Scroll View 涉及到的类

Scroll

OverScroller
  startScroll() 开始滚动
  computeScrollOffset() 方法不断计算滚动到的最新的位置，当滚动动画结束时，方法返回false。所以通常使用以下方式不断根据最新的位置绘制view来达到滚动的效果
  if (mScroller.computeScrollOffset()) {
            // This is called at drawing time by ViewGroup.  We use
            // this method to keep the fling animation going through
            // to completion.
            int oldX = getScrollX();
            int oldY = getScrollY();
            int x = mScroller.getCurrX();
            int y = mScroller.getCurrY();

            if (getChildCount() > 0) {
                View child = getChildAt(0);
                x = clamp(x, getWidth() - getPaddingRight() - getPaddingLeft(), child.getWidth());
                y = clamp(y, getHeight() - getPaddingBottom() - getPaddingTop(), child.getHeight());
                if (x != oldX || y != oldY) {
                    scrollTo(x, y);
                }
            }
            // Keep on drawing until the animation has finished.
            postInvalidate();
        }

VelocityTracker
  该类用来获取touch动作的瞬时速度，根据瞬时速度可以来实现fling效果
ViewConfiguration
  获取系统定义的一些touch常量
  
  
  //bounds check ScrollView中使用的方法
  /*
	 * Utility method to assist in doing bounds checking
	 */
    private int clamp(int n, int my, int child) {
        if (my >= child || n < 0) {
            /* my >= child is this case:
             *                    |--------------- me ---------------|
             *     |------ child ------|
             * or
             *     |--------------- me ---------------|
             *            |------ child ------|
             * or
             *     |--------------- me ---------------|
             *                                  |------ child ------|
             *
             * n < 0 is this case:
             *     |------ me ------|
             *                    |-------- child --------|
             *     |-- mScrollX --|
             */
            return 0;
        }
        if ((my+n) > child) {
            /* this case:
             *                    |------ me ------|
             *     |------ child ------|
             *     |-- mScrollX --|
             */
            return child-my;
        }
        return n;
    }