ListView item scroll animation ("UIKit Dynamics" -like)

Question

I am attempting to animate the ListView items when a scroll takes place. More specifically, I am trying to emulate the scroll animations from the iMessage app on iOS 7. I found a similar example online:

To clarify, I'm trying to achieve the "fluid" movement effect on the items when the user scrolls, not the animation when a new item is added. I've attempted to modify the Views in my BaseAdapter and I've looked into the AbsListView source to see if I could somehow attach an AccelerateInterpolator somewhere that would adjust the draw coordinates sent to the children Views (if that is even how AbsListView is designed). I've been unable to make any progress so far.

Does anybody have any ideas of how to replicate this behaviour?

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For the record to help with googling: this is called "UIKit Dynamics" on ios.

How to replicate Messages bouncing bubbles in iOS 7

It is built-in to recent iOS releases. However it's still somewhat hard to use. (2014) This is the post on it everyone copies:widely copied article Surprisingly, UIKit Dynamics is only available on apple's "collection view", not on apple's "table view" so all the iOS debs are having to convert stuff from table view to "collection view"

The library everyone is using as a starting point is BPXLFlowLayout, since that person pretty much cracked copying the feel of the iphone text messages app. In fact, if you were porting it to Android I guess you could use the parameters in there to get the same feel. FYI I noticed in my android fone collection, HTC phones have this effect, on their UI. Hope it helps. Android rocks!

Answer 1

This implementation works quite good. There is some flickering though, probably because of altered indices when the adapter add new views to top or bottom..That could be possibly solved by watching for changes in the tree and shifting the indices on the fly..

public class ElasticListView extends GridView implements AbsListView.OnScrollListener,      View.OnTouchListener {

private static int SCROLLING_UP = 1;
private static int SCROLLING_DOWN = 2;

private int mScrollState;
private int mScrollDirection;
private int mTouchedIndex;

private View mTouchedView;

private int mScrollOffset;
private int mStartScrollOffset;

private boolean mAnimate;

private HashMap<View, ViewPropertyAnimator> animatedItems;


public ElasticListView(Context context) {
    super(context);
    init();
}

public ElasticListView(Context context, AttributeSet attrs) {
    super(context, attrs);
    init();
}

public ElasticListView(Context context, AttributeSet attrs, int defStyle) {
    super(context, attrs, defStyle);
    init();
}

private void init() {
    mScrollState = SCROLL_STATE_IDLE;
    mScrollDirection = 0;
    mStartScrollOffset = -1;
    mTouchedIndex = Integer.MAX_VALUE;
    mAnimate = true;
    animatedItems = new HashMap<>();
    this.setOnTouchListener(this);
    this.setOnScrollListener(this);

}


@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
    if (mScrollState != scrollState) {
        mScrollState = scrollState;
        mAnimate = true;

    }
    if (scrollState == SCROLL_STATE_IDLE) {
        mStartScrollOffset = Integer.MAX_VALUE;
        mAnimate = true;
        startAnimations();
    }

}

@Override
public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {

    if (mScrollState == SCROLL_STATE_TOUCH_SCROLL) {

        if (mStartScrollOffset == Integer.MAX_VALUE) {
            mTouchedView = getChildAt(mTouchedIndex - getPositionForView(getChildAt(0)));
            if (mTouchedView == null) return;

            mStartScrollOffset = mTouchedView.getTop();
        } else if (mTouchedView == null) return;

        mScrollOffset = mTouchedView.getTop() - mStartScrollOffset;
        int tmpScrollDirection;
        if (mScrollOffset > 0) {

            tmpScrollDirection = SCROLLING_UP;

        } else {
            tmpScrollDirection = SCROLLING_DOWN;
        }

        if (mScrollDirection != tmpScrollDirection) {
            startAnimations();
            mScrollDirection = tmpScrollDirection;
        }


        if (Math.abs(mScrollOffset) > 200) {
            mAnimate = false;
            startAnimations();
        }
        Log.d("test", "direction:" + (mScrollDirection == SCROLLING_UP ? "up" : "down") + ", scrollOffset:" + mScrollOffset + ", toucheId:" + mTouchedIndex + ", fvisible:" + firstVisibleItem + ", " +
            "visibleItemCount:" + visibleItemCount + ", " +
            "totalCount:" + totalItemCount);
        int indexOfLastAnimatedItem = mScrollDirection == SCROLLING_DOWN ?
            getPositionForView(getChildAt(0)) + getChildCount() :
            getPositionForView(getChildAt(0));

        //check for bounds
        if (indexOfLastAnimatedItem >= getChildCount()) {
            indexOfLastAnimatedItem = getChildCount() - 1;
        } else if (indexOfLastAnimatedItem < 0) {
            indexOfLastAnimatedItem = 0;
        }

        if (mScrollDirection == SCROLLING_DOWN) {
            setAnimationForScrollingDown(mTouchedIndex - getPositionForView(getChildAt(0)), indexOfLastAnimatedItem, firstVisibleItem);
        } else {
            setAnimationForScrollingUp(mTouchedIndex - getPositionForView(getChildAt(0)), indexOfLastAnimatedItem, firstVisibleItem);
        }
        if (Math.abs(mScrollOffset) > 200) {
            mAnimate = false;
            startAnimations();
            mTouchedView = null;
            mScrollDirection = 0;
            mStartScrollOffset = -1;
            mTouchedIndex = Integer.MAX_VALUE;
            mAnimate = true;
        }
    }
}

private void startAnimations() {
    for (ViewPropertyAnimator animator : animatedItems.values()) {
        animator.start();
    }
    animatedItems.clear();
}

private void setAnimationForScrollingDown(int indexOfTouchedChild, int indexOflastAnimatedChild, int firstVisibleIndex) {
    for (int i = indexOfTouchedChild + 1; i <= indexOflastAnimatedChild; i++) {
        View v = getChildAt(i);
        v.setTranslationY((-1f * mScrollOffset));
        if (!animatedItems.containsKey(v)) {
            animatedItems.put(v, v.animate().translationY(0).setDuration(300).setStartDelay(50 * i));
        }

    }
}

private void setAnimationForScrollingUp(int indexOfTouchedChild, int indexOflastAnimatedChild, int firstVisibleIndex) {
    for (int i = indexOfTouchedChild - 1; i > 0; i--) {
        View v = getChildAt(i);

        v.setTranslationY((-1 * mScrollOffset));
        if (!animatedItems.containsKey(v)) {
            animatedItems.put(v, v.animate().translationY(0).setDuration(300).setStartDelay(50 * (indexOfTouchedChild - i)));
        }

    }
}


@Override
public boolean onTouch(View v, MotionEvent event) {
    switch (event.getActionMasked()) {
        case MotionEvent.ACTION_DOWN:
            Rect rect = new Rect();
            int childCount = getChildCount();
            int[] listViewCoords = new int[2];
            getLocationOnScreen(listViewCoords);
            int x = (int)event.getRawX() - listViewCoords[0];
            int y = (int)event.getRawY() - listViewCoords[1];
            View child;
            for (int i = 0; i < childCount; i++) {
                child = getChildAt(i);
                child.getHitRect(rect);
                if (rect.contains(x, y)) {
                    mTouchedIndex = getPositionForView(child); 
                    break;
                }
            }
            return false;

    }
    return false;

}

}