.spring.stiffness = SpringForce.STIFFNESS_VERY_LOW
animation.animateToFinalPosition(50f)
}
}
findViewById<View>(R.id.imageView3).also { img ->
SpringAnimation(img, DynamicAnimation.TRANSLATION_Y).apply {
animation2.getSpring().setDampingRatio(SpringForce.DAMPING_RATIO_HIGH_BOUNCY)
animation2.spring.stiffness = SpringForce.STIFFNESS_VERY_LOW
animation2.animateToFinalPosition(-100f)
}
}`
So how do I get it to run x number of times?
This is obviously Spring Animation, but I'm not married to it. If there is another animation that would accomplish this I'd be totally open to changing.
You can run multiple SpringAnimations on the same View by repeatedly calling animateToFinalPosition(translation) with a sequence of translation values.
For example:
startSpringAnimations(findViewById<View>(R.id.imageView1), 300f, 6)
startSpringAnimations(findViewById<View>(R.id.imageView2), -600f, 6)
with a function
/**
* [view] will be moved using [times] SpringAnimations over a distance of abs([totalTranslation])
* If [totalTranslation] is negative, direction will be up, else down
*/
private fun startSpringAnimations(view: View, totalTranslation: Float, times: Int ) {
if(times <= 0){
return
}
val translation = totalTranslation/ times.toFloat()
SpringAnimation(view, DynamicAnimation.TRANSLATION_Y, 0f).apply{
spring.dampingRatio = SpringForce.DAMPING_RATIO_HIGH_BOUNCY
spring.stiffness = SpringForce.STIFFNESS_VERY_LOW
addEndListener(object: DynamicAnimation.OnAnimationEndListener{
private var count = 1
override fun onAnimationEnd(animation1: DynamicAnimation<*>?, canceled: Boolean, value: Float, velocity: Float) {
Log.d("SpringAnimation", "onAnimationEnd: animation $animation1 canceled $canceled value $value velocity $velocity count $count")
if (canceled) return
count++
if(count <= times){
animateToFinalPosition(translation * count)
}
}
})
animateToFinalPosition(translation)
}
}
Set android:repeatCount="infinite" in anim folder
I try to create an android game on pure kotlin, but I stacked on the bullet move rendering. If I do single shoot and will waiting that it disappear it works well, but if I moves player and do the next one shoot, previous shoot freeze on their position and doesn't finish their rendering. It looks like this:
On the picture: shooted once, moved left on the one point and do another shoot
Seems that the problem is in my drawShoot method. If the player position changed , that shoot position changed too, but I expect that coroutines will solved my problem, but it's isn't. Here is my code, any ideas hot to fix the bug?
Here is my code :
class GameV2 {
companion object {
private const val BLANK_CHAR = " "
private const val BLANK_CHAR_CODE = 0
private const val AREA_BORDER_CHAR = "x"
private const val AREA_BORDER_CHAR_CODE = 1
private const val PLAYER_ONE = "^"
private const val PLAYER_ONE_CODE = 2
private const val SHOOT = "o"
private const val SHOOT_CODE = 3
private var gameFinished = false
lateinit var gameAreaWidth: Number
lateinit var gameAreaHeigth: Number
private var gameArea = Array(0) { IntArray(0) }
private val observer = GameStateObserver()
private val gameState = GameState()
var shootPositionY: Int = 0
var shootPositionX: Int = 0
var playerPositionX: Int = 0
var playerPositionY: Int = 0
var bulletPlayerOnePositionX: Int = 0
var bulletPlayerOnePositionY: Int = 0
var bulletPlayerTwoPositionY: Int = 0
var bulletPlayerTwoPositionX: Int = 0
fun prepareGameEngine() {
observer.addObserver(gameState)
observer.changeState()
}
fun initGameArea(x: Int, y: Int) {
gameAreaWidth = y
gameAreaHeigth = x
gameArea = Array(x) { IntArray(y) }
var i = 1
var j: Int
while (i <= x) {
j = 1
while (j <= y) {
if (i == 1 || i == x || j == 1 || j == y) {
gameArea[i - 1][j - 1] = 1
} else {
gameArea[i - 1][j - 1] = 0
}
j++
}
i++
}
}
fun drawGameArea(): String {
val sb = StringBuffer()
gameArea.forEach { i ->
//println()
sb.append("\n")
i.forEach { j ->
if (j == BLANK_CHAR_CODE) {
// print(BLANK_CHAR)
sb.append(BLANK_CHAR)
}
if (j == AREA_BORDER_CHAR_CODE) {
// print(AREA_BORDER_CHAR)
sb.append(AREA_BORDER_CHAR)
}
if (j == PLAYER_ONE_CODE) {
// print(PLAYER_ONE)
sb.append(PLAYER_ONE)
}
if (j == SHOOT_CODE) {
// print(SHOOT)
sb.append(SHOOT)
}
}
}
return sb.toString()
}
private fun clearGameAreaSpaceInCoords(x: Int, y: Int) {
gameArea[x][y] = BLANK_CHAR_CODE
}
fun updateUserPosition(x: Int, y: Int) {
playerPositionX = x
playerPositionY = y
gameArea[playerPositionX][playerPositionY] = PLAYER_ONE_CODE
observer.changeState()
}
fun moveUserRight() {
if (playerPositionY < gameAreaWidth.toInt() - 2) {
// example: y - 1 = move left; x - 1 = move up
clearGameAreaSpaceInCoords(playerPositionX, playerPositionY)
updateUserPosition(playerPositionX, playerPositionY + 1)
}
}
fun moveUserLeft() {
if (playerPositionY > 1) {
clearGameAreaSpaceInCoords(playerPositionX, playerPositionY)
updateUserPosition(playerPositionX, playerPositionY - 1)
}
}
fun drawShoot() {
// playerPositionX - 1 mean that 1 point higher than player character
shootPositionY = playerPositionY
shootPositionX = playerPositionX
GlobalScope.launch { // launch a new coroutine in background and continue
for(i in 1..gameAreaHeigth.toInt() - 3 ){
gameArea[shootPositionX - i][shootPositionY] = SHOOT_CODE
observer.changeState()
delay(300L)
clearGameAreaSpaceInCoords(shootPositionX - i, shootPositionY)
observer.changeState()
}
}
}
private fun isGameStateChanged(): Boolean {
return GameStateObserver().hasChanged()
}
fun startGame() {
}
}
}
SOLVED. Solution : It's my bad. I call global variable inside drawShoot method. All what i need it's change global var to local, like this:
fun drawPlayerOneShoot() {
// playerOnePositionX - 1 mean that 1 point higher than player character
val shootPositionY = playerOnePositionY
val shootPositionX = playerOnePositionX
// launch a new coroutine in background and continue
GlobalScope.launch {
for(i in 1..gameAreaHeigth.toInt() - 3 ){
gameArea[shootPositionX - i][shootPositionY] = SHOOT_CODE
observer.changeState()
delay(300L)
clearGameAreaSpaceInCoords(shootPositionX - i, shootPositionY)
if (shootPositionX - i == playerTwoPositionX && shootPositionY == playerOnePositionY){
isPlayerOneWin = true
println("PLAYER ONE WIN")
}
observer.changeState()
}
}
}
From the first glimpse it seems that the problem lies not in the Coroutine itself, but inside of observer.changeState() . What kind of code is there? I guess it uses a singular "shot" instance and it does not matter whether you launch a new coroutine to change it.
I'm working on a grid interface (using VerticalGridSupportFragment) for Android TV and I'm looking for a way to allow users to move around items in the grid.
The idea is that the grid contains a number of TV channels and that the users should be able to change the order of the TV channels (sort / reorder). My proposed solution is to select a channel by clicking it. The channel then becomes "sticky" allowing you to move it around. When you're happy with the position, you click on the channel again, confirming its new position.
The obvious solution is to do something along the lines of this:
getVerticalGridView()?.let {
it.setOnChildSelectedListener { _, _, position, _ ->
// Move the item in the previous position to the new position
adapter.move(oldPosition, position)
// Set old position to currently selected position.
oldPosition = position
}
}
fun VerticalGridSupportFragment.getVerticalGridView(): VerticalGridView? {
return VerticalGridSupportFragment::class.java.getDeclaredField("mGridViewHolder")?.let {
it.isAccessible = true
return (it.get(this) as VerticalGridPresenter.ViewHolder).gridView
}
}
The problem with this is that adapter.move() causes another child selected event.
I've tried to circumvent this issue by temporarily removing the selection listener and instead keep a ObjectAdapter.DataObserver to notify me of onItemMoved() events, in which I set the selected position and once again set a selection listener.
This doesn't seem to work fully either.
It's not possible to use ItemTouchHelper as that was designed for touch purposes and not using a remote like we do on Android TV.
The official Android TV launcher app is doing something similar to what I need when you rearrange app shortcuts on the homescreen, but I can't think of a way to make it work.
Found a solution, which also appears to be what Google is using for the Android TV launcher.
In short: Create a custom VerticalGridView and override its focusSearch() method to determine how move / swap items.
Something similar to this:
class EditableVerticalGridView #JvmOverloads constructor(context: Context,
attrs: AttributeSet? = null,
defStyle: Int = 0) :
VerticalGridView(context, attrs, defStyle) {
override fun focusSearch(focused: View, direction: Int): View {
return if (focused.isSelected) {
swapItemsIfNeeded(focused, direction)
} else super.focusSearch(focused, direction)
}
private fun swapItemsIfNeeded(focused: View, direction: Int): View {
val position = getChildAdapterPosition(focused)
if (!itemAnimator.isRunning) {
if (canMoveInDirection(position, direction)) {
when (direction) {
FOCUS_LEFT -> moveChannel(position, position - 1)
FOCUS_UP -> moveChannel(position, position - NUM_COLUMN)
FOCUS_RIGHT -> moveChannel(position, position + 1)
FOCUS_DOWN -> moveChannel(position, position + NUM_COLUMN)
}
}
}
return focused
}
private fun canMoveInDirection(position: Int, direction: Int): Boolean {
when (direction) {
FOCUS_LEFT -> {
return position % NUM_COLUMN > 0
}
FOCUS_UP -> {
return position - NUM_COLUMN >= 0
}
FOCUS_RIGHT -> {
return !(position % NUM_COLUMN >= (NUM_COLUMN - 1) ||
position >= adapter.itemCount - 1)
}
FOCUS_DOWN -> {
return position + NUM_COLUMN <= adapter.itemCount - 1
}
else -> {
return false
}
}
}
private fun moveChannel(fromPosition: Int, toPosition: Int) {
(adapter as AllowedChannelAdapter).moveChannel(fromPosition, toPosition)
}
companion object {
private const val NUM_COLUMN: Int = 6
}
}
... and the moveChannel() function:
fun moveChannel(from: Int, to: Int) {
var offset = 1
if (from >= 0 && from <= channelItems.size - 1 && to >= 0 && to <= channelItems.size - 1) {
val fromItem = channelItems[from]
channelItems[from] = channelItems[to]
channelItems[to] = fromItem
notifyItemMoved(from, to)
val positionDifference = to - from
if (Math.abs(positionDifference) > 1) {
if (positionDifference > 0) {
offset = -1
}
notifyItemMoved(to + offset, from)
}
}
}
I use ViewPropertyAnimator for creating alpha animations. Both withStartAction() and withEndAction() work great, alpha values changed, but they changed in no time, looks like there is no animation, just changing values. Where is a mistake?
private fun run(millisecondsPerPixel: Long) { //millisPerPixel=30
pixelsToCenter = (_endHeight - _startHeight - emptyPlaceOffset) / 2.toLong() // 15
val duration = millisecondsPerPixel * pixelsToCenter // 450
val animator = if (opening) mainLayout!!.animate() else secondaryLayout!!.animate()
animator.alpha(0.0F).setDuration(duration)
.withStartAction {
changing = true
val resize = if (opening) ResizeAnimation(this#CustomToolbar, height, _endHeight) else
ResizeAnimation(this#CustomToolbar, height, _startHeight)
resize.duration = millisecondsPerPixel * (_endHeight - _startHeight)
startAnimation(resize) // this one works like a charm
}
.withEndAction {
val backAnimator = if (opening) {
mainLayout!!.visibility = View.GONE
secondaryLayout!!.animate()
} else {
secondaryLayout!!.visibility = View.GONE
mainLayout!!.animate()
}
backAnimator.alpha(1.0F).setDuration(duration)
.setStartDelay(millisecondsPerPixel * emptyPlaceOffset)
.withStartAction {
if (opening) secondaryLayout!!.visibility = View.VISIBLE else mainLayout!!.visibility = View.VISIBLE
}
.withEndAction { changing = false }
}
}
Background
It's possible to snap a RecyclerView to its center using :
LinearSnapHelper().attachToRecyclerView(recyclerView)
Example:
MainActivity.kt
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
val inflater = LayoutInflater.from(this)
recyclerView.adapter = object : RecyclerView.Adapter<RecyclerView.ViewHolder>() {
override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
val textView = holder.itemView as TextView
textView.setBackgroundColor(if (position % 2 == 0) 0xffff0000.toInt() else 0xff00ff00.toInt())
textView.text = position.toString()
}
override fun getItemCount(): Int {
return 100
}
override fun onCreateViewHolder(parent: ViewGroup?, viewType: Int): RecyclerView.ViewHolder {
val view = inflater.inflate(android.R.layout.simple_list_item_1, parent, false) as TextView
val cellSize = recyclerView.width / 3
view.layoutParams.height = cellSize
view.layoutParams.width = cellSize
view.gravity = Gravity.CENTER
return object : RecyclerView.ViewHolder(view) {}
}
}
LinearSnapHelper().attachToRecyclerView(recyclerView)
}
}
activity_main.xml
<android.support.v7.widget.RecyclerView
android:id="#+id/recyclerView" xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto" xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="horizontal"
app:layoutManager="android.support.v7.widget.LinearLayoutManager"/>
It's also possible to snap it to other sides, as was done in some libraries, such as here.
There are also libraries that allow to have a RecyclerView that can work like a ViewPager, such as here.
The problem
Supposed I have a RecyclerView (horizontal in my case) with many items, and I want that it will treat every X items (X is constant) as a single unit, and snap to each of those units.
For example, if I scroll a bit, it could snap to either the 0-item, or the X-item, but not to something in between them.
In a way, it's similar in its behavior to a case of a normal ViewPager, just that each page would have X items in it.
For example, if we continue from the sample code I wrote above,suppose X==3 , the snapping would be from this idle state:
to this idle state (in case we scrolled enough, otherwise would stay in previous state) :
Flinging or scrolling more should be handled like on ViewPager, just like the library I've mentioned above.
Scrolling more (in the same direction) to the next snapping point would be to reach item "6" , "9", and so on...
What I tried
I tried to search for alternative libraries, and I also tried to read the docs regarding this, but I didn't find anything that might be useful.
It might also be possible by using a ViewPager, but I think that's not the best way, because ViewPager doesn't recycle its items well, and I think it's less flexible than RecyclerView in terms of how to snap.
The questions
Is it possible to set RecyclerView to snap every X items, to treat each X items as a single page to snap to?
Of course, the items will take enough space for the whole RecyclerView, evenly.
Supposed it is possible, how would I get a callback when the RecyclerView is about to snap to a certain item, including having this item, before it got snapped? I ask this because it's related to the same question I asked here.
Kotlin solution
A working Kotlin solution based on "Cheticamp" answer (here), without the need to verify that you have the RecyclerView size, and with the choice of having a grid instead of a list, in the sample:
MainActivity.kt
class MainActivity : AppCompatActivity() {
val USE_GRID = false
// val USE_GRID = true
val ITEMS_PER_PAGE = 4
var selectedItemPos = 0
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
val inflater = LayoutInflater.from(this)
recyclerView.adapter = object : RecyclerView.Adapter<RecyclerView.ViewHolder>() {
override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
val textView = holder.itemView as TextView
textView.setBackgroundColor(if (position % 2 == 0) 0xffff0000.toInt() else 0xff00ff00.toInt())
textView.text = if (selectedItemPos == position) "selected: $position" else position.toString()
}
override fun getItemCount(): Int {
return 100
}
override fun onCreateViewHolder(parent: ViewGroup?, viewType: Int): RecyclerView.ViewHolder {
val view = inflater.inflate(android.R.layout.simple_list_item_1, parent, false) as TextView
view.layoutParams.width = if (USE_GRID)
recyclerView.width / (ITEMS_PER_PAGE / 2)
else
recyclerView.width / 4
view.layoutParams.height = recyclerView.height / (ITEMS_PER_PAGE / 2)
view.gravity = Gravity.CENTER
return object : RecyclerView.ViewHolder(view) {
}
}
}
recyclerView.layoutManager = if (USE_GRID)
GridLayoutManager(this, ITEMS_PER_PAGE / 2, GridLayoutManager.HORIZONTAL, false)
else
LinearLayoutManager(this, LinearLayoutManager.HORIZONTAL, false)
val snapToBlock = SnapToBlock(recyclerView, ITEMS_PER_PAGE)
snapToBlock.attachToRecyclerView(recyclerView)
snapToBlock.setSnapBlockCallback(object : SnapToBlock.SnapBlockCallback {
override fun onBlockSnap(snapPosition: Int) {
if (selectedItemPos == snapPosition)
return
selectedItemPos = snapPosition
recyclerView.adapter.notifyDataSetChanged()
}
override fun onBlockSnapped(snapPosition: Int) {
if (selectedItemPos == snapPosition)
return
selectedItemPos = snapPosition
recyclerView.adapter.notifyDataSetChanged()
}
})
}
}
SnapToBlock.kt
/**#param maxFlingBlocks Maxim blocks to move during most vigorous fling*/
class SnapToBlock constructor(private val maxFlingBlocks: Int) : SnapHelper() {
private var recyclerView: RecyclerView? = null
// Total number of items in a block of view in the RecyclerView
private var blocksize: Int = 0
// Maximum number of positions to move on a fling.
private var maxPositionsToMove: Int = 0
// Width of a RecyclerView item if orientation is horizonal; height of the item if vertical
private var itemDimension: Int = 0
// Callback interface when blocks are snapped.
private var snapBlockCallback: SnapBlockCallback? = null
// When snapping, used to determine direction of snap.
private var priorFirstPosition = RecyclerView.NO_POSITION
// Our private scroller
private var scroller: Scroller? = null
// Horizontal/vertical layout helper
private var orientationHelper: OrientationHelper? = null
// LTR/RTL helper
private var layoutDirectionHelper: LayoutDirectionHelper? = null
#Throws(IllegalStateException::class)
override fun attachToRecyclerView(recyclerView: RecyclerView?) {
if (recyclerView != null) {
this.recyclerView = recyclerView
val layoutManager = recyclerView.layoutManager as LinearLayoutManager
orientationHelper = when {
layoutManager.canScrollHorizontally() -> OrientationHelper.createHorizontalHelper(layoutManager)
layoutManager.canScrollVertically() -> OrientationHelper.createVerticalHelper(layoutManager)
else -> throw IllegalStateException("RecyclerView must be scrollable")
}
scroller = Scroller(this.recyclerView!!.context, sInterpolator)
initItemDimensionIfNeeded(layoutManager)
}
super.attachToRecyclerView(recyclerView)
}
// Called when the target view is available and we need to know how much more
// to scroll to get it lined up with the side of the RecyclerView.
override fun calculateDistanceToFinalSnap(layoutManager: RecyclerView.LayoutManager, targetView: View): IntArray {
val out = IntArray(2)
initLayoutDirectionHelperIfNeeded(layoutManager)
if (layoutManager.canScrollHorizontally())
out[0] = layoutDirectionHelper!!.getScrollToAlignView(targetView)
if (layoutManager.canScrollVertically())
out[1] = layoutDirectionHelper!!.getScrollToAlignView(targetView)
if (snapBlockCallback != null)
if (out[0] == 0 && out[1] == 0)
snapBlockCallback!!.onBlockSnapped(layoutManager.getPosition(targetView))
else
snapBlockCallback!!.onBlockSnap(layoutManager.getPosition(targetView))
return out
}
private fun initLayoutDirectionHelperIfNeeded(layoutManager: RecyclerView.LayoutManager) {
if (layoutDirectionHelper == null)
if (layoutManager.canScrollHorizontally())
layoutDirectionHelper = LayoutDirectionHelper()
else if (layoutManager.canScrollVertically())
// RTL doesn't matter for vertical scrolling for this class.
layoutDirectionHelper = LayoutDirectionHelper(false)
}
// We are flinging and need to know where we are heading.
override fun findTargetSnapPosition(layoutManager: RecyclerView.LayoutManager, velocityX: Int, velocityY: Int): Int {
initLayoutDirectionHelperIfNeeded(layoutManager)
val lm = layoutManager as LinearLayoutManager
initItemDimensionIfNeeded(layoutManager)
scroller!!.fling(0, 0, velocityX, velocityY, Integer.MIN_VALUE, Integer.MAX_VALUE, Integer.MIN_VALUE, Integer.MAX_VALUE)
return when {
velocityX != 0 -> layoutDirectionHelper!!.getPositionsToMove(lm, scroller!!.finalX, itemDimension)
else -> if (velocityY != 0)
layoutDirectionHelper!!.getPositionsToMove(lm, scroller!!.finalY, itemDimension)
else RecyclerView.NO_POSITION
}
}
// We have scrolled to the neighborhood where we will snap. Determine the snap position.
override fun findSnapView(layoutManager: RecyclerView.LayoutManager): View? {
// Snap to a view that is either 1) toward the bottom of the data and therefore on screen,
// or, 2) toward the top of the data and may be off-screen.
val snapPos = calcTargetPosition(layoutManager as LinearLayoutManager)
val snapView = if (snapPos == RecyclerView.NO_POSITION)
null
else
layoutManager.findViewByPosition(snapPos)
if (snapView == null)
Log.d(TAG, "<<<<findSnapView is returning null!")
Log.d(TAG, "<<<<findSnapView snapos=" + snapPos)
return snapView
}
// Does the heavy lifting for findSnapView.
private fun calcTargetPosition(layoutManager: LinearLayoutManager): Int {
val snapPos: Int
initLayoutDirectionHelperIfNeeded(layoutManager)
val firstVisiblePos = layoutManager.findFirstVisibleItemPosition()
if (firstVisiblePos == RecyclerView.NO_POSITION)
return RecyclerView.NO_POSITION
initItemDimensionIfNeeded(layoutManager)
if (firstVisiblePos >= priorFirstPosition) {
// Scrolling toward bottom of data
val firstCompletePosition = layoutManager.findFirstCompletelyVisibleItemPosition()
snapPos = if (firstCompletePosition != RecyclerView.NO_POSITION && firstCompletePosition % blocksize == 0)
firstCompletePosition
else
roundDownToBlockSize(firstVisiblePos + blocksize)
} else {
// Scrolling toward top of data
snapPos = roundDownToBlockSize(firstVisiblePos)
// Check to see if target view exists. If it doesn't, force a smooth scroll.
// SnapHelper only snaps to existing views and will not scroll to a non-existant one.
// If limiting fling to single block, then the following is not needed since the
// views are likely to be in the RecyclerView pool.
if (layoutManager.findViewByPosition(snapPos) == null) {
val toScroll = layoutDirectionHelper!!.calculateDistanceToScroll(layoutManager, snapPos)
recyclerView!!.smoothScrollBy(toScroll[0], toScroll[1], sInterpolator)
}
}
priorFirstPosition = firstVisiblePos
return snapPos
}
private fun initItemDimensionIfNeeded(layoutManager: RecyclerView.LayoutManager) {
if (itemDimension != 0)
return
val child = layoutManager.getChildAt(0) ?: return
if (layoutManager.canScrollHorizontally()) {
itemDimension = child.width
blocksize = getSpanCount(layoutManager) * (recyclerView!!.width / itemDimension)
} else if (layoutManager.canScrollVertically()) {
itemDimension = child.height
blocksize = getSpanCount(layoutManager) * (recyclerView!!.height / itemDimension)
}
maxPositionsToMove = blocksize * maxFlingBlocks
}
private fun getSpanCount(layoutManager: RecyclerView.LayoutManager): Int = (layoutManager as? GridLayoutManager)?.spanCount ?: 1
private fun roundDownToBlockSize(trialPosition: Int): Int = trialPosition - trialPosition % blocksize
private fun roundUpToBlockSize(trialPosition: Int): Int = roundDownToBlockSize(trialPosition + blocksize - 1)
override fun createScroller(layoutManager: RecyclerView.LayoutManager): LinearSmoothScroller? {
return if (layoutManager !is RecyclerView.SmoothScroller.ScrollVectorProvider)
null
else object : LinearSmoothScroller(recyclerView!!.context) {
override fun onTargetFound(targetView: View, state: RecyclerView.State?, action: RecyclerView.SmoothScroller.Action) {
val snapDistances = calculateDistanceToFinalSnap(recyclerView!!.layoutManager, targetView)
val dx = snapDistances[0]
val dy = snapDistances[1]
val time = calculateTimeForDeceleration(Math.max(Math.abs(dx), Math.abs(dy)))
if (time > 0)
action.update(dx, dy, time, sInterpolator)
}
override fun calculateSpeedPerPixel(displayMetrics: DisplayMetrics): Float = MILLISECONDS_PER_INCH / displayMetrics.densityDpi
}
}
fun setSnapBlockCallback(callback: SnapBlockCallback?) {
snapBlockCallback = callback
}
/*
Helper class that handles calculations for LTR and RTL layouts.
*/
private inner class LayoutDirectionHelper {
// Is the layout an RTL one?
private val mIsRTL: Boolean
constructor() {
mIsRTL = ViewCompat.getLayoutDirection(recyclerView) == ViewCompat.LAYOUT_DIRECTION_RTL
}
constructor(isRTL: Boolean) {
mIsRTL = isRTL
}
/*
Calculate the amount of scroll needed to align the target view with the layout edge.
*/
fun getScrollToAlignView(targetView: View): Int = if (mIsRTL)
orientationHelper!!.getDecoratedEnd(targetView) - recyclerView!!.width
else
orientationHelper!!.getDecoratedStart(targetView)
/**
* Calculate the distance to final snap position when the view corresponding to the snap
* position is not currently available.
*
* #param layoutManager LinearLayoutManager or descendent class
* #param targetPos - Adapter position to snap to
* #return int[2] {x-distance in pixels, y-distance in pixels}
*/
fun calculateDistanceToScroll(layoutManager: LinearLayoutManager, targetPos: Int): IntArray {
val out = IntArray(2)
val firstVisiblePos = layoutManager.findFirstVisibleItemPosition()
if (layoutManager.canScrollHorizontally()) {
if (targetPos <= firstVisiblePos) // scrolling toward top of data
if (mIsRTL) {
val lastView = layoutManager.findViewByPosition(layoutManager.findLastVisibleItemPosition())
out[0] = orientationHelper!!.getDecoratedEnd(lastView) + (firstVisiblePos - targetPos) * itemDimension
} else {
val firstView = layoutManager.findViewByPosition(firstVisiblePos)
out[0] = orientationHelper!!.getDecoratedStart(firstView) - (firstVisiblePos - targetPos) * itemDimension
}
}
if (layoutManager.canScrollVertically() && targetPos <= firstVisiblePos) { // scrolling toward top of data
val firstView = layoutManager.findViewByPosition(firstVisiblePos)
out[1] = firstView.top - (firstVisiblePos - targetPos) * itemDimension
}
return out
}
/*
Calculate the number of positions to move in the RecyclerView given a scroll amount
and the size of the items to be scrolled. Return integral multiple of mBlockSize not
equal to zero.
*/
fun getPositionsToMove(llm: LinearLayoutManager, scroll: Int, itemSize: Int): Int {
var positionsToMove: Int
positionsToMove = roundUpToBlockSize(Math.abs(scroll) / itemSize)
if (positionsToMove < blocksize)
// Must move at least one block
positionsToMove = blocksize
else if (positionsToMove > maxPositionsToMove)
// Clamp number of positions to move so we don't get wild flinging.
positionsToMove = maxPositionsToMove
if (scroll < 0)
positionsToMove *= -1
if (mIsRTL)
positionsToMove *= -1
return if (layoutDirectionHelper!!.isDirectionToBottom(scroll < 0)) {
// Scrolling toward the bottom of data.
roundDownToBlockSize(llm.findFirstVisibleItemPosition()) + positionsToMove
} else roundDownToBlockSize(llm.findLastVisibleItemPosition()) + positionsToMove
// Scrolling toward the top of the data.
}
fun isDirectionToBottom(velocityNegative: Boolean): Boolean = if (mIsRTL) velocityNegative else !velocityNegative
}
interface SnapBlockCallback {
fun onBlockSnap(snapPosition: Int)
fun onBlockSnapped(snapPosition: Int)
}
companion object {
// Borrowed from ViewPager.java
private val sInterpolator = Interpolator { input ->
var t = input
// _o(t) = t * t * ((tension + 1) * t + tension)
// o(t) = _o(t - 1) + 1
t -= 1.0f
t * t * t + 1.0f
}
private val MILLISECONDS_PER_INCH = 100f
private val TAG = "SnapToBlock"
}
}
Update
Even though I've marked an answer as accepted, as it works fine, I've noticed it has serious issues:
Smooth scrolling doesn't seem to work fine (doesn't scroll to correct place). Only scrolling that work is as such (but with the "smearing" effect) :
(recyclerView.layoutManager as LinearLayoutManager).scrollToPositionWithOffset(targetPos,0)
When switching to RTL (Right to left) locale such as Hebrew ("עברית"), it doesn't let me scroll at all.
I've noticed that onCreateViewHolder is called a lot. In fact it is called every time I scroll, even for times it should have recycled the ViewHolders. This means there is an excessive creation of views, and it might also mean there is a memory leak.
I've tried to fix those myself, but failed so far.
If anyone here knows how to fix it, I will grant the extra, new bounty
Update: as we got a fix for RTL/LTR, I've updated the Kotlin solution within this post.
Update: about point #3 , this seems to be because there is a pool of views for the recyclerView, which gets filled too soon. To handle this, we can simply enlarge the pool size, by using recyclerView.getRecycledViewPool() .setMaxRecycledViews(viewType, Integer.MAX_VALUE) for each view type we have in it. Weird thing that this is really needed. I've posted about it to Google (here and here) but was rejected that the pool should be unlimited by default. In the end, I decided to at least request to have a more convinient function to do it for all view types (here).
SnapHelper supplies the necessary framework for what you are attempting, but it needs to be extended to handle blocks of views. The class SnapToBlock below extends SnapHelper to snap to blocks of views. In the example, I have used four views to a block but it can be more or less.
Update: The code has been change to accommodate GridLayoutManager as well as LinearLayoutManager. Flinging is now inhibited so the snapping works more list a ViewPager. Horizontal and vertical scrolling is now supported as well as LTR and RTL layouts.
Update: Changed smooth scroll interpolator to be more like ViewPager.
Update: Adding callbacks for pre/post snapping.
Update: Adding support for RTL layouts.
Here is a quick video of the sample app:
Set up the layout manager as follows:
// For LinearLayoutManager horizontal orientation
recyclerView.setLayoutManager(new LinearLayoutManager(this, RecyclerView.HORIZONTAL, false));
// For GridLayoutManager vertical orientation
recyclerView.setLayoutManager(new GridLayoutManager(this, SPAN_COUNT, RecyclerView.VERTICAL, false));
Add the following to attach the SnapToBlock to the RecyclerView.
SnapToBlock snapToBlock = new SnapToBlock(mMaxFlingPages);
snapToBlock.attachToRecyclerView(recyclerView);
mMaxFlingPages is the maximum number of blocks (rowsCols * spans) to allow to be flung at one time.
For call backs when a snap is about to be made and has been completed, add the following:
snapToBlock.setSnapBlockCallback(new SnapToBlock.SnapBlockCallback() {
#Override
public void onBlockSnap(int snapPosition) {
...
}
#Override
public void onBlockSnapped(int snapPosition) {
...
}
});
SnapToBlock.java
/* The number of items in the RecyclerView should be a multiple of block size; otherwise, the
extra item views will not be positioned on a block boundary when the end of the data is reached.
Pad out with empty item views if needed.
Updated to accommodate RTL layouts.
*/
public class SnapToBlock extends SnapHelper {
private RecyclerView mRecyclerView;
// Total number of items in a block of view in the RecyclerView
private int mBlocksize;
// Maximum number of positions to move on a fling.
private int mMaxPositionsToMove;
// Width of a RecyclerView item if orientation is horizonal; height of the item if vertical
private int mItemDimension;
// Maxim blocks to move during most vigorous fling.
private final int mMaxFlingBlocks;
// Callback interface when blocks are snapped.
private SnapBlockCallback mSnapBlockCallback;
// When snapping, used to determine direction of snap.
private int mPriorFirstPosition = RecyclerView.NO_POSITION;
// Our private scroller
private Scroller mScroller;
// Horizontal/vertical layout helper
private OrientationHelper mOrientationHelper;
// LTR/RTL helper
private LayoutDirectionHelper mLayoutDirectionHelper;
// Borrowed from ViewPager.java
private static final Interpolator sInterpolator = new Interpolator() {
public float getInterpolation(float t) {
// _o(t) = t * t * ((tension + 1) * t + tension)
// o(t) = _o(t - 1) + 1
t -= 1.0f;
return t * t * t + 1.0f;
}
};
SnapToBlock(int maxFlingBlocks) {
super();
mMaxFlingBlocks = maxFlingBlocks;
}
#Override
public void attachToRecyclerView(#Nullable final RecyclerView recyclerView)
throws IllegalStateException {
if (recyclerView != null) {
mRecyclerView = recyclerView;
final LinearLayoutManager layoutManager =
(LinearLayoutManager) recyclerView.getLayoutManager();
if (layoutManager.canScrollHorizontally()) {
mOrientationHelper = OrientationHelper.createHorizontalHelper(layoutManager);
mLayoutDirectionHelper =
new LayoutDirectionHelper(ViewCompat.getLayoutDirection(mRecyclerView));
} else if (layoutManager.canScrollVertically()) {
mOrientationHelper = OrientationHelper.createVerticalHelper(layoutManager);
// RTL doesn't matter for vertical scrolling for this class.
mLayoutDirectionHelper = new LayoutDirectionHelper(RecyclerView.LAYOUT_DIRECTION_LTR);
} else {
throw new IllegalStateException("RecyclerView must be scrollable");
}
mScroller = new Scroller(mRecyclerView.getContext(), sInterpolator);
initItemDimensionIfNeeded(layoutManager);
}
super.attachToRecyclerView(recyclerView);
}
// Called when the target view is available and we need to know how much more
// to scroll to get it lined up with the side of the RecyclerView.
#NonNull
#Override
public int[] calculateDistanceToFinalSnap(#NonNull RecyclerView.LayoutManager layoutManager,
#NonNull View targetView) {
int[] out = new int[2];
if (layoutManager.canScrollHorizontally()) {
out[0] = mLayoutDirectionHelper.getScrollToAlignView(targetView);
}
if (layoutManager.canScrollVertically()) {
out[1] = mLayoutDirectionHelper.getScrollToAlignView(targetView);
}
if (mSnapBlockCallback != null) {
if (out[0] == 0 && out[1] == 0) {
mSnapBlockCallback.onBlockSnapped(layoutManager.getPosition(targetView));
} else {
mSnapBlockCallback.onBlockSnap(layoutManager.getPosition(targetView));
}
}
return out;
}
// We are flinging and need to know where we are heading.
#Override
public int findTargetSnapPosition(RecyclerView.LayoutManager layoutManager,
int velocityX, int velocityY) {
LinearLayoutManager lm = (LinearLayoutManager) layoutManager;
initItemDimensionIfNeeded(layoutManager);
mScroller.fling(0, 0, velocityX, velocityY, Integer.MIN_VALUE, Integer.MAX_VALUE,
Integer.MIN_VALUE, Integer.MAX_VALUE);
if (velocityX != 0) {
return mLayoutDirectionHelper
.getPositionsToMove(lm, mScroller.getFinalX(), mItemDimension);
}
if (velocityY != 0) {
return mLayoutDirectionHelper
.getPositionsToMove(lm, mScroller.getFinalY(), mItemDimension);
}
return RecyclerView.NO_POSITION;
}
// We have scrolled to the neighborhood where we will snap. Determine the snap position.
#Override
public View findSnapView(RecyclerView.LayoutManager layoutManager) {
// Snap to a view that is either 1) toward the bottom of the data and therefore on screen,
// or, 2) toward the top of the data and may be off-screen.
int snapPos = calcTargetPosition((LinearLayoutManager) layoutManager);
View snapView = (snapPos == RecyclerView.NO_POSITION)
? null : layoutManager.findViewByPosition(snapPos);
if (snapView == null) {
Log.d(TAG, "<<<<findSnapView is returning null!");
}
Log.d(TAG, "<<<<findSnapView snapos=" + snapPos);
return snapView;
}
// Does the heavy lifting for findSnapView.
private int calcTargetPosition(LinearLayoutManager layoutManager) {
int snapPos;
int firstVisiblePos = layoutManager.findFirstVisibleItemPosition();
if (firstVisiblePos == RecyclerView.NO_POSITION) {
return RecyclerView.NO_POSITION;
}
initItemDimensionIfNeeded(layoutManager);
if (firstVisiblePos >= mPriorFirstPosition) {
// Scrolling toward bottom of data
int firstCompletePosition = layoutManager.findFirstCompletelyVisibleItemPosition();
if (firstCompletePosition != RecyclerView.NO_POSITION
&& firstCompletePosition % mBlocksize == 0) {
snapPos = firstCompletePosition;
} else {
snapPos = roundDownToBlockSize(firstVisiblePos + mBlocksize);
}
} else {
// Scrolling toward top of data
snapPos = roundDownToBlockSize(firstVisiblePos);
// Check to see if target view exists. If it doesn't, force a smooth scroll.
// SnapHelper only snaps to existing views and will not scroll to a non-existant one.
// If limiting fling to single block, then the following is not needed since the
// views are likely to be in the RecyclerView pool.
if (layoutManager.findViewByPosition(snapPos) == null) {
int[] toScroll = mLayoutDirectionHelper.calculateDistanceToScroll(layoutManager, snapPos);
mRecyclerView.smoothScrollBy(toScroll[0], toScroll[1], sInterpolator);
}
}
mPriorFirstPosition = firstVisiblePos;
return snapPos;
}
private void initItemDimensionIfNeeded(final RecyclerView.LayoutManager layoutManager) {
if (mItemDimension != 0) {
return;
}
View child;
if ((child = layoutManager.getChildAt(0)) == null) {
return;
}
if (layoutManager.canScrollHorizontally()) {
mItemDimension = child.getWidth();
mBlocksize = getSpanCount(layoutManager) * (mRecyclerView.getWidth() / mItemDimension);
} else if (layoutManager.canScrollVertically()) {
mItemDimension = child.getHeight();
mBlocksize = getSpanCount(layoutManager) * (mRecyclerView.getHeight() / mItemDimension);
}
mMaxPositionsToMove = mBlocksize * mMaxFlingBlocks;
}
private int getSpanCount(RecyclerView.LayoutManager layoutManager) {
return (layoutManager instanceof GridLayoutManager)
? ((GridLayoutManager) layoutManager).getSpanCount()
: 1;
}
private int roundDownToBlockSize(int trialPosition) {
return trialPosition - trialPosition % mBlocksize;
}
private int roundUpToBlockSize(int trialPosition) {
return roundDownToBlockSize(trialPosition + mBlocksize - 1);
}
#Nullable
protected LinearSmoothScroller createScroller(RecyclerView.LayoutManager layoutManager) {
if (!(layoutManager instanceof RecyclerView.SmoothScroller.ScrollVectorProvider)) {
return null;
}
return new LinearSmoothScroller(mRecyclerView.getContext()) {
#Override
protected void onTargetFound(View targetView, RecyclerView.State state, Action action) {
int[] snapDistances = calculateDistanceToFinalSnap(mRecyclerView.getLayoutManager(),
targetView);
final int dx = snapDistances[0];
final int dy = snapDistances[1];
final int time = calculateTimeForDeceleration(Math.max(Math.abs(dx), Math.abs(dy)));
if (time > 0) {
action.update(dx, dy, time, sInterpolator);
}
}
#Override
protected float calculateSpeedPerPixel(DisplayMetrics displayMetrics) {
return MILLISECONDS_PER_INCH / displayMetrics.densityDpi;
}
};
}
public void setSnapBlockCallback(#Nullable SnapBlockCallback callback) {
mSnapBlockCallback = callback;
}
/*
Helper class that handles calculations for LTR and RTL layouts.
*/
private class LayoutDirectionHelper {
// Is the layout an RTL one?
private final boolean mIsRTL;
#TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR1)
LayoutDirectionHelper(int direction) {
mIsRTL = direction == View.LAYOUT_DIRECTION_RTL;
}
/*
Calculate the amount of scroll needed to align the target view with the layout edge.
*/
int getScrollToAlignView(View targetView) {
return (mIsRTL)
? mOrientationHelper.getDecoratedEnd(targetView) - mRecyclerView.getWidth()
: mOrientationHelper.getDecoratedStart(targetView);
}
/**
* Calculate the distance to final snap position when the view corresponding to the snap
* position is not currently available.
*
* #param layoutManager LinearLayoutManager or descendent class
* #param targetPos - Adapter position to snap to
* #return int[2] {x-distance in pixels, y-distance in pixels}
*/
int[] calculateDistanceToScroll(LinearLayoutManager layoutManager, int targetPos) {
int[] out = new int[2];
int firstVisiblePos;
firstVisiblePos = layoutManager.findFirstVisibleItemPosition();
if (layoutManager.canScrollHorizontally()) {
if (targetPos <= firstVisiblePos) { // scrolling toward top of data
if (mIsRTL) {
View lastView = layoutManager.findViewByPosition(layoutManager.findLastVisibleItemPosition());
out[0] = mOrientationHelper.getDecoratedEnd(lastView)
+ (firstVisiblePos - targetPos) * mItemDimension;
} else {
View firstView = layoutManager.findViewByPosition(firstVisiblePos);
out[0] = mOrientationHelper.getDecoratedStart(firstView)
- (firstVisiblePos - targetPos) * mItemDimension;
}
}
}
if (layoutManager.canScrollVertically()) {
if (targetPos <= firstVisiblePos) { // scrolling toward top of data
View firstView = layoutManager.findViewByPosition(firstVisiblePos);
out[1] = firstView.getTop() - (firstVisiblePos - targetPos) * mItemDimension;
}
}
return out;
}
/*
Calculate the number of positions to move in the RecyclerView given a scroll amount
and the size of the items to be scrolled. Return integral multiple of mBlockSize not
equal to zero.
*/
int getPositionsToMove(LinearLayoutManager llm, int scroll, int itemSize) {
int positionsToMove;
positionsToMove = roundUpToBlockSize(Math.abs(scroll) / itemSize);
if (positionsToMove < mBlocksize) {
// Must move at least one block
positionsToMove = mBlocksize;
} else if (positionsToMove > mMaxPositionsToMove) {
// Clamp number of positions to move so we don't get wild flinging.
positionsToMove = mMaxPositionsToMove;
}
if (scroll < 0) {
positionsToMove *= -1;
}
if (mIsRTL) {
positionsToMove *= -1;
}
if (mLayoutDirectionHelper.isDirectionToBottom(scroll < 0)) {
// Scrolling toward the bottom of data.
return roundDownToBlockSize(llm.findFirstVisibleItemPosition()) + positionsToMove;
}
// Scrolling toward the top of the data.
return roundDownToBlockSize(llm.findLastVisibleItemPosition()) + positionsToMove;
}
boolean isDirectionToBottom(boolean velocityNegative) {
//noinspection SimplifiableConditionalExpression
return mIsRTL ? velocityNegative : !velocityNegative;
}
}
public interface SnapBlockCallback {
void onBlockSnap(int snapPosition);
void onBlockSnapped(int snapPosition);
}
private static final float MILLISECONDS_PER_INCH = 100f;
#SuppressWarnings("unused")
private static final String TAG = "SnapToBlock";
}
The SnapBlockCallback interface defined above can be used to report the adapter position of the view at the start of the block to be snapped. The view associated with that position may not be instantiated when the call is made if the view is off screen.
This library it is useful https://github.com/TakuSemba/MultiSnapRecyclerView
//Adding multisnap to the recyclerview
val multiSnapHelper = MultiSnapHelper(MultiSnapHelper.DEFAULT_GRAVITY, 1, 200F)
multiSnapHelper.attachToRecyclerView(recyclerView)
this code above is for your activity via code
<com.takusemba.multisnaprecyclerview.MultiSnapRecyclerView
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:msrv_gravity="start" or center, end
app:msrv_interval="2" items to scroll over
app:msrv_ms_per_inch="100" /> // speed of scrolling through.
and this is the same way but in xml it is your choice
all this information its from the documentation
I would do something like that
Block scrolling inside RecyclerView (e.g How to disable RecyclerView scrolling?)
Create Gesture Fling Detecor and attach it to RecyclerView
Inside Gesture Detector detect fling events events
On Fling event, detect side (left right)
Scroll RecyclerView to position (first Visible item + your const * (left?-1:1))
should work :)