title: make sliverAppBar hide title in expended mode
body: <p><a href="https://i.stack.imgur.com/xLcQq.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/xLcQq.png" alt="enter image description here"></a></p>
  
  <p>I'm testing code with SliverAppBar and make this widget , but there is an issue I want hide top bar that has "2 icons and title "categories Page " when SliverAppbar is expended but when I scrolling up it must show and flexibleSpace hide </p>
  
  <p>this is my code</p>
  
  <pre><code> return Scaffold(
    body: CustomScrollView(
      slivers: &lt;Widget&gt;[
        SliverAppBar(
          expandedHeight: 200,
          floating: false,
          pinned: true,
          snap: false,
          title: AppBar(),
          centerTitle: true,
  
          flexibleSpace: FlexibleSpaceBar(
            background: CenterAppBar(),
            // centerTitle: false,
            // titlePadding: EdgeInsets.all(0),
            // background: AppBar(),
          ),
        ),
        SliverList(
          delegate: SliverChildListDelegate([
            CategoryCard(),
            CategoryCard(),
            CategoryCard(),
            CategoryCard(),
            CategoryCard(),
            CategoryCard(),
            CategoryCard(),
            CategoryCard(),
            CategoryCard(),
            CategoryCard(),
                          CategoryCard(),
            CategoryCard(),
            CategoryCard(),
            CategoryCard(),
            CategoryCard(),
            CategoryCard(),
            CategoryCard(),
            CategoryCard(),
            CategoryCard(),
            CategoryCard(),
                          CategoryCard(),
            CategoryCard(),
            CategoryCard(),
            CategoryCard(),
            CategoryCard(),
            CategoryCard(),
            CategoryCard(),
            CategoryCard(),
            CategoryCard(),
            CategoryCard(),
          ]),
        )
      ],
    ),
  );
  </code></pre>