private void smoothScrollToX(int finalLeft) {
        if (viewDragHelper.settleCapturedViewAt(finalLeft, 0)) {
            ViewCompat.postInvalidateOnAnimation(SwipeBackLayout.this);
        }
    }
Find out the scrollable child view from a ViewGroup.

@param viewGroup
library/src/main/java/com/liuguangqiang/swipeback/SwipeBackLayout.java