Recylerview custom animator, issues on moving and adding elements

Question

I'm using a custom animator to animate two recycler in two different fragments with custom animations. Everything works, except a minor and a major issue. First thing first, here's the custom animator:

import android.animation.Animator
import android.animation.AnimatorListenerAdapter
import android.util.Log
import androidx.interpolator.view.animation.FastOutSlowInInterpolator
import androidx.recyclerview.widget.RecyclerView
import androidx.recyclerview.widget.SimpleItemAnimator


// A custom animator to animate the items in recycler view
class RecyclerAnimator : SimpleItemAnimator() {

    // Never called
    override fun animateRemove(viewHolder: RecyclerView.ViewHolder): Boolean {
        viewHolder.itemView.animate()
            .alpha(0F)
            .setInterpolator(FastOutSlowInInterpolator())
            .setStartDelay(200)
            .setDuration(300)
            .scaleY(0F)
            .setListener(object : AnimatorListenerAdapter() {
                override fun onAnimationEnd(animation: Animator) {
                    super.onAnimationEnd(animation)
                    dispatchRemoveFinished(viewHolder)
                }
            })
            .start()
        Log.d("recycler_animation", "animate remove")
        return false
    }

    // Called when the items appear in the list (launch, fragment change, it was created)
    override fun animateAdd(viewHolder: RecyclerView.ViewHolder): Boolean {
        val height: Int = viewHolder.itemView.measuredHeight / 3
        val view = viewHolder.itemView
        view.translationY = height.toFloat()
        view.alpha = 0F
        view.scaleY = 1F
        view.animate()
            .translationY(0F)
            .alpha(1F)
            .setInterpolator(FastOutSlowInInterpolator())
            .setDuration(400)
            .setStartDelay(viewHolder.bindingAdapterPosition * 50L)
            .setListener(object : AnimatorListenerAdapter() {
                override fun onAnimationEnd(animation: Animator) {
                    super.onAnimationEnd(animation)
                    dispatchAddFinished(viewHolder)
                }
            })
            .start()
        Log.d("recycler_animation", "animate add")
        return false
    }

    // Called when an item is being moved to another position in the adapter
    override fun animateMove(
        viewHolder: RecyclerView.ViewHolder,
        fromX: Int, fromY: Int,
        toX: Int, toY: Int
    ): Boolean {
        val item = viewHolder.itemView
        item.y = fromY.toFloat()
        val verticalMovement = if (toY > fromY)
            (toY - fromY).toFloat() - (item.measuredHeight)
        else (fromY - toY).toFloat() - (item.measuredHeight)
        item.animate()
            .translationY(verticalMovement)
            .setDuration(300)
            .setInterpolator(FastOutSlowInInterpolator())
            .setStartDelay(200)
            .setListener(object : AnimatorListenerAdapter() {
                override fun onAnimationEnd(animation: Animator) {
                    super.onAnimationEnd(animation)
                    dispatchMoveFinished(viewHolder)
                }
            })
            .start()
        Log.d("recycler_animation", "animate move")
        return false
    }

    // Called when an item changes its data
    override fun animateChange(
        oldHolder: RecyclerView.ViewHolder,
        newHolder: RecyclerView.ViewHolder,
        fromLeft: Int, fromTop: Int,
        toLeft: Int, toTop: Int
    ): Boolean {
        newHolder.itemView.alpha = 0F
        val oldAnimation = oldHolder.itemView.animate()
            .alpha(0F)
            .setInterpolator(FastOutSlowInInterpolator())
            .setDuration(300)
            .setListener(object : AnimatorListenerAdapter() {
                override fun onAnimationEnd(animation: Animator) {
                    super.onAnimationEnd(animation)
                    dispatchChangeFinished(oldHolder, true)
                }
            })
        val newAnimation = newHolder.itemView.animate()
            .alpha(1F)
            .setInterpolator(FastOutSlowInInterpolator())
            .setDuration(300)
            .setListener(object : AnimatorListenerAdapter() {
                override fun onAnimationEnd(animation: Animator) {
                    super.onAnimationEnd(animation)
                    dispatchChangeFinished(newHolder, false)
                }
            })
        oldAnimation.start()
        newAnimation.start()
        Log.d("recycler_animation", "animate change")
        return false
    }

    // Called when an item is deleted from the adapter
    override fun animateDisappearance(
        viewHolder: RecyclerView.ViewHolder,
        preLayoutInfo: ItemHolderInfo,
        postLayoutInfo: ItemHolderInfo?
    ): Boolean {
        viewHolder.itemView.animate()
            .alpha(0F)
            .setInterpolator(FastOutSlowInInterpolator())
            .setDuration(400)
            .setStartDelay(100)
            .scaleY(0F)
            .setListener(object : AnimatorListenerAdapter() {
                override fun onAnimationEnd(animation: Animator) {
                    super.onAnimationEnd(animation)
                    dispatchRemoveFinished(viewHolder)
                    viewHolder.itemView.alpha = 1F
                    viewHolder.itemView.scaleY = 1F
                }
            })
            .start()
        Log.d("recycler_animation", "animate disappearance")
        return false
    }

    override fun runPendingAnimations() {
        Log.d("recycler_animation", "pending animations")
    }

    override fun endAnimation(viewHolder: RecyclerView.ViewHolder) {
        Log.d("recycler_animation", "end animation")
        val item = viewHolder.itemView
        item.alpha = 1F
        item.translationY = 0F
        item.scaleY = 1F
    }

    override fun endAnimations() {
        Log.d("recycler_animation", "end animation no arg")
    }

    override fun isRunning(): Boolean {
        return false
    }


}

• First, major issue: i use two different viewholder layouts in one of the recycler views, and when the elements are moved (animateMove) the shorter elements are moved in the wrong position both when they move up or down. My guess is that the "measured height" is wrong, but i have no idea why. (This issue can be observed in the first part of the gif)
• Second, minor issue: since i use a delay to make the items appear gradually, when adding an item back in the list, if the item is in the upper part the animation has no delay, while if the item is in the lower part, the animation starts with a delay based on its position in the list. (This issue can be observed in the second part of the gif)

Any help is well appreciated, since i'm close to the desired effect

Answer 1

On the major issue, may be due to measuredHeight vs height.

From the View page. "A view actually possess two pairs of width and height values." "measured width and measured height. These dimensions define how big a view wants to be" "width and height. These dimensions define the actual size of the view on screen" Because you are calling measuredHeight, the actual height of the item in the final layout may not agree.

On the minor issue, have you tried returning "true" from the animate functions? The wording in the doc is really confusing, yet could be interpreted as "true if a call to runPendingAnimations is requested, false if start all animations together in a later call to runPendingAnimations"