title: Flutter SliverAppBar content resize on scroll down
body: <p>I've got some issues with the sliver app bar and it's content. I want to resize the image in the flexibleSpace when I scroll down the content of SliverList (in a code down below), to fit image the top element in a list.</p>
  <p>Right now, I have this (holding drag position here):<a href="https://i.stack.imgur.com/5itzJ.jpg" rel="nofollow noreferrer">click</a></p>
  <p>And I want to come up with something like that (and bouncing back to initial expandedHeight on drag ended):<a href="https://i.stack.imgur.com/Nikns.jpg" rel="nofollow noreferrer">click</a></p>
  <p>Tbh, I don't have any ideas on how to achieve this behavior using the sliver app bar, any help would be appreciated!</p>
  <p>Here is my code</p>
  <pre><code>  @override
    Widget build(BuildContext context) {
      return Scaffold(
        body: CustomScrollView(slivers: [
          SliverAppBar(
            elevation: 0,
            expandedHeight: 360,
            floating: false,
            pinned: false,
            snap: false,
            flexibleSpace: FlexibleSpaceBar(
                centerTitle: false,
                title: Text('Running running'),
                background: Image.asset(
                  'assets/images/excercise_3.jpg',
                  fit: BoxFit.cover,
                )),
          ),
          SliverList(
              delegate: SliverChildListDelegate([
            _TopInfo(),
            _MainContent(),
          ]))
        ]),
      );
    }
  </code></pre>