Appbarlayou随rv滚动达成相应效果

   appbarlayout.addOnOffsetChangedListener(new AppBarLayout.OnOffsetChangedListener() {
            @Override
            public void onOffsetChanged(AppBarLayout appBarLayout, int verticalOffset) {
                if (Math.abs(verticalOffset * 1.0f) / appBarLayout.getTotalScrollRange() == 1) {
                    img.setImageResource(R.mipmap.home_messa_r);//滑动图片渐变
                } else {
                    img.setImageResource(R.mipmap.home_messa);
                }
                //滑动toolbar渐变
                toolbar.setBackgroundColor(changeAlpha(getResources().getColor(R.color.colorPrimaryDark), Math.abs(verticalOffset * 1.0f) / appBarLayout.getTotalScrollRange()));
            
            }
        });

 /**
     * 根据百分比改变颜色透明度
     */
    public int changeAlpha(int color, float fraction) {
        int red = Color.red(color);
        int green = Color.green(color);
        int blue = Color.blue(color);
        int alpha = (int) (Color.alpha(color) * fraction);
        return Color.argb(alpha, red, green, blue);
    }

一般 配合recycleview使用

 recycleview.addOnScrollListener(new RecyclerView.OnScrollListener() {
            int scrollY = 0;
            @Override
            public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
                super.onScrollStateChanged(recyclerView, newState);
                if (newState == RecyclerView.SCROLL_STATE_IDLE) {
                    //未滚动
                    if (!recyclerView.canScrollVertically(-1) && scrollY < -10) {
                        //do somthing
                        appbarlayout.setExpanded(true, true);//通知AppBarLayout伸展
                        scrollY = 0;
                    }
                }
                //判断慢速滚动：当滚动到顶部时靠手指拖动后的惯性让RecyclerView处于Fling状态时的速度大于5时，让AppBarLayout展开
                if (newState == RecyclerView.SCROLL_STATE_SETTLING) {
                    //正在滚动中，惯性滚动
                    if (!recyclerView.canScrollVertically(-1) && scrollY < -5) {
                        //do somthing
                        appbarlayout.setExpanded(true, true);
                        scrollY = 0;
                    }
                }
            }

            @Override
            public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                super.onScrolled(recyclerView, dx, dy);
                scrollY = dy;
            }
        });