从源码可以看出，scrollBy内部调用了scrollTo,是在scrollTo的基础上进行的移动；顾名思义：scrollTo(x,y)那就是移向(x,y);scrollBy（x，y）就是在scrollTo的基础上在进行了移动！！

public void scrollBy(int x, int y) {
        scrollTo(mScrollX + x, mScrollY + y);
    }

public void scrollTo(int x, int y) {
        if (mScrollX != x || mScrollY != y) {
            int oldX = mScrollX;
            int oldY = mScrollY;
            mScrollX = x;
            mScrollY = y;
            invalidateParentCaches();
            onScrollChanged(mScrollX, mScrollY, oldX, oldY);
            if (!awakenScrollBars()) {
                postInvalidateOnAnimation();
            }
        }
    }