title: How to customize the SliverAppBar widget in flutter?
body: <p><a href="https://i.stack.imgur.com/Sw0PH.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Sw0PH.png" alt="enter image description here"></a></p>
  
  <p>I would like to add some more information in the green area, but when user scrolls up, I keep the <code>_ SliverAppBar</code> on the top..., like this:</p>
  
  <p><a href="https://i.stack.imgur.com/lh2QQ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/lh2QQ.png" alt="enter image description here"></a></p>
  
  <p>Here is my current source code:</p>
  
  <pre><code>body: new CustomScrollView(slivers: &lt;Widget&gt;[
            const SliverAppBar(
              pinned: true,
              expandedHeight: 300.0, // TODO: check out later
              flexibleSpace: const FlexibleSpaceBar(
                title: const Text('_SliverAppBar')
              ),
            ),
            new SliverList(delegate: new SliverChildListDelegate(_galleryListItems()))
          ]),
  </code></pre>