Android ListView，RecyclerView滑動標題漸變

ListView:

            //ListVie滑動觸動的接口
           public AbsListView.OnScrollListener onScrollListener = new AbsListView.OnScrollListener() {
                @Override
                public void onScrollStateChanged(AbsListView view, int scrollState) {

                }

                @Override
                public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int
                        totalItemCount) {
                    if (getScrollY() <= 0) {
                        countyRelative.getBackground().setAlpha(0);
                    } else if (getScrollY() > 0 && getScrollY() <= 300) {
                        float scale = (float) getScrollY() / 300;
                        float alpha = (255 * scale);
                        countyRelative.getBackground().setAlpha((int) alpha);
                    } else {
                        countyRelative.getBackground().setAlpha(255);
                    }
                }
            };


            public int getScrollY() {
                View c = storeListView.getChildAt(0);
                if (c == null) {
                    return 0;
                }
                int firstVisiblePosition = storeListView.getFirstVisiblePosition();
                int top = c.getTop();
                return -top + firstVisiblePosition * c.getHeight();
            }

RecyclerView：

                //標題欄漸變
                //滑動的距離
                disY += dy;
                //toolbar的高度
                int toolbarHeight = 300;
                if (disY <= toolbarHeight) {
                    float scale = (float) disY / 300;
                    float alpha = (255 * scale);
                    relativeLayout.getBackground().setAlpha((int) alpha);
                } else {
                    relativeLayout.getBackground().setAlpha(255);
                }

disY 默認爲0；