title: Flutter - SliverAppBar - How to show the AppBar as soon as user starts scrolling back up
body: <p>I have a SliverAppBar in a NestedScrollView. This hides the AppBar when the user scrolls down the screen, and it appears when the user scrolls back to the top.</p>
  <pre><code>NestedScrollView(
    controller: _scrollViewController,
    headerSliverBuilder: (BuildContext context, bool innerBoxIsScrolled) {
      return &lt;Widget&gt;[
        SliverAppBar(
          title: Text('Title'),
        ),
      ];
    },
      .......
  )
  </code></pre>
  <p>Currently, the AppBar remains hidden when user is scrolling up, and appears only when the scroll reaches almost to the top. I want the AppBar to appear as soon as the user starts scrolling upward. How to achieve this? I have tried the floating and pinned attributes.</p>