How to change SliverAppBar height dynamically - flutter

Question

I show image from network, which shrink on scrolling. I want to show whole image without paddings or crops. But if I comment line with expandedHeight - there is no image - only appbar with its height. Is there any widget, which can change its size according to size of uploaded image?
CustomScrollView(
controller: controller,
key: listKey,
slivers: <Widget>[
SliverAppBar(
// expandedHeight: 200.0,
flexibleSpace: FlexibleSpaceBar(
background: getHeroWidget(
_conference.dbId,
FadeInImage.assetNetwork(
placeholder: conf_img_placeholder,
image: _conference.info.image,
fit: BoxFit.cover,
)),
title: Text(conference_title),
centerTitle: true,
),
pinned: true,
),

Answer 1

Finally I created custom SliverAppBar. Another issue appears - width of status bar which have to be taken into consideration on calculation.
import 'dart:ui' as ui;
class _HeaderBar extends StatefulWidget {
#override
State<StatefulWidget> createState() => _HeaderState();
}
class _HeaderState extends State<_HeaderBar> {
#override
Widget build(BuildContext context) {
Image image = Image.network(...);
Completer<ui.Image> completer = new Completer<ui.Image>();
image.image.resolve(ImageConfiguration()).addListener((ImageInfo info, bool _) {
completer.complete(info.image);
});
final double statusBarHeight = MediaQuery.of(context).padding.top;
return FutureBuilder(
future: completer.future,
builder: (context, AsyncSnapshot<ui.Image> snapshot) {
return SliverAppBar(
expandedHeight: snapshot.hasData
? MediaQuery.of(context).size.width / snapshot.data.width.toDouble() * snapshot.data.height.toDouble() -
statusBarHeight
: 0.0,
...

Answer 2

I was looking for this problem, I find a solution with NestedScrollView and a plugin SliverStickyHeader
Here is how I did this,
Scaffold(
body: SafeArea(
child: NestedScrollView(
headerSliverBuilder: (BuildContext context, bool innerBoxIsScrolled) {
return <Widget>[
SliverStickyHeader(
sticky: false,
header: Container(
color: Theme.of(context).primaryColor,
child: Column(
children: [
Text(
'Header',
style: Theme.of(context).textTheme.headline6,
),
Text(
'Header',
style: Theme.of(context).textTheme.headline5,
),
Text(
'Header',
style: Theme.of(context).textTheme.headline4,
),
Text(
'Header',
style: Theme.of(context).textTheme.headline3,
),
],
),
),
)
];
},
body: Column(
children: [
AppBar(
title: Text('My List items'),
),
Expanded(
child: ListView.builder(itemBuilder: (context, i) {
return ListTile(
leading: CircleAvatar(child: Text('$i')),
title: Text('Appbar with dynamic height'),
);
}),
),
],
),
),
),
);
and it is fulfilling my requirement, Plugin also support fully Sliver functionality, but I use it with as header only. I hope it will be helpful.