NestedScrollView and Horizontal RecyclerView Smooth Scrolling

Question

I have a single vertical nestedscrollview that contains a bunch of recyclerview with a horizontal layoutmanager setup. The idea is pretty similar to how the new google play

Answer 1

So the smooth scrolling issue is fixed now. It was caused by a bug in the NestedScrollView in the Design Support Library (currently 23.1.1).

You can read about the issue and the simple fix here: https://code.google.com/p/android/issues/detail?id=194398

In short, after you performed a fling, the nestedscrollview didn't register a complete on the scroller component and so it needed an additional 'ACTION_DOWN' event to release the parent nestedscrollview from intercepting(eating up) the subsequent events. So what happened was if you tried scrolling your child list(or viewpager), after a fling, the first touch releases the parent NSV bind and the subsequent touches would work. That was making the UX really bad.

Essentially need to add this line on the ACTION_DOWN event of the NSV:

computeScroll();

Here is what I'm using:

public class MyNestedScrollView extends NestedScrollView {
private int slop;
private float mInitialMotionX;
private float mInitialMotionY;

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

private void init(Context context) {
    ViewConfiguration config = ViewConfiguration.get(context);
    slop = config.getScaledEdgeSlop();
}

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

public MyNestedScrollView(Context context, AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
    init(context);
}


private float xDistance, yDistance, lastX, lastY;

@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
    final float x = ev.getX();
    final float y = ev.getY();
    switch (ev.getAction()) {
        case MotionEvent.ACTION_DOWN:
            xDistance = yDistance = 0f;
            lastX = ev.getX();
            lastY = ev.getY();

            // This is very important line that fixes 
           computeScroll();


            break;
        case MotionEvent.ACTION_MOVE:
            final float curX = ev.getX();
            final float curY = ev.getY();
            xDistance += Math.abs(curX - lastX);
            yDistance += Math.abs(curY - lastY);
            lastX = curX;
            lastY = curY;

            if (xDistance > yDistance) {
                return false;
            }
    }


    return super.onInterceptTouchEvent(ev);
}

}

Use this class in place of your nestedscrollview in the xml file, and the child lists should intercept and handle the touch events properly.

Phew, there are actually quite a few bugs like these that makes me want to ditch the design support library altogether and revisit it when its more mature.