Flutter use SliverAppBar with Hero widget - flutter

Question

I'm having trouble using the Hero widget with SliverAppBar.
class MyHomePage extends StatelessWidget {
const MyHomePage({super.key});
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: const Text('Flutter Demo Home Page'),
),
body: Center(
child: Row(
children: [Colors.red, Colors.blue, Colors.yellow]
.map((e) => GestureDetector(
onTap: () {
Navigator.push(
context,
MaterialPageRoute(
builder: (_) => ScrollPage(color: e),
));
},
child: Hero(
tag: e,
child: Container(
width: 100,
height: 100,
color: e,
),
),
))
.toList(),
),
),
);
}
}
import 'package:flutter/material.dart';
class ScrollPage extends StatefulWidget {
const ScrollPage({super.key, required this.color});
final Color color;
#override
State<ScrollPage> createState() => _ScrollPageState();
}
class _ScrollPageState extends State<ScrollPage> {
// final GlobalKey key = GlobalKey<SliverState>();
#override
Widget build(BuildContext context) {
return Scaffold(
body: CustomScrollView(
slivers: [
Hero(
tag: widget.color,
child: SliverAppBar.large(
key: UniqueKey(),
expandedHeight: 200,
backgroundColor: widget.color,
title: const Text(
'This is a title blblaa',
),
),
),
SliverList(
delegate: SliverChildBuilderDelegate(
(context, index) => ListTile(
title: Text('Item $index'),
),
childCount: 100,
),
),
],
),
);
}
}
I'm getting error like:
════════ Exception caught by widgets library ═══════════════════════════════════
'package:flutter/src/widgets/framework.dart': Failed assertion: line 6405 pos 12: 'renderObject.child == child': is not true.
and
════════ Exception caught by widgets library ═══════════════════════════════════
'package:flutter/src/widgets/framework.dart': Failed assertion: line 6369 pos 12: 'child == _child': is not true.
framework.dart:6369
The relevant error-causing widget was
MaterialApp
and sometimes:
════════ Exception caught by widgets library ═══════════════════════════════════
Duplicate GlobalKey detected in widget tree.
════════════════════════════════════════════════════════════════════════════════
I did similar not using Appbar and I achieved it. Demo video here. But, I really want to use SliverAppbar in this case.
Full minimal reproducible project: https://github.com/iqfareez/flutter_hero_sliver
How do I make the SliverAppBar work with Hero?

Answer 1

The issue is here Hero is a general widget rather than a sliver-widget. That's the issue occurs while wrapping the SliverAppBar with Hero widget.
You can do
SliverToBoxAdapter(
child: Hero(
tag: widget.color,
child: // customAppBar but it might loss the scroll-effect,
Also, you can wrap the Scaffold with Hero widget, but it will show a little different animation.
You can create SliverPersistentHeaderDelegate.
Check the pr and commit difference.
import 'package:flutter/material.dart';
class ScrollPage extends StatefulWidget {
const ScrollPage({super.key, required this.color});
final Color color;
#override
State<ScrollPage> createState() => _ScrollPageState();
}
class _ScrollPageState extends State<ScrollPage> {
#override
Widget build(BuildContext context) {
return Scaffold(
body: CustomScrollView(
slivers: [
SliverPersistentHeader(
delegate: MySliverPersistentHeaderDelegate(widget.color)),
SliverList(
delegate: SliverChildBuilderDelegate(
(context, index) => ListTile(
title: Text('Item $index'),
),
childCount: 100,
),
),
],
),
);
}
}
class MySliverPersistentHeaderDelegate extends SliverPersistentHeaderDelegate {
final tag;
MySliverPersistentHeaderDelegate(this.tag);
#override
Widget build(
BuildContext context, double shrinkOffset, bool overlapsContent) {
return Hero(
tag: tag,
child: Material(
color: tag,
child: Stack(
children: [
Align(
child: const Text(
'This is a title blblaa',
),
),
Align(
alignment: Alignment.topLeft,
child: IconButton(
onPressed: () {
Navigator.of(context).pop();
},
icon: Icon(Icons.arrow_back)),
),
],
),
),
);
}
#override
double get maxExtent => 200;
#override
double get minExtent => kToolbarHeight;
#override
bool shouldRebuild(covariant SliverPersistentHeaderDelegate oldDelegate) =>
true;
}

Answer 2

You can try moving the Hero widget outside of the SliverAppBar, wrapping it around the entire CustomScrollView. Here's how you can modify your code to achieve that:
class MyHomePage extends StatelessWidget {
const MyHomePage({super.key});
#override
Widget build(BuildContext context) {
return Scaffold(
body: Hero(
tag: 'row',
child: Center(
child: Row(
children: [Colors.red, Colors.blue, Colors.yellow]
.map((e) => GestureDetector(
onTap: () {
Navigator.push(
context,
MaterialPageRoute(
builder: (_) => ScrollPage(color: e),
));
},
child: Container(
width: 100,
height: 100,
color: e,
),
))
.toList(),
),
),
),
);
}
}
class ScrollPage extends StatefulWidget {
const ScrollPage({super.key, required this.color});
final Color color;
#override
State<ScrollPage> createState() => _ScrollPageState();
}
class _ScrollPageState extends State<ScrollPage> {
// final GlobalKey key = GlobalKey<SliverState>();
#override
Widget build(BuildContext context) {
return Scaffold(
body: Hero(
tag: 'row',
child: CustomScrollView(
slivers: [
SliverAppBar(
key: UniqueKey(),
expandedHeight: 200,
backgroundColor: widget.color,
title: const Text(
'This is a title blblaa',
),
),
SliverList(
delegate: SliverChildBuilderDelegate(
(context, index) => ListTile(
title: Text('Item $index'),
),
childCount: 100,
),
),
],
),
),
);
}
}