根据NestedScrollView的滑动来渐变显示Title。

  nestedScrollView.setOnScrollChangeListener((NestedScrollView.OnScrollChangeListener) (nestedScrollView, i, i1, i2, i3) -> {
            int height = dp2Px(45, getContext());

            if (i1 <= 0) {
                tv_title.setText("教师资格证");
                tv_title.setAlpha(0);
            } else if (i1 > 0 && i1 < height) {
                tv_title.setText("教师资格证");
                //获取渐变率
                float scale = (float) i1 / height;
                //获取渐变数值
                float alpha = (1.0f * scale);
                tv_title.setAlpha(alpha);
            } else {
                tv_title.setAlpha(1f);
            }

        });