int mDistanceY=0;
recyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
            @Override
            public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
            //滑动的距离
            mDistanceY += dy;
            //toolbar的高度
            int toolbarHeight = searchView.getBottom();
            //当滑动的距离 <= toolbar高度的时候，改变Toolbar背景色的透明度，达到渐变的效果
            if (mDistanceY <= toolbarHeight) {
                float scale = (float) mDistanceY / toolbarHeight;
                float alpha = scale * 255;
                searchView.setBackgroundColor(Color.argb((int) alpha, 255, 255, 255));
            } else {
                //将标题栏的颜色设置为完全不透明状态
                searchView.setBackgroundResource(R.color.white);
            }
        }
    });