scrollTo、scrollBy、smoothScrollTo和smoothScrollBy

下面是 scrollTo、scrollBy、smoothScrollTo 和 smoothScrollBy 效果图：

按钮添加的代码如下：

        scrollTo.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                scrollView.scrollTo(0, 100);
            }
        });

        scrollBy.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                scrollView.scrollBy(0, 100);
            }
        });

        smoothScrollTo.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                scrollView.smoothScrollTo(0, 1000);
            }
        });

        smoothScrollBy.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                scrollView.smoothScrollBy(0, 200);
            }
        });

scrollTo ：滑动到指定位置，如上面代码为：

scrollView.scrollTo(0, 100);

X 坐标不动，Y 轴滑动到100 坐标；即向下滑动 100 坐标；如果当前 Y 轴已经位于 100 坐标，则不滑动。

下面是源码描述 ：

    /**
     * {@inheritDoc}
     *
     * <p>This version also clamps the scrolling to the bounds of our child.
     */
    @Override
    public void scrollTo(int x, int y) {
        // we rely on the fact the View.scrollBy calls scrollTo.
        if (getChildCount() > 0) {
            View child = getChildAt(0);
            x = clamp(x, getWidth() - mPaddingRight - mPaddingLeft, child.getWidth());
            y = clamp(y, getHeight() - mPaddingBottom - mPaddingTop, child.getHeight());
            if (x != mScrollX || y != mScrollY) {
                super.scrollTo(x, y);
            }
        }
    }

scrollBy ：相对于之前坐标，滑动指定坐标，如上面的代码为：

scrollView.scrollBy(0, 100);

X 坐标不动，Y 轴滑动至（当前坐标 +100）坐标处；里面其实就是调用 scrollTo 方法。

下面是源码描述 ：

    /**
     * Move the scrolled position of your view. This will cause a call to
     * {@link #onScrollChanged(int, int, int, int)} and the view will be
     * invalidated.
     * @param x the amount of pixels to scroll by horizontally
     * @param y the amount of pixels to scroll by vertically
     */
    public void scrollBy(int x, int y) {
        scrollTo(mScrollX + x, mScrollY + y);
    }

smoothScrollTo ：平滑的滑动到指定坐标，类似于 scrollTo 方法，如上面代码为：

scrollView.smoothScrollTo(0, 1000);

X 轴坐标不动，Y 轴坐标滑动至 1000 处；

下面是源码描述：

    /**
     * Like {@link #scrollTo}, but scroll smoothly instead of immediately.
     *
     * @param x the position where to scroll on the X axis
     * @param y the position where to scroll on the Y axis
     */
    public final void smoothScrollTo(int x, int y) {
        smoothScrollBy(x - mScrollX, y - mScrollY);
    }

smoothScrollBy ：相对于之前坐标，平滑的滑动指定坐标，类似于 scrollBy 方法，如上面的代码为：

scrollView.smoothScrollBy(0, 200);

X 轴坐标不动，Y 轴滑动至（当前坐标 +200）坐标处。

下面是源码描述：

    /**
     * Like {@link View#scrollBy}, but scroll smoothly instead of immediately.
     *
     * @param dx the number of pixels to scroll by on the X axis
     * @param dy the number of pixels to scroll by on the Y axis
     */
    public final void smoothScrollBy(int dx, int dy) {
        if (getChildCount() == 0) {
            // Nothing to do.
            return;
        }
        long duration = AnimationUtils.currentAnimationTimeMillis() - mLastScroll;
        if (duration > ANIMATED_SCROLL_GAP) {
            final int height = getHeight() - mPaddingBottom - mPaddingTop;
            final int bottom = getChildAt(0).getHeight();
            final int maxY = Math.max(0, bottom - height);
            final int scrollY = mScrollY;
            dy = Math.max(0, Math.min(scrollY + dy, maxY)) - scrollY;

            mScroller.startScroll(mScrollX, scrollY, 0, dy);
            postInvalidateOnAnimation();
        } else {
            if (!mScroller.isFinished()) {
                mScroller.abortAnimation();
                if (mFlingStrictSpan != null) {
                    mFlingStrictSpan.finish();
                    mFlingStrictSpan = null;
                }
            }
            scrollBy(dx, dy);
        }
        mLastScroll = AnimationUtils.currentAnimationTimeMillis();
    }