title: flutter - App bar scrolling with overlapping content in Flexible space
body: <p>i am trying to recreate App bar scrolling with overlapping content in Flexible space using flutter.</p>
  
  <p>the behavior is demonstrated here: </p>
  
  <p><a href="http://karthikraj.net/2016/12/24/scrolling-behavior-for-appbars-in-android/" rel="noreferrer">http://karthikraj.net/2016/12/24/scrolling-behavior-for-appbars-in-android/</a></p>
  
  <p><strong>I created collapsing AppBar using SliverAppBar already, using the code I pasted here, I am trying to create <a href="http://karthikraj.net/assets/scrolling/flexiSpaceContentOverlapping.gif" rel="noreferrer">THIS</a></strong> </p>
  
  <p>i cant use Stack for it because i cant find any onScroll callback, so far i created appbar with flexibleSpace, the app bar collapse on scroll:</p>
  
  <pre><code>Scaffold(
      body: NestedScrollView(
        headerSliverBuilder:
            (BuildContext context, bool innerBoxIsScrolled) =&gt; &lt;Widget&gt;[
                  SliverAppBar(
                    forceElevated: innerBoxIsScrolled,
                    pinned: true,
                    expandedHeight: 180.0,
                  ),
                ],
        body: ListView.builder(
          itemCount: 30,
          itemBuilder: (context, index) =&gt; Text(
                "Item $index",
                style: Theme.of(context).textTheme.display1,
              ),
        ),
      ),
    );
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/sDXdY.png" rel="noreferrer"><img src="https://i.stack.imgur.com/sDXdY.png" alt="What i created so far"></a></p>
  
  <p>edit: <a href="http://karthikraj.net/assets/scrolling/flexiSpaceContentOverlapping.gif" rel="noreferrer">Example of what i want to create</a></p>