当用户到达终点时，如何实现RecyclerView项目的伸展效果？

import android.animation.Animator;
import android.animation.ValueAnimator;
import android.support.v7.widget.DefaultItemAnimator;
import android.support.v7.widget.RecyclerView;
import android.view.View;
import android.view.ViewGroup;

public class ExpandItemAnimator extends DefaultItemAnimator {

    private static final int ANIMATION_DURATION = 200;

    @Override
    public boolean animateChange(RecyclerView.ViewHolder oldHolder, RecyclerView.ViewHolder newHolder, int fromX, int fromY, int toX, int toY) {
        if (oldHolder != null && oldHolder instanceof YourViewHolder && newHolder != null && newHolder instanceof YourViewHolder) {
            final YourViewHolder viewHolder = (YourViewHolder) newHolder;
            final View itemView = viewHolder.itemView;

            if (viewHolder.isExpanded()) {
                // 折叠项目
                ValueAnimator animator = ValueAnimator.ofInt(itemView.getHeight(), viewHolder.getCollapsedHeight());
                animator.setDuration(ANIMATION_DURATION);
                animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
                    @Override
                    public void onAnimationUpdate(ValueAnimator valueAnimator) {
                        int height = (int) valueAnimator.getAnimatedValue();
                        ViewGroup.LayoutParams layoutParams = itemView.getLayoutParams();
                        layoutParams.height = height;
                        itemView.setLayoutParams(layoutParams);
                    }
                });
                animator.start();
            } else {
                // 展开项目
                ValueAnimator animator = ValueAnimator.ofInt(itemView.getHeight(), viewHolder.getExpandedHeight());
                animator.setDuration(ANIMATION_DURATION);
                animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
                    @Override
                    public void onAnimationUpdate(ValueAnimator valueAnimator) {
                        int height = (int) valueAnimator.getAnimatedValue();
                        ViewGroup.LayoutParams layoutParams = itemView.getLayoutParams();
                        layoutParams.height = height;
                        itemView.setLayoutParams(layoutParams);
                    }
                });
                animator.start();
            }

            return true;
        }

        return super.animateChange(oldHolder, newHolder, fromX, fromY, toX, toY);
    }
}