@Override
        public void onViewDragStateChanged(int state) {
            if (state == draggingState) return;

            if ((draggingState == ViewDragHelper.STATE_DRAGGING || draggingState == ViewDragHelper.STATE_SETTLING) &&
                    state == ViewDragHelper.STATE_IDLE) {
                // the view stopped from moving.
                if (draggingOffset == getDragRange()) {
                    onFinishListener.onFinishState();
                }
            }

            draggingState = state;
        }
Find out the scrollable child view from a ViewGroup.

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