Flutter : Image Lost in SliverAppBar - flutter

Question

I'm Working with SliverAppBar.
Previous I have 2 Page Let's Say (Search,and Detail) ,
In Detail Page,I have problem When i Scroll Down and make Image not visible after that I'm press button Back , My Image lost in Search Page. But if i Scroll down and then little Scroll Up to make Image visible after that i press Back button , My image not lost and still stay there.
It's may be confusing, but you can see the GIF for more detail.
Can you help Me with this ?
Thank's
It's Detail.dart :
import 'package:flutter/material.dart';
import 'package:flutter_news/model/Berita_model.dart';
import 'package:flutter_news/widget/Widget_builder.dart';
class WartawanDetail extends StatefulWidget {
final int idWartawan;
final String gambarWartawan;
final String namaWartawan;
WartawanDetail({this.idWartawan, this.gambarWartawan, this.namaWartawan});
#override
_WartawanDetailState createState() => _WartawanDetailState();
}
class _WartawanDetailState extends State<WartawanDetail> {
#override
Widget build(BuildContext context) {
return Scaffold(
body: CustomScrollView(
slivers: <Widget>[
SliverAppBar(
floating: true,
pinned: false,
leading: IconButton(
icon: Icon(Icons.arrow_left),
onPressed: () => Navigator.pop(context),
),
expandedHeight: 300.0,
centerTitle: true,
flexibleSpace: FlexibleSpaceBar(
background: Hero(
tag: widget.idWartawan,
child: Container(
decoration: BoxDecoration(
image: DecorationImage(
image: AssetImage(widget.gambarWartawan),
fit: BoxFit.cover),
),
child: Stack(
children: <Widget>[
Positioned(
bottom: 10,
left: 10,
child: Material(
color: Colors.transparent,
child: Chip(
backgroundColor: Colors.blue,
labelStyle: TextStyle(color: Colors.white),
label: Text(widget.namaWartawan),
),
),
),
Positioned(
bottom: 10,
right: 10,
child: Material(
color: Colors.transparent,
child: Chip(
backgroundColor: Colors.blue,
labelStyle: TextStyle(color: Colors.white),
label: Text("2 Berita"),
),
),
),
],
),
),
),
),
actions: <Widget>[
IconButton(
icon: Icon(Icons.more_horiz),
onPressed: () => "",
),
],
),
SliverFixedExtentList(
itemExtent: MediaQuery.of(context).size.height,
delegate: SliverChildListDelegate(
[
Container(
padding: EdgeInsets.all(8),
child: ListView.builder(
shrinkWrap: true,
physics: NeverScrollableScrollPhysics(),
itemCount: beritas.length,
itemBuilder: newsBuilderHome),
),
],
),
)
],
),
);
}
}
It's My Search.dart
Widget wartawanBuilderSearch(BuildContext context, int index) {
ThemeData localTheme = Theme.of(context);
return Container(
margin: EdgeInsets.all(8),
child: Column(
crossAxisAlignment: CrossAxisAlignment.center,
children: <Widget>[
Expanded(
child: Container(
child: Hero(
tag: wartawans[index].idWartawan,
child: Material(
color: Colors.transparent,
child: InkWell(
onTap: () => Navigator.push(
context,
PageTransition(
type: PageTransitionType.downToUp,
child: WartawanDetail(
idWartawan:wartawans[index].idWartawan,
gambarWartawan: wartawans[index].gambarWartawan,
namaWartawan: wartawans[index].namaWartawan,
),
),
),
child: CircleAvatar(
backgroundColor: Colors.red,
radius: 50,
backgroundImage:
AssetImage(wartawans[index].gambarWartawan),
),
),
),
),
),
),
Container(
child: Align(
alignment: Alignment.bottomLeft,
child: Text(
wartawans[index].namaWartawan,
style: localTheme.textTheme.caption
.copyWith(fontSize: 14, fontWeight: FontWeight.bold),
overflow: TextOverflow.ellipsis,
),
),
)
],
),
);
}