private boolean backBySpeed(float xvel, float yvel) {
        switch (dragEdge) {
            case TOP:
            case BOTTOM:
                if (Math.abs(yvel) > Math.abs(xvel) && Math.abs(yvel) > AUTO_FINISHED_SPEED_LIMIT) {
                    return dragEdge == DragEdge.TOP ? !canChildScrollUp() : !canChildScrollDown();
                }
                break;
            case LEFT:
            case RIGHT:
                if (Math.abs(xvel) > Math.abs(yvel) && Math.abs(xvel) > AUTO_FINISHED_SPEED_LIMIT) {
                    return dragEdge == DragEdge.LEFT ? !canChildScrollLeft() : !canChildScrollRight();
                }
                break;
        }
        return false;
    }
Find out the scrollable child view from a ViewGroup.

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