android.support.v4.view.ViewCompat#OVER_SCROLL_IF_CONTENT_SCROLLS源码实例Demo

@Override
public void computeScroll() {
    if (mScroller.computeScrollOffset()) {
        int oldX = getScrollX();
        int oldY = getScrollY();
        int x = mScroller.getCurrX();
        int y = mScroller.getCurrY();

        if (oldX != x || oldY != y) {
            final int range = getScrollRange();
            final int overscrollMode = ViewCompat.getOverScrollMode(this);
            final boolean canOverscroll = overscrollMode == ViewCompat.OVER_SCROLL_ALWAYS ||
                    (overscrollMode == ViewCompat.OVER_SCROLL_IF_CONTENT_SCROLLS && range > 0);

            overScrollByCompat(x - oldX, y - oldY, oldX, oldY, 0, range,
                    0, 0, false);

            if (canOverscroll) {
                ensureGlows();
                if (y <= 0 && oldY > 0) {
                    mEdgeGlowTop.onAbsorb((int) mScroller.getCurrVelocity());
                } else if (y >= range && oldY < range) {
                    mEdgeGlowBottom.onAbsorb((int) mScroller.getCurrVelocity());
                }
            }
        }
    }
}
 

boolean overScrollByCompat(int deltaX, int deltaY,
                               int scrollX, int scrollY,
                               int scrollRangeX, int scrollRangeY,
                               int maxOverScrollX, int maxOverScrollY,
                               boolean isTouchEvent) {
        final int overScrollMode = ViewCompat.getOverScrollMode(this);
        final boolean canScrollHorizontal =
                computeHorizontalScrollRange() > computeHorizontalScrollExtent();
        final boolean canScrollVertical =
                computeVerticalScrollRange() > computeVerticalScrollExtent();
        final boolean overScrollHorizontal = overScrollMode == ViewCompat.OVER_SCROLL_ALWAYS ||
                (overScrollMode == ViewCompat.OVER_SCROLL_IF_CONTENT_SCROLLS && canScrollHorizontal);
        final boolean overScrollVertical = overScrollMode == ViewCompat.OVER_SCROLL_ALWAYS ||
                (overScrollMode == ViewCompat.OVER_SCROLL_IF_CONTENT_SCROLLS && canScrollVertical);

        int newScrollX = scrollX + deltaX;
        if (!overScrollHorizontal) {
            maxOverScrollX = 0;
        }

        int newScrollY = scrollY + deltaY;
        if (!overScrollVertical) {
            maxOverScrollY = 0;
        }

        // Clamp values if at the limits and record
        final int left = -maxOverScrollX;
        final int right = maxOverScrollX + scrollRangeX;
        final int top = -maxOverScrollY;
        final int bottom = maxOverScrollY + scrollRangeY;

        boolean clampedX = false;
        if (newScrollX > right) {
            newScrollX = right;
            clampedX = true;
        } else if (newScrollX < left) {
            newScrollX = left;
            clampedX = true;
        }

        boolean clampedY = false;
        if (newScrollY > bottom) {
            newScrollY = bottom;
            clampedY = true;
        } else if (newScrollY < top) {
            newScrollY = top;
            clampedY = true;
        }

        if (clampedY) {
//            mScroller.springBack(newScrollX, newScrollY, 0, 0, 0, getScrollRange());
        }

        onOverScrolled(newScrollX, newScrollY, clampedX, clampedY);

        return clampedX || clampedY;
    }